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docs/source/getting_started/example_synth.rst
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@ -2,13 +2,12 @@ Synthesis starter
-----------------
This page will be a guided walkthrough of the prepackaged iCE40 FPGA synthesis
script - `synth_ice40`. We will take a simple design through each
step, looking at the commands being called and what they do to the design. While
`synth_ice40` is specific to the iCE40 platform, most of the operations
we will be discussing are common across the majority of FPGA synthesis scripts.
Thus, this document will provide a good foundational understanding of how
synthesis in Yosys is performed, regardless of the actual architecture being
used.
script - `synth_ice40`. We will take a simple design through each step, looking
at the commands being called and what they do to the design. While `synth_ice40`
is specific to the iCE40 platform, most of the operations we will be discussing
are common across the majority of FPGA synthesis scripts. Thus, this document
will provide a good foundational understanding of how synthesis in Yosys is
performed, regardless of the actual architecture being used.
.. seealso:: Advanced usage docs for
:doc:`/using_yosys/synthesis/synth`
@ -105,10 +104,10 @@ Since we're just getting started, let's instead begin with :yoscrypt:`hierarchy
.. note::
`hierarchy` should always be the first command after the design has
been read. By specifying the top module, `hierarchy` will also set
the ``(* top *)`` attribute on it. This is used by other commands that need
to know which module is the top.
`hierarchy` should always be the first command after the design has been
read. By specifying the top module, `hierarchy` will also set the ``(* top
*)`` attribute on it. This is used by other commands that need to know which
module is the top.
.. use doscon for a console-like display that supports the `yosys> [command]` format.
@ -129,20 +128,20 @@ Our ``addr_gen`` circuit now looks like this:
Simple operations like ``addr + 1`` and ``addr == MAX_DATA-1`` can be extracted
from our ``always @`` block in :ref:`addr_gen-v`. This gives us the highlighted
`$add` and `$eq` cells we see. But control logic (like the ``if .. else``)
and memory elements (like the ``addr <= 0``) are not so straightforward. These
get put into "processes", shown in the schematic as ``PROC``. Note how the
second line refers to the line numbers of the start/end of the corresponding
``always @`` block. In the case of an ``initial`` block, we instead see the
``PROC`` referring to line 0.
`$add` and `$eq` cells we see. But control logic (like the ``if .. else``) and
memory elements (like the ``addr <= 0``) are not so straightforward. These get
put into "processes", shown in the schematic as ``PROC``. Note how the second
line refers to the line numbers of the start/end of the corresponding ``always
@`` block. In the case of an ``initial`` block, we instead see the ``PROC``
referring to line 0.
To handle these, let us now introduce the next command: :doc:`/cmd/proc`.
`proc` is a macro command like `synth_ice40`. Rather than
modifying the design directly, it instead calls a series of other commands. In
the case of `proc`, these sub-commands work to convert the behavioral
logic of processes into multiplexers and registers. Let's see what happens when
we run it. For now, we will call :yoscrypt:`proc -noopt` to prevent some
automatic optimizations which would normally happen.
To handle these, let us now introduce the next command: :doc:`/cmd/proc`. `proc`
is a macro command like `synth_ice40`. Rather than modifying the design
directly, it instead calls a series of other commands. In the case of `proc`,
these sub-commands work to convert the behavioral logic of processes into
multiplexers and registers. Let's see what happens when we run it. For now, we
will call :yoscrypt:`proc -noopt` to prevent some automatic optimizations which
would normally happen.
.. figure:: /_images/code_examples/fifo/addr_gen_proc.*
:class: width-helper invert-helper
@ -151,19 +150,18 @@ automatic optimizations which would normally happen.
``addr_gen`` module after :yoscrypt:`proc -noopt`
There are now a few new cells from our ``always @``, which have been
highlighted. The ``if`` statements are now modeled with `$mux` cells, while
the register uses an `$adff` cell. If we look at the terminal output we can
also see all of the different ``proc_*`` commands being called. We will look at
each of these in more detail in :doc:`/using_yosys/synthesis/proc`.
highlighted. The ``if`` statements are now modeled with `$mux` cells, while the
register uses an `$adff` cell. If we look at the terminal output we can also
see all of the different ``proc_*`` commands being called. We will look at each
of these in more detail in :doc:`/using_yosys/synthesis/proc`.
Notice how in the top left of :ref:`addr_gen_proc` we have a floating wire,
generated from the initial assignment of 0 to the ``addr`` wire. However, this
initial assignment is not synthesizable, so this will need to be cleaned up
before we can generate the physical hardware. We can do this now by calling
`clean`. We're also going to call `opt_expr` now, which would
normally be called at the end of `proc`. We can call both commands at
the same time by separating them with a colon and space: :yoscrypt:`opt_expr;
clean`.
`clean`. We're also going to call `opt_expr` now, which would normally be
called at the end of `proc`. We can call both commands at the same time by
separating them with a colon and space: :yoscrypt:`opt_expr; clean`.
.. figure:: /_images/code_examples/fifo/addr_gen_clean.*
:class: width-helper invert-helper
@ -171,24 +169,24 @@ clean`.
``addr_gen`` module after :yoscrypt:`opt_expr; clean`
You may also notice that the highlighted `$eq` cell input of ``255`` has
changed to ``8'11111111``. Constant values are presented in the format
You may also notice that the highlighted `$eq` cell input of ``255`` has changed
to ``8'11111111``. Constant values are presented in the format
``<bit_width>'<bits>``, with 32-bit values instead using the decimal number.
This indicates that the constant input has been reduced from 32-bit wide to
8-bit wide. This is a side-effect of running `opt_expr`, which
performs constant folding and simple expression rewriting. For more on why
this happens, refer to :doc:`/using_yosys/synthesis/opt` and the :ref:`section
on opt_expr <adv_opt_expr>`.
8-bit wide. This is a side-effect of running `opt_expr`, which performs
constant folding and simple expression rewriting. For more on why this
happens, refer to :doc:`/using_yosys/synthesis/opt` and the :ref:`section on
opt_expr <adv_opt_expr>`.
.. note::
:doc:`/cmd/clean` can also be called with two semicolons after any command,
for example we could have called :yoscrypt:`opt_expr;;` instead of
:yoscrypt:`opt_expr; clean`. You may notice some scripts will end each line
with ``;;``. It is beneficial to run `clean` before inspecting
intermediate products to remove disconnected parts of the circuit which have
been left over, and in some cases can reduce the processing required in
subsequent commands.
with ``;;``. It is beneficial to run `clean` before inspecting intermediate
products to remove disconnected parts of the circuit which have been left
over, and in some cases can reduce the processing required in subsequent
commands.
.. todo:: consider a brief glossary for terms like adff
@ -202,8 +200,8 @@ The full example
Let's now go back and check on our full design by using :yoscrypt:`hierarchy
-check -top fifo`. By passing the ``-check`` option there we are also telling
the `hierarchy` command that if the design includes any non-blackbox
modules without an implementation it should return an error.
the `hierarchy` command that if the design includes any non-blackbox modules
without an implementation it should return an error.
Note that if we tried to run this command now then we would get an error. This
is because we already removed all of the modules other than ``addr_gen``. We
@ -221,13 +219,12 @@ could restart our shell session, but instead let's use two new commands:
Notice how this time we didn't see any of those ``$abstract`` modules? That's
because when we ran ``yosys fifo.v``, the first command Yosys called was
:yoscrypt:`read_verilog -defer fifo.v`. The ``-defer`` option there tells
`read_verilog` only read the abstract syntax tree and defer actual
compilation to a later `hierarchy` command. This is useful in cases
where the default parameters of modules yield invalid code which is not
synthesizable. This is why Yosys defers compilation automatically and is one of
the reasons why hierarchy should always be the first command after loading the
design. If we know that our design won't run into this issue, we can skip the
``-defer``.
`read_verilog` only read the abstract syntax tree and defer actual compilation
to a later `hierarchy` command. This is useful in cases where the default
parameters of modules yield invalid code which is not synthesizable. This is why
Yosys defers compilation automatically and is one of the reasons why hierarchy
should always be the first command after loading the design. If we know that
our design won't run into this issue, we can skip the ``-defer``.
.. todo:: `hierarchy` failure modes
@ -243,13 +240,13 @@ design. If we know that our design won't run into this issue, we can skip the
interactive terminal. :kbd:`ctrl+c` (i.e. SIGINT) will also end the terminal
session but will return an error code rather than exiting gracefully.
We can also run `proc` now to finish off the full :ref:`synth_begin`.
Because the design schematic is quite large, we will be showing just the data
path for the ``rdata`` output. If you would like to see the entire design for
yourself, you can do so with :doc:`/cmd/show`. Note that the `show`
command only works with a single module, so you may need to call it with
:yoscrypt:`show fifo`. :ref:`show_intro` section in
:doc:`/getting_started/scripting_intro` has more on how to use `show`.
We can also run `proc` now to finish off the full :ref:`synth_begin`. Because
the design schematic is quite large, we will be showing just the data path for
the ``rdata`` output. If you would like to see the entire design for yourself,
you can do so with :doc:`/cmd/show`. Note that the `show` command only works
with a single module, so you may need to call it with :yoscrypt:`show fifo`.
:ref:`show_intro` section in :doc:`/getting_started/scripting_intro` has more on
how to use `show`.
.. figure:: /_images/code_examples/fifo/rdata_proc.*
:class: width-helper invert-helper
@ -321,11 +318,10 @@ merging happened during the call to `clean` which we can see in the
output.
Depending on the target architecture, this stage of synthesis might also see
commands such as `tribuf` with the ``-logic`` option and
`deminout`. These remove tristate and inout constructs respectively,
replacing them with logic suitable for mapping to an FPGA. Since we do not have
any such constructs in our example running these commands does not change our
design.
commands such as `tribuf` with the ``-logic`` option and `deminout`. These
remove tristate and inout constructs respectively, replacing them with logic
suitable for mapping to an FPGA. Since we do not have any such constructs in
our example running these commands does not change our design.
The coarse-grain representation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@ -342,9 +338,9 @@ optimizations and other transformations done previously.
.. note::
While the iCE40 flow had a :ref:`synth_flatten` and put `proc` in
the :ref:`synth_begin`, some synthesis scripts will instead include these in
this section.
While the iCE40 flow had a :ref:`synth_flatten` and put `proc` in the
:ref:`synth_begin`, some synthesis scripts will instead include these in this
section.
Part 1
^^^^^^
@ -359,24 +355,23 @@ In the iCE40 flow, we start with the following commands:
:caption: ``coarse`` section (part 1)
:name: synth_coarse1
We've already come across `opt_expr`, and `opt_clean` is the
same as `clean` but with more verbose output. The `check`
pass identifies a few obvious problems which will cause errors later. Calling
it here lets us fail faster rather than wasting time on something we know is
impossible.
We've already come across `opt_expr`, and `opt_clean` is the same as `clean` but
with more verbose output. The `check` pass identifies a few obvious problems
which will cause errors later. Calling it here lets us fail faster rather than
wasting time on something we know is impossible.
Next up is :yoscrypt:`opt -nodffe -nosdff` performing a set of simple
optimizations on the design. This command also ensures that only a specific
subset of FF types are included, in preparation for the next command:
:doc:`/cmd/fsm`. Both `opt` and `fsm` are macro commands
which are explored in more detail in :doc:`/using_yosys/synthesis/opt` and
:doc:`/cmd/fsm`. Both `opt` and `fsm` are macro commands which are explored in
more detail in :doc:`/using_yosys/synthesis/opt` and
:doc:`/using_yosys/synthesis/fsm` respectively.
Up until now, the data path for ``rdata`` has remained the same since
:ref:`rdata_flat`. However the next call to `opt` does cause a change.
Specifically, the call to `opt_dff` without the ``-nodffe -nosdff``
options is able to fold one of the `$mux` cells into the `$adff` to form an
`$adffe` cell; highlighted below:
Specifically, the call to `opt_dff` without the ``-nodffe -nosdff`` options is
able to fold one of the `$mux` cells into the `$adff` to form an `$adffe` cell;
highlighted below:
.. literalinclude:: /code_examples/fifo/fifo.out
:language: doscon
@ -433,8 +428,8 @@ The next two (new) commands are :doc:`/cmd/peepopt` and :doc:`/cmd/share`.
Neither of these affect our design, and they're explored in more detail in
:doc:`/using_yosys/synthesis/opt`, so let's skip over them. :yoscrypt:`techmap
-map +/cmp2lut.v -D LUT_WIDTH=4` optimizes certain comparison operators by
converting them to LUTs instead. The usage of `techmap` is explored
more in :doc:`/using_yosys/synthesis/techmap_synth`.
converting them to LUTs instead. The usage of `techmap` is explored more in
:doc:`/using_yosys/synthesis/techmap_synth`.
Our next command to run is
:doc:`/cmd/memory_dff`.
@ -451,9 +446,9 @@ Our next command to run is
``rdata`` output after `memory_dff`
As the title suggests, `memory_dff` has merged the output `$dff` into
the `$memrd` cell and converted it to a `$memrd_v2` (highlighted). This has
also connected the ``CLK`` port to the ``clk`` input as it is now a synchronous
As the title suggests, `memory_dff` has merged the output `$dff` into the
`$memrd` cell and converted it to a `$memrd_v2` (highlighted). This has also
connected the ``CLK`` port to the ``clk`` input as it is now a synchronous
memory read with appropriate enable (``EN=1'1``) and reset (``ARST=1'0`` and
``SRST=1'0``) inputs.
@ -466,12 +461,11 @@ memory read with appropriate enable (``EN=1'1``) and reset (``ARST=1'0`` and
Part 3
^^^^^^
The third part of the `synth_ice40` flow is a series of commands for
mapping to DSPs. By default, the iCE40 flow will not map to the hardware DSP
blocks and will only be performed if called with the ``-dsp`` flag:
:yoscrypt:`synth_ice40 -dsp`. While our example has nothing that could be
mapped to DSPs we can still take a quick look at the commands here and describe
what they do.
The third part of the `synth_ice40` flow is a series of commands for mapping to
DSPs. By default, the iCE40 flow will not map to the hardware DSP blocks and
will only be performed if called with the ``-dsp`` flag: :yoscrypt:`synth_ice40
-dsp`. While our example has nothing that could be mapped to DSPs we can still
take a quick look at the commands here and describe what they do.
.. literalinclude:: /cmd/synth_ice40.rst
:language: yoscrypt
@ -483,28 +477,26 @@ what they do.
:yoscrypt:`wreduce t:$mul` performs width reduction again, this time targetting
only cells of type `$mul`. :yoscrypt:`techmap -map +/mul2dsp.v -map
+/ice40/dsp_map.v ... -D DSP_NAME=$__MUL16X16` uses `techmap` to map
`$mul` cells to ``$__MUL16X16`` which are, in turn, mapped to the iCE40
``SB_MAC16``. Any multipliers which aren't compatible with conversion to
``$__MUL16X16`` are relabelled to ``$__soft_mul`` before `chtype`
changes them back to `$mul`.
+/ice40/dsp_map.v ... -D DSP_NAME=$__MUL16X16` uses `techmap` to map `$mul`
cells to ``$__MUL16X16`` which are, in turn, mapped to the iCE40 ``SB_MAC16``.
Any multipliers which aren't compatible with conversion to ``$__MUL16X16`` are
relabelled to ``$__soft_mul`` before `chtype` changes them back to `$mul`.
During the mul2dsp conversion, some of the intermediate signals are marked with
the attribute ``mul2dsp``. By calling :yoscrypt:`select a:mul2dsp` we restrict
the following commands to only operate on the cells and wires used for these
signals. `setattr` removes the now unnecessary ``mul2dsp`` attribute.
`opt_expr` we've already come across for const folding and simple
expression rewriting, the ``-fine`` option just enables more fine-grain
optimizations. Then we perform width reduction a final time and clear the
selection.
`opt_expr` we've already come across for const folding and simple expression
rewriting, the ``-fine`` option just enables more fine-grain optimizations.
Then we perform width reduction a final time and clear the selection.
.. todo:: ``ice40_dsp`` is pmgen
Finally we have `ice40_dsp`: similar to the `memory_dff`
command we saw in the previous section, this merges any surrounding registers
into the ``SB_MAC16`` cell. This includes not just the input/output registers,
but also pipeline registers and even a post-adder where applicable: turning a
multiply + add into a single multiply-accumulate.
Finally we have `ice40_dsp`: similar to the `memory_dff` command we saw in the
previous section, this merges any surrounding registers into the ``SB_MAC16``
cell. This includes not just the input/output registers, but also pipeline
registers and even a post-adder where applicable: turning a multiply + add into
a single multiply-accumulate.
.. seealso:: Advanced usage docs for
:doc:`/using_yosys/synthesis/techmap_synth`
@ -522,11 +514,10 @@ That brings us to the fourth and final part for the iCE40 synthesis flow:
:caption: ``coarse`` section (part 4)
:name: synth_coarse4
Where before each type of arithmetic operation had its own cell, e.g. `$add`,
we now want to extract these into `$alu` and `$macc` cells which can help
identify opportunities for reusing logic. We do this by running
`alumacc`, which we can see produce the following changes in our
example design:
Where before each type of arithmetic operation had its own cell, e.g. `$add`, we
now want to extract these into `$alu` and `$macc` cells which can help identify
opportunities for reusing logic. We do this by running `alumacc`, which we can
see produce the following changes in our example design:
.. literalinclude:: /code_examples/fifo/fifo.out
:language: doscon
@ -540,17 +531,17 @@ example design:
``rdata`` output after `alumacc`
Once these cells have been inserted, the call to `opt` can combine
cells which are now identical but may have been missed due to e.g. the
difference between `$add` and `$sub`.
Once these cells have been inserted, the call to `opt` can combine cells which
are now identical but may have been missed due to e.g. the difference between
`$add` and `$sub`.
The other new command in this part is :doc:`/cmd/memory`. `memory` is
another macro command which we examine in more detail in
The other new command in this part is :doc:`/cmd/memory`. `memory` is another
macro command which we examine in more detail in
:doc:`/using_yosys/synthesis/memory`. For this document, let us focus just on
the step most relevant to our example: `memory_collect`. Up until this
point, our memory reads and our memory writes have been totally disjoint cells;
operating on the same memory only in the abstract. `memory_collect`
combines all of the reads and writes for a memory block into a single cell.
the step most relevant to our example: `memory_collect`. Up until this point,
our memory reads and our memory writes have been totally disjoint cells;
operating on the same memory only in the abstract. `memory_collect` combines all
of the reads and writes for a memory block into a single cell.
.. figure:: /_images/code_examples/fifo/rdata_coarse.*
:class: width-helper invert-helper
@ -609,19 +600,19 @@ Mapping to hard memory blocks uses a combination of `memory_libmap` and
``rdata`` output after :ref:`map_ram`
The :ref:`map_ram` converts the generic `$mem_v2` into the iCE40
``SB_RAM40_4K`` (highlighted). We can also see the memory address has been
remapped, and the data bits have been reordered (or swizzled). There is also
now a `$mux` cell controlling the value of ``rdata``. In :ref:`fifo-v` we
wrote our memory as read-before-write, however the ``SB_RAM40_4K`` has undefined
behaviour when reading from and writing to the same address in the same cycle.
As a result, extra logic is added so that the generated circuit matches the
behaviour of the verilog. :ref:`no_rw_check` describes how we could change our
verilog to match our hardware instead.
The :ref:`map_ram` converts the generic `$mem_v2` into the iCE40 ``SB_RAM40_4K``
(highlighted). We can also see the memory address has been remapped, and the
data bits have been reordered (or swizzled). There is also now a `$mux` cell
controlling the value of ``rdata``. In :ref:`fifo-v` we wrote our memory as
read-before-write, however the ``SB_RAM40_4K`` has undefined behaviour when
reading from and writing to the same address in the same cycle. As a result,
extra logic is added so that the generated circuit matches the behaviour of the
verilog. :ref:`no_rw_check` describes how we could change our verilog to match
our hardware instead.
If we run `memory_libmap` under the `debug` command we can see
candidates which were identified for mapping, along with the costs of each and
what logic requires emulation.
If we run `memory_libmap` under the `debug` command we can see candidates which
were identified for mapping, along with the costs of each and what logic
requires emulation.
.. literalinclude:: /code_examples/fifo/fifo.libmap
:language: doscon
@ -667,11 +658,10 @@ into flip flops (the ``logic fallback``) with `memory_map`.
Arithmetic
^^^^^^^^^^
Uses `techmap` to map basic arithmetic logic to hardware. This sees
somewhat of an explosion in cells as multi-bit :cell:ref:`$mux` and `$adffe` are
replaced with single-bit `$_MUX_` and `$_DFFE_PP0P_` cells, while the
:cell:ref:`$alu` is replaced with primitive `$_OR_` and `$_NOT_` gates and a
`$lut` cell.
Uses `techmap` to map basic arithmetic logic to hardware. This sees somewhat of
an explosion in cells as multi-bit `$mux` and `$adffe` are replaced with
single-bit `$_MUX_` and `$_DFFE_PP0P_` cells, while the `$alu` is replaced with
primitive `$_OR_` and `$_NOT_` gates and a `$lut` cell.
.. literalinclude:: /cmd/synth_ice40.rst
:language: yoscrypt
@ -693,12 +683,12 @@ replaced with single-bit `$_MUX_` and `$_DFFE_PP0P_` cells, while the
Flip-flops
^^^^^^^^^^
Convert FFs to the types supported in hardware with `dfflegalize`, and
then use `techmap` to map them. In our example, this converts the
`$_DFFE_PP0P_` cells to ``SB_DFFER``.
Convert FFs to the types supported in hardware with `dfflegalize`, and then use
`techmap` to map them. In our example, this converts the `$_DFFE_PP0P_` cells
to ``SB_DFFER``.
We also run `simplemap` here to convert any remaining cells which could
not be mapped to hardware into gate-level primitives. This includes optimizing
We also run `simplemap` here to convert any remaining cells which could not be
mapped to hardware into gate-level primitives. This includes optimizing
`$_MUX_` cells where one of the inputs is a constant ``1'0``, replacing it
instead with an `$_AND_` cell.
@ -722,11 +712,10 @@ instead with an `$_AND_` cell.
LUTs
^^^^
`abc` and `techmap` are used to map LUTs; converting primitive
cell types to use `$lut` and ``SB_CARRY`` cells. Note that the iCE40 flow
uses `abc9` rather than `abc`. For more on what these do, and
what the difference between these two commands are, refer to
:doc:`/using_yosys/synthesis/abc`.
`abc` and `techmap` are used to map LUTs; converting primitive cell types to use
`$lut` and ``SB_CARRY`` cells. Note that the iCE40 flow uses `abc9` rather than
`abc`. For more on what these do, and what the difference between these two
commands are, refer to :doc:`/using_yosys/synthesis/abc`.
.. literalinclude:: /cmd/synth_ice40.rst
:language: yoscrypt
@ -742,8 +731,8 @@ what the difference between these two commands are, refer to
``rdata`` output after :ref:`map_luts`
Finally we use `techmap` to map the generic `$lut` cells to iCE40
``SB_LUT4`` cells.
Finally we use `techmap` to map the generic `$lut` cells to iCE40 ``SB_LUT4``
cells.
.. literalinclude:: /cmd/synth_ice40.rst
:language: yoscrypt
@ -801,28 +790,27 @@ The new commands here are:
- :doc:`/cmd/stat`, and
- :doc:`/cmd/blackbox`.
The output from `stat` is useful for checking resource utilization;
providing a list of cells used in the design and the number of each, as well as
the number of other resources used such as wires and processes. For this
design, the final call to `stat` should look something like the
following:
The output from `stat` is useful for checking resource utilization; providing a
list of cells used in the design and the number of each, as well as the number
of other resources used such as wires and processes. For this design, the final
call to `stat` should look something like the following:
.. literalinclude:: /code_examples/fifo/fifo.stat
:language: doscon
:start-at: yosys> stat -top fifo
Note that the :yoscrypt:`-top fifo` here is optional. `stat` will
automatically use the module with the ``top`` attribute set, which ``fifo`` was
when we called `hierarchy`. If no module is marked ``top``, then stats
will be shown for each module selected.
Note that the :yoscrypt:`-top fifo` here is optional. `stat` will automatically
use the module with the ``top`` attribute set, which ``fifo`` was when we called
`hierarchy`. If no module is marked ``top``, then stats will be shown for each
module selected.
The `stat` output is also useful as a kind of sanity-check: Since we
have already run `proc`, we wouldn't expect there to be any processes.
We also expect ``data`` to use hard memory; if instead of an ``SB_RAM40_4K`` saw
a high number of flip-flops being used we might suspect something was wrong.
The `stat` output is also useful as a kind of sanity-check: Since we have
already run `proc`, we wouldn't expect there to be any processes. We also expect
``data`` to use hard memory; if instead of an ``SB_RAM40_4K`` saw a high number
of flip-flops being used we might suspect something was wrong.
If we instead called `stat` immediately after :yoscrypt:`read_verilog
fifo.v` we would see something very different:
If we instead called `stat` immediately after :yoscrypt:`read_verilog fifo.v` we
would see something very different:
.. literalinclude:: /code_examples/fifo/fifo.stat
:language: doscon
@ -845,10 +833,10 @@ The iCE40 synthesis flow has the following output modes available:
As an example, if we called :yoscrypt:`synth_ice40 -top fifo -json fifo.json`,
our synthesized ``fifo`` design will be output as :file:`fifo.json`. We can
then read the design back into Yosys with `read_json`, but make sure
you use :yoscrypt:`design -reset` or open a new interactive terminal first. The
JSON output we get can also be loaded into `nextpnr`_ to do place and route; but
that is beyond the scope of this documentation.
then read the design back into Yosys with `read_json`, but make sure you use
:yoscrypt:`design -reset` or open a new interactive terminal first. The JSON
output we get can also be loaded into `nextpnr`_ to do place and route; but that
is beyond the scope of this documentation.
.. _nextpnr: https://github.com/YosysHQ/nextpnr

5
docs/source/getting_started/installation.rst
View File

@ -184,9 +184,8 @@ directories:
``passes/``
This directory contains a subdirectory for each pass or group of passes. For
example as of this writing the directory :file:`passes/hierarchy/` contains the
code for three passes: `hierarchy`, `submod`, and
`uniquify`.
example as of this writing the directory :file:`passes/hierarchy/` contains
the code for three passes: `hierarchy`, `submod`, and `uniquify`.
``techlibs/``
This directory contains simulation models and standard implementations for

56
docs/source/getting_started/scripting_intro.rst
View File

@ -61,24 +61,23 @@ already, let's take a look at some of those script files now.
:caption: A section of :file:`fifo.ys`, generating the images used for :ref:`addr_gen_example`
:name: fifo-ys
The first command there, :yoscrypt:`echo on`, uses `echo` to enable
command echoes on. This is how we generated the code listing for
The first command there, :yoscrypt:`echo on`, uses `echo` to enable command
echoes on. This is how we generated the code listing for
:ref:`hierarchy_output`. Turning command echoes on prints the ``yosys>
hierarchy -top addr_gen`` line, making the output look the same as if it were an
interactive terminal. :yoscrypt:`hierarchy -top addr_gen` is of course the
command we were demonstrating, including the output text and an image of the
design schematic after running it.
We briefly touched on `select` when it came up in
`synth_ice40`, but let's look at it more now.
We briefly touched on `select` when it came up in `synth_ice40`, but let's look
at it more now.
.. _select_intro:
Selections intro
^^^^^^^^^^^^^^^^
The `select` command is used to modify and view the list of selected
objects:
The `select` command is used to modify and view the list of selected objects:
.. literalinclude:: /code_examples/fifo/fifo.out
:language: doscon
@ -118,8 +117,8 @@ statement.
Many commands also support an optional ``[selection]`` argument which can be
used to override the currently selected objects. We could, for example, call
:yoscrypt:`clean addr_gen` to have `clean` operate on *just* the
``addr_gen`` module.
:yoscrypt:`clean addr_gen` to have `clean` operate on *just* the ``addr_gen``
module.
Detailed documentation of the select framework can be found under
:doc:`/using_yosys/more_scripting/selections` or in the command reference at
@ -130,11 +129,11 @@ Detailed documentation of the select framework can be found under
Displaying schematics
^^^^^^^^^^^^^^^^^^^^^
While the `select` command is very useful, sometimes nothing beats
being able to see a design for yourself. This is where `show` comes
in. Note that this document is just an introduction to the `show`
command, only covering the basics. For more information, including a guide on
what the different symbols represent, see :ref:`interactive_show` and the
While the `select` command is very useful, sometimes nothing beats being able to
see a design for yourself. This is where `show` comes in. Note that this
document is just an introduction to the `show` command, only covering the
basics. For more information, including a guide on what the different symbols
represent, see :ref:`interactive_show` and the
:doc:`/using_yosys/more_scripting/interactive_investigation` page.
.. figure:: /_images/code_examples/fifo/addr_gen_show.*
@ -145,8 +144,8 @@ what the different symbols represent, see :ref:`interactive_show` and the
.. note::
The `show` command requires a working installation of `GraphViz`_
and `xdot`_ for displaying the actual circuit diagrams.
The `show` command requires a working installation of `GraphViz`_ and `xdot`_
for displaying the actual circuit diagrams.
.. _GraphViz: http://www.graphviz.org/
.. _xdot: https://github.com/jrfonseca/xdot.py
@ -160,8 +159,8 @@ we see the following:
:start-at: -prefix addr_gen_show
:end-before: yosys> show
Calling `show` with :yoscrypt:`-format dot` tells it we want to output
a :file:`.dot` file rather than opening it for display. The :yoscrypt:`-prefix
Calling `show` with :yoscrypt:`-format dot` tells it we want to output a
:file:`.dot` file rather than opening it for display. The :yoscrypt:`-prefix
addr_gen_show` option indicates we want the file to be called
:file:`addr_gen_show.{*}`. Remember, we do this in :file:`fifo.ys` because we
need to store the image for displaying in the documentation you're reading. But
@ -207,21 +206,20 @@ the two ``PROC`` blocks. To achieve this highlight, we make use of the
Calling :yoscrypt:`show -color maroon3 @new_cells -color cornflowerblue p:* -notitle`
As described in the the `help` output for `show` (or by
clicking on the `show` link), colors are specified as :yoscrypt:`-color
<color> <object>`. Color names for the ``<color>`` portion can be found on the
`GraphViz color docs`_. Unlike the final `show` parameter which can
have be any selection string, the ``<object>`` part must be a single selection
expression or named selection. That means while we can use ``@new_cells``, we
couldn't use ``t:$eq t:$add``. In general, if a command lists ``[selection]``
as its final parameter it can be any selection string. Any selections that are
not the final parameter, such as those used in options, must be a single
expression instead.
As described in the the `help` output for `show` (or by clicking on the `show`
link), colors are specified as :yoscrypt:`-color <color> <object>`. Color names
for the ``<color>`` portion can be found on the `GraphViz color docs`_. Unlike
the final `show` parameter which can have be any selection string, the
``<object>`` part must be a single selection expression or named selection.
That means while we can use ``@new_cells``, we couldn't use ``t:$eq t:$add``.
In general, if a command lists ``[selection]`` as its final parameter it can be
any selection string. Any selections that are not the final parameter, such as
those used in options, must be a single expression instead.
.. _GraphViz color docs: https://graphviz.org/doc/info/colors
For all of the options available to `show`, check the command reference
at :doc:`/cmd/show`.
For all of the options available to `show`, check the command reference at
:doc:`/cmd/show`.
.. seealso:: :ref:`interactive_show` on the
:doc:`/using_yosys/more_scripting/interactive_investigation` page.

26
docs/source/introduction.rst
View File

@ -161,9 +161,9 @@ Benefits of open source HDL synthesis
- Cost (also applies to ``free as in free beer`` solutions):
Today the cost for a mask set in 180nm technology is far less than
the cost for the design tools needed to design the mask layouts. Open Source
ASIC flows are an important enabler for ASIC-level Open Source Hardware.
Today the cost for a mask set in 180nm technology is far less than the cost
for the design tools needed to design the mask layouts. Open Source ASIC flows
are an important enabler for ASIC-level Open Source Hardware.
- Availability and Reproducibility:
@ -171,21 +171,23 @@ Benefits of open source HDL synthesis
else can also use. Even if most universities have access to all major
commercial tools, you usually do not have easy access to the version that was
used in a research project a couple of years ago. With Open Source tools you
can even release the source code of the tool you have used alongside your data.
can even release the source code of the tool you have used alongside your
data.
- Framework:
Yosys is not only a tool. It is a framework that can be used as basis for other
developments, so researchers and hackers alike do not need to re-invent the
basic functionality. Extensibility was one of Yosys' design goals.
Yosys is not only a tool. It is a framework that can be used as basis for
other developments, so researchers and hackers alike do not need to re-invent
the basic functionality. Extensibility was one of Yosys' design goals.
- All-in-one:
Because of the framework characteristics of Yosys, an increasing number of features
become available in one tool. Yosys not only can be used for circuit synthesis but
also for formal equivalence checking, SAT solving, and for circuit analysis, to
name just a few other application domains. With proprietary software one needs to
learn a new tool for each of these applications.
Because of the framework characteristics of Yosys, an increasing number of
features become available in one tool. Yosys not only can be used for circuit
synthesis but also for formal equivalence checking, SAT solving, and for
circuit analysis, to name just a few other application domains. With
proprietary software one needs to learn a new tool for each of these
applications.
- Educational Tool:

219
docs/source/using_yosys/more_scripting/interactive_investigation.rst
View File

@ -13,9 +13,9 @@ A look at the show command
.. TODO:: merge into :doc:`/getting_started/scripting_intro` show section
This section explores the `show` command and explains the symbols used
in the circuit diagrams generated by it. The code used is included in the Yosys
code base under |code_examples/show|_.
This section explores the `show` command and explains the symbols used in the
circuit diagrams generated by it. The code used is included in the Yosys code
base under |code_examples/show|_.
.. |code_examples/show| replace:: :file:`docs/source/code_examples/show`
.. _code_examples/show: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/show
@ -32,11 +32,10 @@ will use to demonstrate the usage of `show` in a simple setting.
:name: example_v
The Yosys synthesis script we will be running is included as
:numref:`example_ys`. Note that `show` is called with the ``-pause``
option, that halts execution of the Yosys script until the user presses the
Enter key. Using :yoscrypt:`show -pause` also allows the user to enter an
interactive shell to further investigate the circuit before continuing
synthesis.
:numref:`example_ys`. Note that `show` is called with the ``-pause`` option,
that halts execution of the Yosys script until the user presses the Enter key.
Using :yoscrypt:`show -pause` also allows the user to enter an interactive shell
to further investigate the circuit before continuing synthesis.
.. literalinclude:: /code_examples/show/example_show.ys
:language: yoscrypt
@ -95,19 +94,19 @@ multiplexer and a d-type flip-flop, which brings us to the second diagram:
The Rhombus shape to the right is a dangling wire. (Wire nodes are only shown if
they are dangling or have "public" names, for example names assigned from the
Verilog input.) Also note that the design now contains two instances of a
``BUF``-node. These are artefacts left behind by the `proc` command. It
is quite usual to see such artefacts after calling commands that perform changes
in the design, as most commands only care about doing the transformation in the
least complicated way, not about cleaning up after them. The next call to
`clean` (or `opt`, which includes `clean` as one of
its operations) will clean up these artefacts. This operation is so common in
Yosys scripts that it can simply be abbreviated with the ``;;`` token, which
doubles as separator for commands. Unless one wants to specifically analyze this
artefacts left behind some operations, it is therefore recommended to always
call `clean` before calling `show`.
``BUF``-node. These are artefacts left behind by the `proc` command. It is quite
usual to see such artefacts after calling commands that perform changes in the
design, as most commands only care about doing the transformation in the least
complicated way, not about cleaning up after them. The next call to `clean` (or
`opt`, which includes `clean` as one of its operations) will clean up these
artefacts. This operation is so common in Yosys scripts that it can simply be
abbreviated with the ``;;`` token, which doubles as separator for commands.
Unless one wants to specifically analyze this artefacts left behind some
operations, it is therefore recommended to always call `clean` before calling
`show`.
In this script we directly call `opt` as the next step, which finally
leads us to the third diagram:
In this script we directly call `opt` as the next step, which finally leads us
to the third diagram:
.. figure:: /_images/code_examples/show/example_third.*
:class: width-helper invert-helper
@ -115,9 +114,9 @@ leads us to the third diagram:
Output of the third `show` command in :ref:`example_ys`
Here we see that the `opt` command not only has removed the artifacts
left behind by `proc`, but also determined correctly that it can remove
the first `$mux` cell without changing the behavior of the circuit.
Here we see that the `opt` command not only has removed the artifacts left
behind by `proc`, but also determined correctly that it can remove the first
`$mux` cell without changing the behavior of the circuit.
Break-out boxes for signal vectors
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@ -188,8 +187,8 @@ individual bits, resulting in an unnecessary complex diagram.
:class: width-helper invert-helper
:name: second_pitfall
Effects of `splitnets` command and of providing a cell library on
design in :numref:`first_pitfall`
Effects of `splitnets` command and of providing a cell library on design in
:numref:`first_pitfall`
.. literalinclude:: /code_examples/show/cmos.ys
:language: yoscrypt
@ -201,8 +200,8 @@ individual bits, resulting in an unnecessary complex diagram.
For :numref:`second_pitfall`, Yosys has been given a description of the cell
library as Verilog file containing blackbox modules. There are two ways to load
cell descriptions into Yosys: First the Verilog file for the cell library can be
passed directly to the `show` command using the ``-lib <filename>``
option. Secondly it is possible to load cell libraries into the design with the
passed directly to the `show` command using the ``-lib <filename>`` option.
Secondly it is possible to load cell libraries into the design with the
:yoscrypt:`read_verilog -lib <filename>` command. The second method has the
great advantage that the library only needs to be loaded once and can then be
used in all subsequent calls to the `show` command.
@ -216,19 +215,19 @@ module ports. Per default the command only operates on interior signals.
Miscellaneous notes
^^^^^^^^^^^^^^^^^^^
Per default the `show` command outputs a temporary dot file and
launches ``xdot`` to display it. The options ``-format``, ``-viewer`` and
``-prefix`` can be used to change format, viewer and filename prefix. Note that
the ``pdf`` and ``ps`` format are the only formats that support plotting
multiple modules in one run. The ``dot`` format can be used to output multiple
modules, however ``xdot`` will raise an error when trying to read them.
Per default the `show` command outputs a temporary dot file and launches
``xdot`` to display it. The options ``-format``, ``-viewer`` and ``-prefix`` can
be used to change format, viewer and filename prefix. Note that the ``pdf`` and
``ps`` format are the only formats that support plotting multiple modules in one
run. The ``dot`` format can be used to output multiple modules, however
``xdot`` will raise an error when trying to read them.
In densely connected circuits it is sometimes hard to keep track of the
individual signal wires. For these cases it can be useful to call
`show` with the ``-colors <integer>`` argument, which randomly assigns
colors to the nets. The integer (> 0) is used as seed value for the random color
assignments. Sometimes it is necessary it try some values to find an assignment
of colors that looks good.
individual signal wires. For these cases it can be useful to call `show` with
the ``-colors <integer>`` argument, which randomly assigns colors to the nets.
The integer (> 0) is used as seed value for the random color assignments.
Sometimes it is necessary it try some values to find an assignment of colors
that looks good.
The command :yoscrypt:`help show` prints a complete listing of all options
supported by the `show` command.
@ -244,10 +243,10 @@ relevant portions of the circuit.
In addition to *what* to display one also needs to carefully decide *when* to
display it, with respect to the synthesis flow. In general it is a good idea to
troubleshoot a circuit in the earliest state in which a problem can be
reproduced. So if, for example, the internal state before calling the
`techmap` command already fails to verify, it is better to troubleshoot
the coarse-grain version of the circuit before `techmap` than the
gate-level circuit after `techmap`.
reproduced. So if, for example, the internal state before calling the `techmap`
command already fails to verify, it is better to troubleshoot the coarse-grain
version of the circuit before `techmap` than the gate-level circuit after
`techmap`.
.. Note::
@ -260,18 +259,17 @@ Interactive navigation
^^^^^^^^^^^^^^^^^^^^^^
Once the right state within the synthesis flow for debugging the circuit has
been identified, it is recommended to simply add the `shell` command to
the matching place in the synthesis script. This command will stop the synthesis
at the specified moment and go to shell mode, where the user can interactively
been identified, it is recommended to simply add the `shell` command to the
matching place in the synthesis script. This command will stop the synthesis at
the specified moment and go to shell mode, where the user can interactively
enter commands.
For most cases, the shell will start with the whole design selected (i.e. when
the synthesis script does not already narrow the selection). The command
`ls` can now be used to create a list of all modules. The command
`cd` can be used to switch to one of the modules (type ``cd ..`` to
switch back). Now the `ls` command lists the objects within that
module. This is demonstrated below using :file:`example.v` from `A simple
circuit`_:
the synthesis script does not already narrow the selection). The command `ls`
can now be used to create a list of all modules. The command `cd` can be used to
switch to one of the modules (type ``cd ..`` to switch back). Now the `ls`
command lists the objects within that module. This is demonstrated below using
:file:`example.v` from `A simple circuit`_:
.. literalinclude:: /code_examples/show/example.out
:language: doscon
@ -280,11 +278,10 @@ circuit`_:
:caption: Output of `ls` and `cd` after running :file:`yosys example.v`
:name: lscd
When a module is selected using the `cd` command, all commands (with a
few exceptions, such as the ``read_`` and ``write_`` commands) operate only on
the selected module. This can also be useful for synthesis scripts where
different synthesis strategies should be applied to different modules in the
design.
When a module is selected using the `cd` command, all commands (with a few
exceptions, such as the ``read_`` and ``write_`` commands) operate only on the
selected module. This can also be useful for synthesis scripts where different
synthesis strategies should be applied to different modules in the design.
We can see that the cell names from :numref:`example_out` are just abbreviations
of the actual cell names, namely the part after the last dollar-sign. Most
@ -292,15 +289,14 @@ auto-generated names (the ones starting with a dollar sign) are rather long and
contains some additional information on the origin of the named object. But in
most cases those names can simply be abbreviated using the last part.
Usually all interactive work is done with one module selected using the
`cd` command. But it is also possible to work from the design-context
(``cd ..``). In this case all object names must be prefixed with
``<module_name>/``. For example ``a*/b*`` would refer to all objects whose names
start with ``b`` from all modules whose names start with ``a``.
Usually all interactive work is done with one module selected using the `cd`
command. But it is also possible to work from the design-context (``cd ..``). In
this case all object names must be prefixed with ``<module_name>/``. For example
``a*/b*`` would refer to all objects whose names start with ``b`` from all
modules whose names start with ``a``.
The `dump` command can be used to print all information about an
object. For example, calling :yoscrypt:`dump $2` after the :yoscrypt:`cd
example` above:
The `dump` command can be used to print all information about an object. For
example, calling :yoscrypt:`dump $2` after the :yoscrypt:`cd example` above:
.. literalinclude:: /code_examples/show/example.out
:language: RTLIL
@ -323,11 +319,10 @@ tools).
- The selection mechanism, especially patterns such as ``%ci`` and ``%co``, can
be used to figure out how parts of the design are connected.
- Commands such as `submod`, `expose`, and `splice`
can be used to transform the design into an equivalent design that is easier
to analyse.
- Commands such as `eval` and `sat` can be used to investigate
the behavior of the circuit.
- Commands such as `submod`, `expose`, and `splice` can be used to transform the
design into an equivalent design that is easier to analyse.
- Commands such as `eval` and `sat` can be used to investigate the behavior of
the circuit.
- :doc:`/cmd/show`.
- :doc:`/cmd/dump`.
- :doc:`/cmd/add` and :doc:`/cmd/delete` can be used to modify and reorganize a
@ -342,9 +337,9 @@ The code used is included in the Yosys code base under
Changing design hierarchy
^^^^^^^^^^^^^^^^^^^^^^^^^
Commands such as `flatten` and `submod` can be used to change
the design hierarchy, i.e. flatten the hierarchy or moving parts of a module to
a submodule. This has applications in synthesis scripts as well as in reverse
Commands such as `flatten` and `submod` can be used to change the design
hierarchy, i.e. flatten the hierarchy or moving parts of a module to a
submodule. This has applications in synthesis scripts as well as in reverse
engineering and analysis. An example using `submod` is shown below for
reorganizing a module in Yosys and checking the resulting circuit.
@ -388,10 +383,10 @@ Analyzing the resulting circuit with :doc:`/cmd/eval`:
Behavioral changes
^^^^^^^^^^^^^^^^^^
Commands such as `techmap` can be used to make behavioral changes to
the design, for example changing asynchronous resets to synchronous resets. This
has applications in design space exploration (evaluation of various
architectures for one circuit).
Commands such as `techmap` can be used to make behavioral changes to the design,
for example changing asynchronous resets to synchronous resets. This has
applications in design space exploration (evaluation of various architectures
for one circuit).
The following techmap map file replaces all positive-edge async reset flip-flops
with positive-edge sync reset flip-flops. The code is taken from the example
@ -448,8 +443,8 @@ Recall the ``memdemo`` design from :ref:`advanced_logic_cones`:
Because this produces a rather large circuit, it can be useful to split it into
smaller parts for viewing and working with. :numref:`submod` does exactly that,
utilising the `submod` command to split the circuit into three
sections: ``outstage``, ``selstage``, and ``scramble``.
utilising the `submod` command to split the circuit into three sections:
``outstage``, ``selstage``, and ``scramble``.
.. literalinclude:: /code_examples/selections/submod.ys
:language: yoscrypt
@ -481,9 +476,9 @@ below.
Evaluation of combinatorial circuits
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The `eval` command can be used to evaluate combinatorial circuits. As
an example, we will use the ``selstage`` subnet of ``memdemo`` which we found
above and is shown in :numref:`selstage`.
The `eval` command can be used to evaluate combinatorial circuits. As an
example, we will use the ``selstage`` subnet of ``memdemo`` which we found above
and is shown in :numref:`selstage`.
.. todo:: replace inline code
@ -526,21 +521,21 @@ The ``-table`` option can be used to create a truth table. For example:
Assumed undef (x) value for the following signals: \s2
Note that the `eval` command (as well as the `sat` command
discussed in the next sections) does only operate on flattened modules. It can
not analyze signals that are passed through design hierarchy levels. So the
`flatten` command must be used on modules that instantiate other
modules before these commands can be applied.
Note that the `eval` command (as well as the `sat` command discussed in the next
sections) does only operate on flattened modules. It can not analyze signals
that are passed through design hierarchy levels. So the `flatten` command must
be used on modules that instantiate other modules before these commands can be
applied.
Solving combinatorial SAT problems
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Often the opposite of the `eval` command is needed, i.e. the circuits
output is given and we want to find the matching input signals. For small
circuits with only a few input bits this can be accomplished by trying all
possible input combinations, as it is done by the ``eval -table`` command. For
larger circuits however, Yosys provides the `sat` command that uses a
`SAT`_ solver, `MiniSAT`_, to solve this kind of problems.
Often the opposite of the `eval` command is needed, i.e. the circuits output is
given and we want to find the matching input signals. For small circuits with
only a few input bits this can be accomplished by trying all possible input
combinations, as it is done by the ``eval -table`` command. For larger circuits
however, Yosys provides the `sat` command that uses a `SAT`_ solver, `MiniSAT`_,
to solve this kind of problems.
.. _SAT: http://en.wikipedia.org/wiki/Circuit_satisfiability
@ -551,9 +546,9 @@ larger circuits however, Yosys provides the `sat` command that uses a
While it is possible to perform model checking directly in Yosys, it
is highly recommended to use SBY or EQY for formal hardware verification.
The `sat` command works very similar to the `eval` command.
The main difference is that it is now also possible to set output values and
find the corresponding input values. For Example:
The `sat` command works very similar to the `eval` command. The main difference
is that it is now also possible to set output values and find the corresponding
input values. For Example:
.. todo:: replace inline code
@ -580,8 +575,8 @@ find the corresponding input values. For Example:
\s1 0 0 00
\s2 0 0 00
Note that the `sat` command supports signal names in both arguments to
the ``-set`` option. In the above example we used ``-set s1 s2`` to constraint
Note that the `sat` command supports signal names in both arguments to the
``-set`` option. In the above example we used ``-set s1 s2`` to constraint
``s1`` and ``s2`` to be equal. When more complex constraints are needed, a
wrapper circuit must be constructed that checks the constraints and signals if
the constraint was met using an extra output port, which then can be forced to a
@ -642,8 +637,8 @@ of course be to perform the test in 32 bits, for example by replacing ``p !=
a*b`` in the miter with ``p != {16'd0,a}b``, or by using a temporary variable
for the 32 bit product ``a*b``. But as 31 fits well into 8 bits (and as the
purpose of this document is to show off Yosys features) we can also simply force
the upper 8 bits of ``a`` and ``b`` to zero for the `sat` call, as is
done below.
the upper 8 bits of ``a`` and ``b`` to zero for the `sat` call, as is done
below.
.. todo:: replace inline code
@ -705,18 +700,18 @@ command:
sat -seq 6 -show y -show d -set-init-undef \
-max_undef -set-at 4 y 1 -set-at 5 y 2 -set-at 6 y 3
The ``-seq 6`` option instructs the `sat` command to solve a sequential
problem in 6 time steps. (Experiments with lower number of steps have show that
at least 3 cycles are necessary to bring the circuit in a state from which the
sequence 1, 2, 3 can be produced.)
The ``-seq 6`` option instructs the `sat` command to solve a sequential problem
in 6 time steps. (Experiments with lower number of steps have show that at least
3 cycles are necessary to bring the circuit in a state from which the sequence
1, 2, 3 can be produced.)
The ``-set-init-undef`` option tells the `sat` command to initialize
all registers to the undef (``x``) state. The way the ``x`` state is treated in
The ``-set-init-undef`` option tells the `sat` command to initialize all
registers to the undef (``x``) state. The way the ``x`` state is treated in
Verilog will ensure that the solution will work for any initial state.
The ``-max_undef`` option instructs the `sat` command to find a
solution with a maximum number of undefs. This way we can see clearly which
inputs bits are relevant to the solution.
The ``-max_undef`` option instructs the `sat` command to find a solution with a
maximum number of undefs. This way we can see clearly which inputs bits are
relevant to the solution.
Finally the three ``-set-at`` options add constraints for the ``y`` signal to
play the 1, 2, 3 sequence, starting with time step 4.
@ -807,7 +802,7 @@ is the only way of setting the ``s1`` and ``s2`` registers to a known value. The
input values for the other steps are a bit harder to work out manually, but the
SAT solver finds the correct solution in an instant.
There is much more to write about the `sat` command. For example, there
is a set of options that can be used to performs sequential proofs using
temporal induction :cite:p:`een2003temporal`. The command ``help sat`` can be
used to print a list of all options with short descriptions of their functions.
There is much more to write about the `sat` command. For example, there is a set
of options that can be used to performs sequential proofs using temporal
induction :cite:p:`een2003temporal`. The command ``help sat`` can be used to
print a list of all options with short descriptions of their functions.

3
docs/source/using_yosys/more_scripting/model_checking.rst
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@ -17,8 +17,7 @@ passes in Yosys.
Other applications include checking if a module conforms to interface standards.
The `sat` command in Yosys can be used to perform Symbolic Model
Checking.
The `sat` command in Yosys can be used to perform Symbolic Model Checking.
Checking techmap
~~~~~~~~~~~~~~~~

74
docs/source/using_yosys/more_scripting/selections.rst
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@ -9,31 +9,31 @@ The selection framework
.. todo:: reduce overlap with :doc:`/getting_started/scripting_intro` select section
The `select` command can be used to create a selection for subsequent
commands. For example:
The `select` command can be used to create a selection for subsequent commands.
For example:
.. code:: yoscrypt
select foobar # select the module foobar
delete # delete selected objects
Normally the `select` command overwrites a previous selection. The
commands :yoscrypt:`select -add` and :yoscrypt:`select -del` can be used to add
or remove objects from the current selection.
Normally the `select` command overwrites a previous selection. The commands
:yoscrypt:`select -add` and :yoscrypt:`select -del` can be used to add or remove
objects from the current selection.
The command :yoscrypt:`select -clear` can be used to reset the selection to the
default, which is a complete selection of everything in the current module.
This selection framework can also be used directly in many other commands.
Whenever a command has ``[selection]`` as last argument in its usage help, this
means that it will use the engine behind the `select` command to
evaluate additional arguments and use the resulting selection instead of the
selection created by the last `select` command.
means that it will use the engine behind the `select` command to evaluate
additional arguments and use the resulting selection instead of the selection
created by the last `select` command.
For example, the command `delete` will delete everything in the current
selection; while :yoscrypt:`delete foobar` will only delete the module foobar.
If no `select` command has been made, then the "current selection" will
be the whole design.
If no `select` command has been made, then the "current selection" will be the
whole design.
.. note:: Many of the examples on this page make use of the `show`
command to visually demonstrate the effect of selections. For a more
@ -59,8 +59,8 @@ Module and design context
^^^^^^^^^^^^^^^^^^^^^^^^^
Commands can be executed in *module/* or *design/* context. Until now, all
commands have been executed in design context. The `cd` command can be
used to switch to module context.
commands have been executed in design context. The `cd` command can be used to
switch to module context.
In module context, all commands only effect the active module. Objects in the
module are selected without the ``<module_name>/`` prefix. For example:
@ -91,7 +91,7 @@ Special patterns can be used to select by object property or type. For example:
a:foobar=42`
- select all modules with the attribute ``blabla`` set: :yoscrypt:`select
A:blabla`
- select all $add cells from the module foo: :yoscrypt:`select foo/t:$add`
- select all `$add` cells from the module foo: :yoscrypt:`select foo/t:$add`
A complete list of pattern expressions can be found in :doc:`/cmd/select`.
@ -101,12 +101,12 @@ Operations on selections
Combining selections
^^^^^^^^^^^^^^^^^^^^
The `select` command is actually much more powerful than it might seem
at first glance. When it is called with multiple arguments, each argument is
evaluated and pushed separately on a stack. After all arguments have been
processed it simply creates the union of all elements on the stack. So
:yoscrypt:`select t:$add a:foo` will select all `$add` cells and all objects
with the ``foo`` attribute set:
The `select` command is actually much more powerful than it might seem at first
glance. When it is called with multiple arguments, each argument is evaluated
and pushed separately on a stack. After all arguments have been processed it
simply creates the union of all elements on the stack. So :yoscrypt:`select
t:$add a:foo` will select all `$add` cells and all objects with the ``foo``
attribute set:
.. literalinclude:: /code_examples/selections/foobaraddsub.v
:caption: Test module for operations on selections
@ -220,11 +220,11 @@ The following sequence of diagrams demonstrates this step-wise expansion:
Output of :yoscrypt:`show prod %ci %ci %ci` on :numref:`sumprod`
Notice the subtle difference between :yoscrypt:`show prod %ci` and
:yoscrypt:`show prod %ci %ci`. Both images show the `$mul` cell driven by
some inputs ``$3_Y`` and ``c``. However it is not until the second image,
having called ``%ci`` the second time, that `show` is able to
distinguish between ``$3_Y`` being a wire and ``c`` being an input. We can see
this better with the `dump` command instead:
:yoscrypt:`show prod %ci %ci`. Both images show the `$mul` cell driven by some
inputs ``$3_Y`` and ``c``. However it is not until the second image, having
called ``%ci`` the second time, that `show` is able to distinguish between
``$3_Y`` being a wire and ``c`` being an input. We can see this better with the
`dump` command instead:
.. literalinclude:: /code_examples/selections/sumprod.out
:language: RTLIL
@ -241,8 +241,8 @@ be a bit dull. So there is a shortcut for that: the number of iterations can be
appended to the action. So for example the action ``%ci3`` is identical to
performing the ``%ci`` action three times.
The action ``%ci*`` performs the ``%ci`` action over and over again until it
has no effect anymore.
The action ``%ci*`` performs the ``%ci`` action over and over again until it has
no effect anymore.
.. _advanced_logic_cones:
@ -264,8 +264,8 @@ source repository.
:name: memdemo_src
:language: verilog
The script :file:`memdemo.ys` is used to generate the images included here. Let's
look at the first section:
The script :file:`memdemo.ys` is used to generate the images included here.
Let's look at the first section:
.. literalinclude:: /code_examples/selections/memdemo.ys
:caption: Synthesizing :ref:`memdemo_src`
@ -276,8 +276,8 @@ look at the first section:
This loads :numref:`memdemo_src` and synthesizes the included module. Note that
this code can be copied and run directly in a Yosys command line session,
provided :file:`memdemo.v` is in the same directory. We can now change to the
``memdemo`` module with ``cd memdemo``, and call `show` to see the
diagram in :numref:`memdemo_00`.
``memdemo`` module with ``cd memdemo``, and call `show` to see the diagram in
:numref:`memdemo_00`.
.. figure:: /_images/code_examples/selections/memdemo_00.*
:class: width-helper invert-helper
@ -371,8 +371,8 @@ selection instead of overwriting it.
select -del reg_42 # but not this one
select -add state %ci # and add more stuff
Within a select expression the token ``%`` can be used to push the previous selection
on the stack.
Within a select expression the token ``%`` can be used to push the previous
selection on the stack.
.. code:: yoscrypt
@ -387,16 +387,16 @@ Storing and recalling selections
The current selection can be stored in memory with the command ``select -set
<name>``. It can later be recalled using ``select @<name>``. In fact, the
``@<name>`` expression pushes the stored selection on the stack maintained by
the `select` command. So for example :yoscrypt:`select @foo @bar %i`
will select the intersection between the stored selections ``foo`` and ``bar``.
the `select` command. So for example :yoscrypt:`select @foo @bar %i` will select
the intersection between the stored selections ``foo`` and ``bar``.
In larger investigation efforts it is highly recommended to maintain a script
that sets up relevant selections, so they can easily be recalled, for example
when Yosys needs to be re-run after a design or source code change.
The `history` command can be used to list all recent interactive
commands. This feature can be useful for creating such a script from the
commands used in an interactive session.
The `history` command can be used to list all recent interactive commands. This
feature can be useful for creating such a script from the commands used in an
interactive session.
Remember that select expressions can also be used directly as arguments to most
commands. Some commands also accept a single select argument to some options. In

11
docs/source/using_yosys/synthesis/abc.rst
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@ -10,13 +10,12 @@ fine-grained optimisation and LUT mapping.
Yosys has two different commands, which both use this logic toolbox, but use it
in different ways.
The `abc` pass can be used for both ASIC (e.g. :yoscrypt:`abc
-liberty`) and FPGA (:yoscrypt:`abc -lut`) mapping, but this page will focus on
FPGA mapping.
The `abc` pass can be used for both ASIC (e.g. :yoscrypt:`abc -liberty`) and
FPGA (:yoscrypt:`abc -lut`) mapping, but this page will focus on FPGA mapping.
The `abc9` pass generally provides superior mapping quality due to
being aware of combination boxes and DFF and LUT timings, giving it a more
global view of the mapping problem.
The `abc9` pass generally provides superior mapping quality due to being aware
of combination boxes and DFF and LUT timings, giving it a more global view of
the mapping problem.
.. _ABC: https://github.com/berkeley-abc/abc

8
docs/source/using_yosys/synthesis/cell_libs.rst
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@ -98,8 +98,8 @@ our internal cell library will be mapped to:
:name: mycells-lib
:caption: :file:`mycells.lib`
Recall that the Yosys built-in logic gate types are `$_NOT_`, `$_AND_`,
`$_OR_`, `$_XOR_`, and `$_MUX_` with an assortment of dff memory types.
Recall that the Yosys built-in logic gate types are `$_NOT_`, `$_AND_`, `$_OR_`,
`$_XOR_`, and `$_MUX_` with an assortment of dff memory types.
:ref:`mycells-lib` defines our target cells as ``BUF``, ``NOT``, ``NAND``,
``NOR``, and ``DFF``. Mapping between these is performed with the commands
`dfflibmap` and `abc` as follows:
@ -117,8 +117,8 @@ The final version of our ``counter`` module looks like this:
``counter`` after hardware cell mapping
Before finally being output as a verilog file with `write_verilog`,
which can then be loaded into another tool:
Before finally being output as a verilog file with `write_verilog`, which can
then be loaded into another tool:
.. literalinclude:: /code_examples/intro/counter.ys
:language: yoscrypt

28
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@ -1,12 +1,12 @@
The extract pass
----------------
- Like the `techmap` pass, the `extract` pass is called with a
map file. It compares the circuits inside the modules of the map file with the
design and looks for sub-circuits in the design that match any of the modules
in the map file.
- If a match is found, the `extract` pass will replace the matching
subcircuit with an instance of the module from the map file.
- Like the `techmap` pass, the `extract` pass is called with a map file. It
compares the circuits inside the modules of the map file with the design and
looks for sub-circuits in the design that match any of the modules in the map
file.
- If a match is found, the `extract` pass will replace the matching subcircuit
with an instance of the module from the map file.
- In a way the `extract` pass is the inverse of the techmap pass.
.. todo:: add/expand supporting text, also mention custom pattern matching and
@ -68,23 +68,23 @@ The wrap-extract-unwrap method
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Often a coarse-grain element has a constant bit-width, but can be used to
implement operations with a smaller bit-width. For example, a 18x25-bit multiplier
can also be used to implement 16x20-bit multiplication.
implement operations with a smaller bit-width. For example, a 18x25-bit
multiplier can also be used to implement 16x20-bit multiplication.
A way of mapping such elements in coarse grain synthesis is the
wrap-extract-unwrap method:
wrap
Identify candidate-cells in the circuit and wrap them in a cell with a
constant wider bit-width using `techmap`. The wrappers use the same
parameters as the original cell, so the information about the original width
of the ports is preserved. Then use the `connwrappers` command to
connect up the bit-extended in- and outputs of the wrapper cells.
constant wider bit-width using `techmap`. The wrappers use the same parameters
as the original cell, so the information about the original width of the ports
is preserved. Then use the `connwrappers` command to connect up the
bit-extended in- and outputs of the wrapper cells.
extract
Now all operations are encoded using the same bit-width as the coarse grain
element. The `extract` command can be used to replace circuits with
cells of the target architecture.
element. The `extract` command can be used to replace circuits with cells of
the target architecture.
unwrap
The remaining wrapper cell can be unwrapped using `techmap`.

31
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@ -25,9 +25,8 @@ following description:
- Does not already have the ``\fsm_encoding`` attribute.
- Is not an output of the containing module.
- Is driven by single `$dff` or `$adff` cell.
- The ``\D``-Input of this `$dff` or `$adff` cell is driven by a
multiplexer tree that only has constants or the old state value on its
leaves.
- The ``\D``-Input of this `$dff` or `$adff` cell is driven by a multiplexer
tree that only has constants or the old state value on its leaves.
- The state value is only used in the said multiplexer tree or by simple
relational cells that compare the state value to a constant (usually `$eq`
cells).
@ -87,8 +86,8 @@ given set of result signals using a set of signal-value assignments. It can also
be passed a list of stop-signals that abort the ConstEval algorithm if the value
of a stop-signal is needed in order to calculate the result signals.
The `fsm_extract` pass uses the ConstEval class in the following way to
create a transition table. For each state:
The `fsm_extract` pass uses the ConstEval class in the following way to create a
transition table. For each state:
1. Create a ConstEval object for the module containing the FSM
2. Add all control inputs to the list of stop signals
@ -108,13 +107,12 @@ drivers for the control outputs are disconnected.
FSM optimization
~~~~~~~~~~~~~~~~
The `fsm_opt` pass performs basic optimizations on `$fsm` cells (not
including state recoding). The following optimizations are performed (in this
order):
The `fsm_opt` pass performs basic optimizations on `$fsm` cells (not including
state recoding). The following optimizations are performed (in this order):
- Unused control outputs are removed from the `$fsm` cell. The attribute
``\unused_bits`` (that is usually set by the `opt_clean` pass) is
used to determine which control outputs are unused.
``\unused_bits`` (that is usually set by the `opt_clean` pass) is used to
determine which control outputs are unused.
- Control inputs that are connected to the same driver are merged.
@ -134,11 +132,10 @@ order):
FSM recoding
~~~~~~~~~~~~
The `fsm_recode` pass assigns new bit pattern to the states. Usually
this also implies a change in the width of the state signal. At the moment of
this writing only one-hot encoding with all-zero for the reset state is
supported.
The `fsm_recode` pass assigns new bit pattern to the states. Usually this also
implies a change in the width of the state signal. At the moment of this writing
only one-hot encoding with all-zero for the reset state is supported.
The `fsm_recode` pass can also write a text file with the changes
performed by it that can be used when verifying designs synthesized by Yosys
using Synopsys Formality.
The `fsm_recode` pass can also write a text file with the changes performed by
it that can be used when verifying designs synthesized by Yosys using Synopsys
Formality.

15
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@ -8,17 +8,16 @@ coarse-grain optimizations before being mapped to hard blocks and fine-grain
cells. Most commands in Yosys will target either coarse-grain representation or
fine-grain representation, with only a select few compatible with both states.
Commands such as `proc`, `fsm`, and `memory` rely on
the additional information in the coarse-grain representation, along with a
number of optimizations such as `wreduce`, `share`, and
`alumacc`. `opt` provides optimizations which are useful in
both states, while `techmap` is used to convert coarse-grain cells
to the corresponding fine-grain representation.
Commands such as `proc`, `fsm`, and `memory` rely on the additional information
in the coarse-grain representation, along with a number of optimizations such as
`wreduce`, `share`, and `alumacc`. `opt` provides optimizations which are
useful in both states, while `techmap` is used to convert coarse-grain cells to
the corresponding fine-grain representation.
Single-bit cells (logic gates, FFs) as well as LUTs, half-adders, and
full-adders make up the bulk of the fine-grain representation and are necessary
for commands such as `abc`\ /`abc9`, `simplemap`,
`dfflegalize`, and `memory_map`.
for commands such as `abc`\ /`abc9`, `simplemap`, `dfflegalize`, and
`memory_map`.
.. toctree::
:maxdepth: 3

208
docs/source/using_yosys/synthesis/memory.rst
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@ -5,10 +5,10 @@ The `memory` command
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
In the RTL netlist, memory reads and writes are individual cells. This makes
consolidating the number of ports for a memory easier. The `memory`
pass transforms memories to an implementation. Per default that is logic for
address decoders and registers. It also is a macro command that calls the other
common ``memory_*`` passes in a sensible order:
consolidating the number of ports for a memory easier. The `memory` pass
transforms memories to an implementation. Per default that is logic for address
decoders and registers. It also is a macro command that calls the other common
``memory_*`` passes in a sensible order:
.. literalinclude:: /code_examples/macro_commands/memory.ys
:language: yoscrypt
@ -22,11 +22,11 @@ Some quick notes:
- `memory_dff` merges registers into the memory read- and write cells.
- `memory_collect` collects all read and write cells for a memory and
transforms them into one multi-port memory cell.
- `memory_map` takes the multi-port memory cell and transforms it to
address decoder logic and registers.
- `memory_map` takes the multi-port memory cell and transforms it to address
decoder logic and registers.
For more information about `memory`, such as disabling certain sub
commands, see :doc:`/cmd/memory`.
For more information about `memory`, such as disabling certain sub commands, see
:doc:`/cmd/memory`.
Example
-------
@ -75,20 +75,20 @@ For example:
techmap -map my_memory_map.v
memory_map
`memory_libmap` attempts to convert memory cells (`$mem_v2` etc) into
hardware supported memory using a provided library (:file:`my_memory_map.txt` in the
`memory_libmap` attempts to convert memory cells (`$mem_v2` etc) into hardware
supported memory using a provided library (:file:`my_memory_map.txt` in the
example above). Where necessary, emulation logic is added to ensure functional
equivalence before and after this conversion. :yoscrypt:`techmap -map
my_memory_map.v` then uses `techmap` to map to hardware primitives. Any
leftover memory cells unable to be converted are then picked up by
`memory_map` and mapped to DFFs and address decoders.
my_memory_map.v` then uses `techmap` to map to hardware primitives. Any leftover
memory cells unable to be converted are then picked up by `memory_map` and
mapped to DFFs and address decoders.
.. note::
More information about what mapping options are available and associated
costs of each can be found by enabling debug outputs. This can be done with
the `debug` command, or by using the ``-g`` flag when calling Yosys
to globally enable debug messages.
the `debug` command, or by using the ``-g`` flag when calling Yosys to
globally enable debug messages.
For more on the lib format for `memory_libmap`, see
`passes/memory/memlib.md
@ -110,13 +110,15 @@ Notes
Memory kind selection
~~~~~~~~~~~~~~~~~~~~~
The memory inference code will automatically pick target memory primitive based on memory geometry
and features used. Depending on the target, there can be up to four memory primitive classes
available for selection:
The memory inference code will automatically pick target memory primitive based
on memory geometry and features used. Depending on the target, there can be up
to four memory primitive classes available for selection:
- FF RAM (aka logic): no hardware primitive used, memory lowered to a bunch of FFs and multiplexers
- FF RAM (aka logic): no hardware primitive used, memory lowered to a bunch of
FFs and multiplexers
- Can handle arbitrary number of write ports, as long as all write ports are in the same clock domain
- Can handle arbitrary number of write ports, as long as all write ports are
in the same clock domain
- Can handle arbitrary number and kind of read ports
- LUT RAM (aka distributed RAM): uses LUT storage as RAM
@ -131,7 +133,8 @@ available for selection:
- Supported on basically all FPGAs
- Supports only synchronous reads
- Two ports with separate clocks
- Usually supports true dual port (with notable exception of ice40 that only supports SDP)
- Usually supports true dual port (with notable exception of ice40 that only
supports SDP)
- Usually supports asymmetric memories and per-byte write enables
- Several kilobits in size
@ -155,19 +158,22 @@ available for selection:
- Two ports, both with mutually exclusive synchronous read and write
- Single clock
- Will not be automatically selected by memory inference code, needs explicit opt-in via
ram_style attribute
- Will not be automatically selected by memory inference code, needs explicit
opt-in via ram_style attribute
In general, you can expect the automatic selection process to work roughly like this:
In general, you can expect the automatic selection process to work roughly like
this:
- If any read port is asynchronous, only LUT RAM (or FF RAM) can be used.
- If there is more than one write port, only block RAM can be used, and this needs to be a
hardware-supported true dual port pattern
- If there is more than one write port, only block RAM can be used, and this
needs to be a hardware-supported true dual port pattern
- … unless all write ports are in the same clock domain, in which case FF RAM can also be used,
but this is generally not what you want for anything but really small memories
- … unless all write ports are in the same clock domain, in which case FF RAM
can also be used, but this is generally not what you want for anything but
really small memories
- Otherwise, either FF RAM, LUT RAM, or block RAM will be used, depending on memory size
- Otherwise, either FF RAM, LUT RAM, or block RAM will be used, depending on
memory size
This process can be overridden by attaching a ram_style attribute to the memory:
@ -178,15 +184,17 @@ This process can be overridden by attaching a ram_style attribute to the memory:
It is an error if this override cannot be realized for the given target.
Many alternate spellings of the attribute are also accepted, for compatibility with other software.
Many alternate spellings of the attribute are also accepted, for compatibility
with other software.
Initial data
~~~~~~~~~~~~
Most FPGA targets support initializing all kinds of memory to user-provided values. If explicit
initialization is not used the initial memory value is undefined. Initial data can be provided by
either initial statements writing memory cells one by one of ``$readmemh`` or ``$readmemb`` system
tasks. For an example pattern, see `sr_init`_.
Most FPGA targets support initializing all kinds of memory to user-provided
values. If explicit initialization is not used the initial memory value is
undefined. Initial data can be provided by either initial statements writing
memory cells one by one of ``$readmemh`` or ``$readmemb`` system tasks. For an
example pattern, see `sr_init`_.
.. _wbe:
@ -194,12 +202,13 @@ Write port with byte enables
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Byte enables can be used with any supported pattern
- To ensure that multiple writes will be merged into one port, they need to have disjoint bit
ranges, have the same address, and the same clock
- Any write enable granularity will be accepted (down to per-bit write enables), but using smaller
granularity than natively supported by the target is very likely to be inefficient (eg. using
4-bit bytes on ECP5 will result in either padding the bytes with 5 dummy bits to native 9-bit
units or splitting the RAM into two block RAMs)
- To ensure that multiple writes will be merged into one port, they need to have
disjoint bit ranges, have the same address, and the same clock
- Any write enable granularity will be accepted (down to per-bit write enables),
but using smaller granularity than natively supported by the target is very
likely to be inefficient (eg. using 4-bit bytes on ECP5 will result in either
padding the bytes with 5 dummy bits to native 9-bit units or splitting the RAM
into two block RAMs)
.. code:: verilog
@ -240,7 +249,8 @@ Synchronous SDP with clock domain crossing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Will result in block RAM or LUT RAM depending on size
- No behavior guarantees in case of simultaneous read and write to the same address
- No behavior guarantees in case of simultaneous read and write to the same
address
.. code:: verilog
@ -261,9 +271,9 @@ Synchronous SDP read first
- The read and write parts can be in the same or different processes.
- Will result in block RAM or LUT RAM depending on size
- As long as the same clock is used for both, yosys will ensure read-first behavior. This may
require extra circuitry on some targets for block RAM. If this is not necessary, use one of the
patterns below.
- As long as the same clock is used for both, yosys will ensure read-first
behavior. This may require extra circuitry on some targets for block RAM. If
this is not necessary, use one of the patterns below.
.. code:: verilog
@ -281,8 +291,8 @@ Synchronous SDP read first
Synchronous SDP with undefined collision behavior
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Like above, but the read value is undefined when read and write ports target the same address in
the same cycle
- Like above, but the read value is undefined when read and write ports target
the same address in the same cycle
.. code:: verilog
@ -322,8 +332,8 @@ Synchronous SDP with write-first behavior
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Will result in block RAM or LUT RAM depending on size
- May use additional circuitry for block RAM if write-first is not natively supported. Will always
use additional circuitry for LUT RAM.
- May use additional circuitry for block RAM if write-first is not natively
supported. Will always use additional circuitry for LUT RAM.
.. code:: verilog
@ -343,7 +353,8 @@ Synchronous SDP with write-first behavior
Synchronous SDP with write-first behavior (alternate pattern)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- This pattern is supported for compatibility, but is much less flexible than the above
- This pattern is supported for compatibility, but is much less flexible than
the above
.. code:: verilog
@ -378,8 +389,10 @@ Synchronous single-port RAM with mutually exclusive read/write
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Will result in single-port block RAM or LUT RAM depending on size
- This is the correct pattern to infer ice40 SPRAM (with manual ram_style selection)
- On targets that don't support read/write block RAM ports (eg. ice40), will result in SDP block RAM instead
- This is the correct pattern to infer ice40 SPRAM (with manual ram_style
selection)
- On targets that don't support read/write block RAM ports (eg. ice40), will
result in SDP block RAM instead
- For block RAM, will use "NO_CHANGE" mode if available
.. code:: verilog
@ -396,12 +409,14 @@ Synchronous single-port RAM with mutually exclusive read/write
Synchronous single-port RAM with read-first behavior
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Will only result in single-port block RAM when read-first behavior is natively supported;
otherwise, SDP RAM with additional circuitry will be used
- Many targets (Xilinx, ECP5, …) can only natively support read-first/write-first single-port RAM
(or TDP RAM) where the write_enable signal implies the read_enable signal (ie. can never write
without reading). The memory inference code will run a simple SAT solver on the control signals to
determine if this is the case, and insert emulation circuitry if it cannot be easily proven.
- Will only result in single-port block RAM when read-first behavior is natively
supported; otherwise, SDP RAM with additional circuitry will be used
- Many targets (Xilinx, ECP5, …) can only natively support
read-first/write-first single-port RAM (or TDP RAM) where the write_enable
signal implies the read_enable signal (ie. can never write without reading).
The memory inference code will run a simple SAT solver on the control signals
to determine if this is the case, and insert emulation circuitry if it cannot
be easily proven.
.. code:: verilog
@ -418,7 +433,8 @@ Synchronous single-port RAM with write-first behavior
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Will result in single-port block RAM or LUT RAM when supported
- Block RAMs will require extra circuitry if write-first behavior not natively supported
- Block RAMs will require extra circuitry if write-first behavior not natively
supported
.. code:: verilog
@ -440,8 +456,8 @@ Synchronous read port with initial value
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Initial read port values can be combined with any other supported pattern
- If block RAM is used and initial read port values are not natively supported by the target, small
emulation circuit will be inserted
- If block RAM is used and initial read port values are not natively supported
by the target, small emulation circuit will be inserted
.. code:: verilog
@ -459,10 +475,11 @@ Synchronous read port with initial value
Read register reset patterns
----------------------------
Resets can be combined with any other supported pattern (except that synchronous reset and
asynchronous reset cannot both be used on a single read port). If block RAM is used and the
selected reset (synchronous or asynchronous) is used but not natively supported by the target, small
emulation circuitry will be inserted.
Resets can be combined with any other supported pattern (except that synchronous
reset and asynchronous reset cannot both be used on a single read port). If
block RAM is used and the selected reset (synchronous or asynchronous) is used
but not natively supported by the target, small emulation circuitry will be
inserted.
Synchronous reset, reset priority over enable
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@ -520,22 +537,26 @@ Synchronous read port with asynchronous reset
Asymmetric memory patterns
--------------------------
To construct an asymmetric memory (memory with read/write ports of differing widths):
To construct an asymmetric memory (memory with read/write ports of differing
widths):
- Declare the memory with the width of the narrowest intended port
- Split all wide ports into multiple narrow ports
- To ensure the wide ports will be correctly merged:
- For the address, use a concatenation of actual address in the high bits and a constant in the
low bits
- Ensure the actual address is identical for all ports belonging to the wide port
- For the address, use a concatenation of actual address in the high bits and
a constant in the low bits
- Ensure the actual address is identical for all ports belonging to the wide
port
- Ensure that clock is identical
- For read ports, ensure that enable/reset signals are identical (for write ports, the enable
signal may vary — this will result in using the byte enable functionality)
- For read ports, ensure that enable/reset signals are identical (for write
ports, the enable signal may vary — this will result in using the byte
enable functionality)
Asymmetric memory is supported on all targets, but may require emulation circuitry where not
natively supported. Note that when the memory is larger than the underlying block RAM primitive,
hardware asymmetric memory support is likely not to be used even if present as it is more expensive.
Asymmetric memory is supported on all targets, but may require emulation
circuitry where not natively supported. Note that when the memory is larger
than the underlying block RAM primitive, hardware asymmetric memory support is
likely not to be used even if present as it is more expensive.
.. _wide_sr:
@ -615,20 +636,25 @@ Wide write port
True dual port (TDP) patterns
-----------------------------
- Many different variations of true dual port memory can be created by combining two single-port RAM
patterns on the same memory
- When TDP memory is used, memory inference code has much less maneuver room to create requested
semantics compared to individual single-port patterns (which can end up lowered to SDP memory
where necessary) — supported patterns depend strongly on the target
- In particular, when both ports have the same clock, it's likely that "undefined collision" mode
needs to be manually selected to enable TDP memory inference
- The examples below are non-exhaustive — many more combinations of port types are possible
- Note: if two write ports are in the same process, this defines a priority relation between them
(if both ports are active in the same clock, the later one wins). On almost all targets, this will
result in a bit of extra circuitry to ensure the priority semantics. If this is not what you want,
put them in separate processes.
- Many different variations of true dual port memory can be created by combining
two single-port RAM patterns on the same memory
- When TDP memory is used, memory inference code has much less maneuver room to
create requested semantics compared to individual single-port patterns (which
can end up lowered to SDP memory where necessary) — supported patterns depend
strongly on the target
- In particular, when both ports have the same clock, it's likely that
"undefined collision" mode needs to be manually selected to enable TDP memory
inference
- The examples below are non-exhaustive — many more combinations of port types
are possible
- Note: if two write ports are in the same process, this defines a priority
relation between them (if both ports are active in the same clock, the later
one wins). On almost all targets, this will result in a bit of extra circuitry
to ensure the priority semantics. If this is not what you want, put them in
separate processes.
- Priority is not supported when using the verific front end and any priority semantics are ignored.
- Priority is not supported when using the verific front end and any priority
semantics are ignored.
TDP with different clocks, exclusive read/write
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@ -654,7 +680,8 @@ TDP with different clocks, exclusive read/write
TDP with same clock, read-first behavior
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- This requires hardware inter-port read-first behavior, and will only work on some targets (Xilinx, Nexus)
- This requires hardware inter-port read-first behavior, and will only work on
some targets (Xilinx, Nexus)
.. code:: verilog
@ -677,9 +704,10 @@ TDP with same clock, read-first behavior
TDP with multiple read ports
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- The combination of a single write port with an arbitrary amount of read ports is supported on all
targets — if a multi-read port primitive is available (like Xilinx RAM64M), it'll be used as
appropriate. Otherwise, the memory will be automatically split into multiple primitives.
- The combination of a single write port with an arbitrary amount of read ports
is supported on all targets — if a multi-read port primitive is available
(like Xilinx RAM64M), it'll be used as appropriate. Otherwise, the memory
will be automatically split into multiple primitives.
.. code:: verilog

82
docs/source/using_yosys/synthesis/opt.rst
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@ -9,9 +9,9 @@ This chapter outlines these optimizations.
The `opt` macro command
--------------------------------
The Yosys pass `opt` runs a number of simple optimizations. This
includes removing unused signals and cells and const folding. It is recommended
to run this pass after each major step in the synthesis script. As listed in
The Yosys pass `opt` runs a number of simple optimizations. This includes
removing unused signals and cells and const folding. It is recommended to run
this pass after each major step in the synthesis script. As listed in
:doc:`/cmd/opt`, this macro command calls the following ``opt_*`` commands:
.. literalinclude:: /code_examples/macro_commands/opt.ys
@ -69,17 +69,17 @@ undef.
The last two lines simply replace an `$_AND_` gate with one constant-1 input
with a buffer.
Besides this basic const folding the `opt_expr` pass can replace 1-bit
wide `$eq` and `$ne` cells with buffers or not-gates if one input is
constant. Equality checks may also be reduced in size if there are redundant
bits in the arguments (i.e. bits which are constant on both inputs). This can,
for example, result in a 32-bit wide constant like ``255`` being reduced to the
8-bit value of ``8'11111111`` if the signal being compared is only 8-bit as in
Besides this basic const folding the `opt_expr` pass can replace 1-bit wide
`$eq` and `$ne` cells with buffers or not-gates if one input is constant.
Equality checks may also be reduced in size if there are redundant bits in the
arguments (i.e. bits which are constant on both inputs). This can, for example,
result in a 32-bit wide constant like ``255`` being reduced to the 8-bit value
of ``8'11111111`` if the signal being compared is only 8-bit as in
:ref:`addr_gen_clean` of :doc:`/getting_started/example_synth`.
The `opt_expr` pass is very conservative regarding optimizing `$mux`
cells, as these cells are often used to model decision-trees and breaking these
trees can interfere with other optimizations.
The `opt_expr` pass is very conservative regarding optimizing `$mux` cells, as
these cells are often used to model decision-trees and breaking these trees can
interfere with other optimizations.
.. literalinclude:: /code_examples/opt/opt_expr.ys
:language: Verilog
@ -100,9 +100,9 @@ identifies cells with identical inputs and replaces them with a single instance
of the cell.
The option ``-nomux`` can be used to disable resource sharing for multiplexer
cells (`$mux` and `$pmux`.) This can be useful as it prevents multiplexer
trees to be merged, which might prevent `opt_muxtree` to identify
possible optimizations.
cells (`$mux` and `$pmux`.) This can be useful as it prevents multiplexer trees
to be merged, which might prevent `opt_muxtree` to identify possible
optimizations.
.. literalinclude:: /code_examples/opt/opt_merge.ys
:language: Verilog
@ -128,9 +128,9 @@ Consider the following simple example:
:caption: example verilog for demonstrating `opt_muxtree`
The output can never be ``c``, as this would require ``a`` to be 1 for the outer
multiplexer and 0 for the inner multiplexer. The `opt_muxtree` pass
detects this contradiction and replaces the inner multiplexer with a constant 1,
yielding the logic for ``y = a ? b : d``.
multiplexer and 0 for the inner multiplexer. The `opt_muxtree` pass detects this
contradiction and replaces the inner multiplexer with a constant 1, yielding the
logic for ``y = a ? b : d``.
.. figure:: /_images/code_examples/opt/opt_muxtree.*
:class: width-helper invert-helper
@ -141,9 +141,9 @@ Simplifying large MUXes and AND/OR gates - `opt_reduce`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This is a simple optimization pass that identifies and consolidates identical
input bits to `$reduce_and` and `$reduce_or` cells. It also sorts the input
bits to ease identification of shareable `$reduce_and` and `$reduce_or`
cells in other passes.
input bits to `$reduce_and` and `$reduce_or` cells. It also sorts the input bits
to ease identification of shareable `$reduce_and` and `$reduce_or` cells in
other passes.
This pass also identifies and consolidates identical inputs to multiplexer
cells. In this case the new shared select bit is driven using a `$reduce_or`
@ -162,8 +162,8 @@ This pass identifies mutually exclusive cells of the same type that:
a. share an input signal, and
b. drive the same `$mux`, `$_MUX_`, or `$pmux` multiplexing cell,
allowing the cell to be merged and the multiplexer to be moved from
multiplexing its output to multiplexing the non-shared input signals.
allowing the cell to be merged and the multiplexer to be moved from multiplexing
its output to multiplexing the non-shared input signals.
.. literalinclude:: /code_examples/opt/opt_share.ys
:language: Verilog
@ -176,16 +176,16 @@ multiplexing its output to multiplexing the non-shared input signals.
Before and after `opt_share`
When running `opt` in full, the original `$mux` (labeled ``$3``) is
optimized away by `opt_expr`.
When running `opt` in full, the original `$mux` (labeled ``$3``) is optimized
away by `opt_expr`.
Performing DFF optimizations - `opt_dff`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This pass identifies single-bit d-type flip-flops (`$_DFF_`, `$dff`, and
`$adff` cells) with a constant data input and replaces them with a constant
driver. It can also merge clock enables and synchronous reset multiplexers,
removing unused control inputs.
This pass identifies single-bit d-type flip-flops (`$_DFF_`, `$dff`, and `$adff`
cells) with a constant data input and replaces them with a constant driver. It
can also merge clock enables and synchronous reset multiplexers, removing unused
control inputs.
Called with ``-nodffe`` and ``-nosdff``, this pass is used to prepare a design
for :doc:`/using_yosys/synthesis/fsm`.
@ -200,20 +200,20 @@ attribute can be used for debugging or by other optimization passes.
When to use `opt` or `clean`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Usually it does not hurt to call `opt` after each regular command in
the synthesis script. But it increases the synthesis time, so it is favourable
to only call `opt` when an improvement can be achieved.
Usually it does not hurt to call `opt` after each regular command in the
synthesis script. But it increases the synthesis time, so it is favourable to
only call `opt` when an improvement can be achieved.
It is generally a good idea to call `opt` before inherently expensive
commands such as `sat` or `freduce`, as the possible gain is
much higher in these cases as the possible loss.
It is generally a good idea to call `opt` before inherently expensive commands
such as `sat` or `freduce`, as the possible gain is much higher in these cases
as the possible loss.
The `clean` command, which is an alias for `opt_clean` with
fewer outputs, on the other hand is very fast and many commands leave a mess
(dangling signal wires, etc). For example, most commands do not remove any wires
or cells. They just change the connections and depend on a later call to clean
to get rid of the now unused objects. So the occasional ``;;``, which itself is
an alias for `clean`, is a good idea in every synthesis script, e.g:
The `clean` command, which is an alias for `opt_clean` with fewer outputs, on
the other hand is very fast and many commands leave a mess (dangling signal
wires, etc). For example, most commands do not remove any wires or cells. They
just change the connections and depend on a later call to clean to get rid of
the now unused objects. So the occasional ``;;``, which itself is an alias for
`clean`, is a good idea in every synthesis script, e.g:
.. code-block:: yoscrypt

18
docs/source/using_yosys/synthesis/proc.rst
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@ -5,23 +5,23 @@ Converting process blocks
:language: yoscrypt
The Verilog frontend converts ``always``-blocks to RTL netlists for the
expressions and "processess" for the control- and memory elements. The
`proc` command then transforms these "processess" to netlists of RTL
multiplexer and register cells. It also is a macro command that calls the other
``proc_*`` commands in a sensible order:
expressions and "processess" for the control- and memory elements. The `proc`
command then transforms these "processess" to netlists of RTL multiplexer and
register cells. It also is a macro command that calls the other ``proc_*``
commands in a sensible order:
.. literalinclude:: /code_examples/macro_commands/proc.ys
:language: yoscrypt
:start-after: #end:
:caption: Passes called by `proc`
After all the ``proc_*`` commands, `opt_expr` is called. This can be
disabled by calling :yoscrypt:`proc -noopt`. For more information about
`proc`, such as disabling certain sub commands, see :doc:`/cmd/proc`.
After all the ``proc_*`` commands, `opt_expr` is called. This can be disabled by
calling :yoscrypt:`proc -noopt`. For more information about `proc`, such as
disabling certain sub commands, see :doc:`/cmd/proc`.
Many commands can not operate on modules with "processess" in them. Usually a
call to `proc` is the first command in the actual synthesis procedure
after design elaboration.
call to `proc` is the first command in the actual synthesis procedure after
design elaboration.
Example
^^^^^^^

15
docs/source/yosys_internals/extending_yosys/extensions.rst
View File

@ -20,8 +20,8 @@ CodingStyle may be of interest.
Quick guide
-----------
Code examples from this section are included in the
|code_examples/extensions|_ directory of the Yosys source code.
Code examples from this section are included in the |code_examples/extensions|_
directory of the Yosys source code.
.. |code_examples/extensions| replace:: :file:`docs/source/code_examples/extensions`
.. _code_examples/extensions: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/extensions
@ -56,10 +56,9 @@ It is possible to only work on this simpler version:
}
When trying to understand what a command does, creating a small test case to
look at the output of `dump` and `show` before and after the
command has been executed can be helpful.
:doc:`/using_yosys/more_scripting/selections` has more information on using
these commands.
look at the output of `dump` and `show` before and after the command has been
executed can be helpful. :doc:`/using_yosys/more_scripting/selections` has more
information on using these commands.
Creating a command
~~~~~~~~~~~~~~~~~~
@ -151,8 +150,8 @@ Most commands modify existing modules, not create new ones.
When modifying existing modules, stick to the following DOs and DON'Ts:
- Do not remove wires. Simply disconnect them and let a successive
`clean` command worry about removing it.
- Do not remove wires. Simply disconnect them and let a successive `clean`
command worry about removing it.
- Use ``module->fixup_ports()`` after changing the ``port_*`` properties of
wires.
- You can safely remove cells or change the ``connections`` property of a cell,

26
docs/source/yosys_internals/flow/verilog_frontend.rst
View File

@ -599,14 +599,14 @@ The proc pass
The ProcessGenerator converts a behavioural model in AST representation to a
behavioural model in ``RTLIL::Process`` representation. The actual conversion
from a behavioural model to an RTL representation is performed by the
`proc` pass and the passes it launches:
from a behavioural model to an RTL representation is performed by the `proc`
pass and the passes it launches:
- | `proc_clean` and `proc_rmdead`
| These two passes just clean up the ``RTLIL::Process`` structure. The
`proc_clean` pass removes empty parts (eg. empty assignments) from
the process and `proc_rmdead` detects and removes unreachable
branches from the process's decision trees.
`proc_clean` pass removes empty parts (eg. empty assignments) from the
process and `proc_rmdead` detects and removes unreachable branches from the
process's decision trees.
- | `proc_arst`
| This pass detects processes that describe d-type flip-flops with
@ -617,10 +617,10 @@ from a behavioural model to an RTL representation is performed by the
and the top-level ``RTLIL::SwitchRule`` has been removed.
- | `proc_mux`
| This pass converts the ``RTLIL::CaseRule``/\ ``RTLIL::SwitchRule``-tree to a
tree of multiplexers per written signal. After this, the ``RTLIL::Process``
structure only contains the ``RTLIL::SyncRule`` s that describe the output
registers.
| This pass converts the ``RTLIL::CaseRule``/\ ``RTLIL::SwitchRule``-tree to
a tree of multiplexers per written signal. After this, the
``RTLIL::Process`` structure only contains the ``RTLIL::SyncRule`` s that
describe the output registers.
- | `proc_dff`
| This pass replaces the ``RTLIL::SyncRule``\ s to d-type flip-flops (with
@ -630,8 +630,8 @@ from a behavioural model to an RTL representation is performed by the
| This pass replaces the ``RTLIL::MemWriteAction``\ s with `$memwr` cells.
- | `proc_clean`
| A final call to `proc_clean` removes the now empty
``RTLIL::Process`` objects.
| A final call to `proc_clean` removes the now empty ``RTLIL::Process``
objects.
Performing these last processing steps in passes instead of in the Verilog
frontend has two important benefits:
@ -646,8 +646,8 @@ to extend the actual Verilog frontend.
.. todo:: Synthesizing Verilog arrays
Add some information on the generation of `$memrd` and `$memwr` cells and
how they are processed in the memory pass.
Add some information on the generation of `$memrd` and `$memwr` cells and how
they are processed in the memory pass.
.. todo:: Synthesizing parametric designs

373
docs/source/yosys_internals/formats/cell_library.rst
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@ -73,16 +73,16 @@ also have the following parameters:
:verilog:`Y = !A` $logic_not
================== ============
For the unary cells that output a logical value (`$reduce_and`,
`$reduce_or`, `$reduce_xor`, `$reduce_xnor`, `$reduce_bool`,
`$logic_not`), when the ``\Y_WIDTH`` parameter is greater than 1, the output
is zero-extended, and only the least significant bit varies.
For the unary cells that output a logical value (`$reduce_and`, `$reduce_or`,
`$reduce_xor`, `$reduce_xnor`, `$reduce_bool`, `$logic_not`), when the
``\Y_WIDTH`` parameter is greater than 1, the output is zero-extended, and only
the least significant bit varies.
Note that `$reduce_or` and `$reduce_bool` actually represent the same logic
function. But the HDL frontends generate them in different situations. A
`$reduce_or` cell is generated when the prefix ``|`` operator is being used. A
`$reduce_bool` cell is generated when a bit vector is used as a condition in
an ``if``-statement or ``?:``-expression.
`$reduce_bool` cell is generated when a bit vector is used as a condition in an
``if``-statement or ``?:``-expression.
Binary operators
~~~~~~~~~~~~~~~~
@ -91,15 +91,15 @@ All binary RTL cells have two input ports ``\A`` and ``\B`` and one output port
``\Y``. They also have the following parameters:
``\A_SIGNED``
Set to a non-zero value if the input ``\A`` is signed and therefore
should be sign-extended when needed.
Set to a non-zero value if the input ``\A`` is signed and therefore should be
sign-extended when needed.
``\A_WIDTH``
The width of the input port ``\A``.
``\B_SIGNED``
Set to a non-zero value if the input ``\B`` is signed and therefore
should be sign-extended when needed.
Set to a non-zero value if the input ``\B`` is signed and therefore should be
sign-extended when needed.
``\B_WIDTH``
The width of the input port ``\B``.
@ -130,29 +130,28 @@ All binary RTL cells have two input ports ``\A`` and ``\B`` and one output port
:verilog:`Y = A ** B` $pow ``N/A`` $modfloor
======================= ============= ======================= =========
The `$shl` and `$shr` cells implement logical shifts, whereas the `$sshl`
and `$sshr` cells implement arithmetic shifts. The `$shl` and `$sshl`
cells implement the same operation. All four of these cells interpret the second
The `$shl` and `$shr` cells implement logical shifts, whereas the `$sshl` and
`$sshr` cells implement arithmetic shifts. The `$shl` and `$sshl` cells
implement the same operation. All four of these cells interpret the second
operand as unsigned, and require ``\B_SIGNED`` to be zero.
Two additional shift operator cells are available that do not directly
correspond to any operator in Verilog, `$shift` and `$shiftx`. The
`$shift` cell performs a right logical shift if the second operand is positive
(or unsigned), and a left logical shift if it is negative. The `$shiftx` cell
performs the same operation as the `$shift` cell, but the vacated bit
positions are filled with undef (x) bits, and corresponds to the Verilog indexed
part-select expression.
correspond to any operator in Verilog, `$shift` and `$shiftx`. The `$shift` cell
performs a right logical shift if the second operand is positive (or unsigned),
and a left logical shift if it is negative. The `$shiftx` cell performs the same
operation as the `$shift` cell, but the vacated bit positions are filled with
undef (x) bits, and corresponds to the Verilog indexed part-select expression.
For the binary cells that output a logical value (`$logic_and`, `$logic_or`,
`$eqx`, `$nex`, `$lt`, `$le`, `$eq`, `$ne`, `$ge`, `$gt`), when
the ``\Y_WIDTH`` parameter is greater than 1, the output is zero-extended, and
only the least significant bit varies.
`$eqx`, `$nex`, `$lt`, `$le`, `$eq`, `$ne`, `$ge`, `$gt`), when the ``\Y_WIDTH``
parameter is greater than 1, the output is zero-extended, and only the least
significant bit varies.
Division and modulo cells are available in two rounding modes. The original
`$div` and `$mod` cells are based on truncating division, and correspond to
the semantics of the verilog ``/`` and ``%`` operators. The `$divfloor` and
`$modfloor` cells represent flooring division and flooring modulo, the latter
of which is also known as "remainder" in several languages. See
`$div` and `$mod` cells are based on truncating division, and correspond to the
semantics of the verilog ``/`` and ``%`` operators. The `$divfloor` and
`$modfloor` cells represent flooring division and flooring modulo, the latter of
which is also known as "remainder" in several languages. See
:numref:`tab:CellLib_divmod` for a side-by-side comparison between the different
semantics.
@ -187,9 +186,9 @@ all of the specified width. This cell also has a single bit control input
it is 1 the value from the ``\B`` input is sent to the output. So the `$mux`
cell implements the function :verilog:`Y = S ? B : A`.
The `$pmux` cell is used to multiplex between many inputs using a one-hot
select signal. Cells of this type have a ``\WIDTH`` and a ``\S_WIDTH`` parameter
and inputs ``\A``, ``\B``, and ``\S`` and an output ``\Y``. The ``\S`` input is
The `$pmux` cell is used to multiplex between many inputs using a one-hot select
signal. Cells of this type have a ``\WIDTH`` and a ``\S_WIDTH`` parameter and
inputs ``\A``, ``\B``, and ``\S`` and an output ``\Y``. The ``\S`` input is
``\S_WIDTH`` bits wide. The ``\A`` input and the output are both ``\WIDTH`` bits
wide and the ``\B`` input is ``\WIDTH*\S_WIDTH`` bits wide. When all bits of
``\S`` are zero, the value from ``\A`` input is sent to the output. If the
@ -199,8 +198,8 @@ from ``\S`` is set the output is undefined. Cells of this type are used to model
"parallel cases" (defined by using the ``parallel_case`` attribute or detected
by an optimization).
The `$tribuf` cell is used to implement tristate logic. Cells of this type
have a ``\WIDTH`` parameter and inputs ``\A`` and ``\EN`` and an output ``\Y``. The
The `$tribuf` cell is used to implement tristate logic. Cells of this type have
a ``\WIDTH`` parameter and inputs ``\A`` and ``\EN`` and an output ``\Y``. The
``\A`` input and ``\Y`` output are ``\WIDTH`` bits wide, and the ``\EN`` input
is one bit wide. When ``\EN`` is 0, the output is not driven. When ``\EN`` is 1,
the value from ``\A`` input is sent to the ``\Y`` output. Therefore, the
@ -224,27 +223,27 @@ parameters:
The width of inputs ``\SET`` and ``\CLR`` and output ``\Q``.
``\SET_POLARITY``
The set input bits are active-high if this parameter has the value
``1'b1`` and active-low if this parameter is ``1'b0``.
The set input bits are active-high if this parameter has the value ``1'b1``
and active-low if this parameter is ``1'b0``.
``\CLR_POLARITY``
The reset input bits are active-high if this parameter has the value
``1'b1`` and active-low if this parameter is ``1'b0``.
The reset input bits are active-high if this parameter has the value ``1'b1``
and active-low if this parameter is ``1'b0``.
Both set and reset inputs have separate bits for every output bit. When both the
set and reset inputs of an `$sr` cell are active for a given bit index, the
reset input takes precedence.
D-type flip-flops are represented by `$dff` cells. These cells have a clock
port ``\CLK``, an input port ``\D`` and an output port ``\Q``. The following
D-type flip-flops are represented by `$dff` cells. These cells have a clock port
``\CLK``, an input port ``\D`` and an output port ``\Q``. The following
parameters are available for `$dff` cells:
``\WIDTH``
The width of input ``\D`` and output ``\Q``.
``\CLK_POLARITY``
Clock is active on the positive edge if this parameter has the value
``1'b1`` and on the negative edge if this parameter is ``1'b0``.
Clock is active on the positive edge if this parameter has the value ``1'b1``
and on the negative edge if this parameter is ``1'b0``.
D-type flip-flops with asynchronous reset are represented by `$adff` cells. As
the `$dff` cells they have ``\CLK``, ``\D`` and ``\Q`` ports. In addition they
@ -258,8 +257,8 @@ additional two parameters:
``\ARST_VALUE``
The state of ``\Q`` will be set to this value when the reset is active.
Usually these cells are generated by the `proc` pass using the
information in the designs RTLIL::Process objects.
Usually these cells are generated by the `proc` pass using the information in
the designs RTLIL::Process objects.
D-type flip-flops with synchronous reset are represented by `$sdff` cells. As
the `$dff` cells they have ``\CLK``, ``\D`` and ``\Q`` ports. In addition they
@ -267,14 +266,14 @@ also have a single-bit ``\SRST`` input port for the reset pin and the following
additional two parameters:
``\SRST_POLARITY``
The synchronous reset is active-high if this parameter has the value
``1'b1`` and active-low if this parameter is ``1'b0``.
The synchronous reset is active-high if this parameter has the value ``1'b1``
and active-low if this parameter is ``1'b0``.
``\SRST_VALUE``
The state of ``\Q`` will be set to this value when the reset is active.
Note that the `$adff` and `$sdff` cells can only be used when the reset
value is constant.
Note that the `$adff` and `$sdff` cells can only be used when the reset value is
constant.
D-type flip-flops with asynchronous load are represented by `$aldff` cells. As
the `$dff` cells they have ``\CLK``, ``\D`` and ``\Q`` ports. In addition they
@ -283,25 +282,24 @@ also have a single-bit ``\ALOAD`` input port for the async load enable pin, a
following additional parameter:
``\ALOAD_POLARITY``
The asynchronous load is active-high if this parameter has the value
``1'b1`` and active-low if this parameter is ``1'b0``.
The asynchronous load is active-high if this parameter has the value ``1'b1``
and active-low if this parameter is ``1'b0``.
D-type flip-flops with asynchronous set and reset are represented by `$dffsr`
cells. As the `$dff` cells they have ``\CLK``, ``\D`` and ``\Q`` ports. In
addition they also have multi-bit ``\SET`` and ``\CLR`` input ports and the
corresponding polarity parameters, like `$sr` cells.
D-type flip-flops with enable are represented by `$dffe`, `$adffe`,
`$aldffe`, `$dffsre`, `$sdffe`, and `$sdffce` cells, which are enhanced
variants of `$dff`, `$adff`, `$aldff`, `$dffsr`, `$sdff` (with reset
over enable) and `$sdff` (with enable over reset) cells, respectively. They
have the same ports and parameters as their base cell. In addition they also
have a single-bit ``\EN`` input port for the enable pin and the following
parameter:
D-type flip-flops with enable are represented by `$dffe`, `$adffe`, `$aldffe`,
`$dffsre`, `$sdffe`, and `$sdffce` cells, which are enhanced variants of `$dff`,
`$adff`, `$aldff`, `$dffsr`, `$sdff` (with reset over enable) and `$sdff` (with
enable over reset) cells, respectively. They have the same ports and parameters
as their base cell. In addition they also have a single-bit ``\EN`` input port
for the enable pin and the following parameter:
``\EN_POLARITY``
The enable input is active-high if this parameter has the value ``1'b1``
and active-low if this parameter is ``1'b0``.
The enable input is active-high if this parameter has the value ``1'b1`` and
active-low if this parameter is ``1'b0``.
D-type latches are represented by `$dlatch` cells. These cells have an enable
port ``\EN``, an input port ``\D``, and an output port ``\Q``. The following
@ -311,14 +309,14 @@ parameters are available for `$dlatch` cells:
The width of input ``\D`` and output ``\Q``.
``\EN_POLARITY``
The enable input is active-high if this parameter has the value ``1'b1``
and active-low if this parameter is ``1'b0``.
The enable input is active-high if this parameter has the value ``1'b1`` and
active-low if this parameter is ``1'b0``.
The latch is transparent when the ``\EN`` input is active.
D-type latches with reset are represented by `$adlatch` cells. In addition to
`$dlatch` ports and parameters, they also have a single-bit ``\ARST`` input
port for the reset pin and the following additional parameters:
`$dlatch` ports and parameters, they also have a single-bit ``\ARST`` input port
for the reset pin and the following additional parameters:
``\ARST_POLARITY``
The asynchronous reset is active-high if this parameter has the value
@ -363,56 +361,53 @@ parameters:
The number of address bits (width of the ``\ADDR`` input port).
``\WIDTH``
The number of data bits (width of the ``\DATA`` output port). Note that
this may be a power-of-two multiple of the underlying memory's width --
such ports are called wide ports and access an aligned group of cells at
once. In this case, the corresponding low bits of ``\ADDR`` must be
tied to 0.
The number of data bits (width of the ``\DATA`` output port). Note that this
may be a power-of-two multiple of the underlying memory's width -- such ports
are called wide ports and access an aligned group of cells at once. In this
case, the corresponding low bits of ``\ADDR`` must be tied to 0.
``\CLK_ENABLE``
When this parameter is non-zero, the clock is used. Otherwise this read
port is asynchronous and the ``\CLK`` input is not used.
When this parameter is non-zero, the clock is used. Otherwise this read port
is asynchronous and the ``\CLK`` input is not used.
``\CLK_POLARITY``
Clock is active on the positive edge if this parameter has the value
``1'b1`` and on the negative edge if this parameter is ``1'b0``.
Clock is active on the positive edge if this parameter has the value ``1'b1``
and on the negative edge if this parameter is ``1'b0``.
``\TRANSPARENCY_MASK``
This parameter is a bitmask of write ports that this read port is
transparent with. The bits of this parameter are indexed by the write
port's ``\PORTID`` parameter. Transparency can only be enabled between
synchronous ports sharing a clock domain. When transparency is enabled
for a given port pair, a read and write to the same address in the same
cycle will return the new value. Otherwise the old value is returned.
This parameter is a bitmask of write ports that this read port is transparent
with. The bits of this parameter are indexed by the write port's ``\PORTID``
parameter. Transparency can only be enabled between synchronous ports sharing
a clock domain. When transparency is enabled for a given port pair, a read
and write to the same address in the same cycle will return the new value.
Otherwise the old value is returned.
``\COLLISION_X_MASK``
This parameter is a bitmask of write ports that have undefined collision
behavior with this port. The bits of this parameter are indexed by the
write port's ``\PORTID`` parameter. This behavior can only be enabled
between synchronous ports sharing a clock domain. When undefined
collision is enabled for a given port pair, a read and write to the same
address in the same cycle will return the undefined (all-X) value.This
option is exclusive (for a given port pair) with the transparency
option.
behavior with this port. The bits of this parameter are indexed by the write
port's ``\PORTID`` parameter. This behavior can only be enabled between
synchronous ports sharing a clock domain. When undefined collision is enabled
for a given port pair, a read and write to the same address in the same cycle
will return the undefined (all-X) value.This option is exclusive (for a given
port pair) with the transparency option.
``\ARST_VALUE``
Whenever the ``\ARST`` input is asserted, the data output will be reset
to this value. Only used for synchronous ports.
Whenever the ``\ARST`` input is asserted, the data output will be reset to
this value. Only used for synchronous ports.
``\SRST_VALUE``
Whenever the ``\SRST`` input is synchronously asserted, the data output
will be reset to this value. Only used for synchronous ports.
Whenever the ``\SRST`` input is synchronously asserted, the data output will
be reset to this value. Only used for synchronous ports.
``\INIT_VALUE``
The initial value of the data output, for synchronous ports.
``\CE_OVER_SRST``
If this parameter is non-zero, the ``\SRST`` input is only recognized
when ``\EN`` is true. Otherwise, ``\SRST`` is recognized regardless of
``\EN``.
If this parameter is non-zero, the ``\SRST`` input is only recognized when
``\EN`` is true. Otherwise, ``\SRST`` is recognized regardless of ``\EN``.
The `$memwr_v2` cells have a clock input ``\CLK``, an enable input ``\EN``
(one enable bit for each data bit), an address input ``\ADDR`` and a data input
The `$memwr_v2` cells have a clock input ``\CLK``, an enable input ``\EN`` (one
enable bit for each data bit), an address input ``\ADDR`` and a data input
``\DATA``. They also have the following parameters:
``\MEMID``
@ -424,16 +419,16 @@ The `$memwr_v2` cells have a clock input ``\CLK``, an enable input ``\EN``
``\WIDTH``
The number of data bits (width of the ``\DATA`` output port). Like with
`$memrd_v2` cells, the width is allowed to be any power-of-two
multiple of memory width, with the corresponding restriction on address.
`$memrd_v2` cells, the width is allowed to be any power-of-two multiple of
memory width, with the corresponding restriction on address.
``\CLK_ENABLE``
When this parameter is non-zero, the clock is used. Otherwise this write
port is asynchronous and the ``\CLK`` input is not used.
When this parameter is non-zero, the clock is used. Otherwise this write port
is asynchronous and the ``\CLK`` input is not used.
``\CLK_POLARITY``
Clock is active on positive edge if this parameter has the value
``1'b1`` and on the negative edge if this parameter is ``1'b0``.
Clock is active on positive edge if this parameter has the value ``1'b1`` and
on the negative edge if this parameter is ``1'b0``.
``\PORTID``
An identifier for this write port, used to index write port bit mask
@ -442,16 +437,16 @@ The `$memwr_v2` cells have a clock input ``\CLK``, an enable input ``\EN``
``\PRIORITY_MASK``
This parameter is a bitmask of write ports that this write port has priority
over in case of writing to the same address. The bits of this parameter are
indexed by the other write port's ``\PORTID`` parameter. Write ports can
only have priority over write ports with lower port ID. When two ports write
to the same address and neither has priority over the other, the result is
indexed by the other write port's ``\PORTID`` parameter. Write ports can only
have priority over write ports with lower port ID. When two ports write to
the same address and neither has priority over the other, the result is
undefined. Priority can only be set between two synchronous ports sharing
the same clock domain.
The `$meminit_v2` cells have an address input ``\ADDR``, a data input
``\DATA``, with the width of the ``\DATA`` port equal to ``\WIDTH`` parameter
times ``\WORDS`` parameter, and a bit enable mask input ``\EN`` with width equal
to ``\WIDTH`` parameter. All three of the inputs must resolve to a constant for
The `$meminit_v2` cells have an address input ``\ADDR``, a data input ``\DATA``,
with the width of the ``\DATA`` port equal to ``\WIDTH`` parameter times
``\WORDS`` parameter, and a bit enable mask input ``\EN`` with width equal to
``\WIDTH`` parameter. All three of the inputs must resolve to a constant for
synthesis to succeed.
``\MEMID``
@ -472,19 +467,18 @@ synthesis to succeed.
initialization conflict.
The HDL frontend models a memory using ``RTLIL::Memory`` objects and
asynchronous `$memrd_v2` and `$memwr_v2` cells. The `memory` pass
(i.e. its various sub-passes) migrates `$dff` cells into the `$memrd_v2` and
`$memwr_v2` cells making them synchronous, then converts them to a single
`$mem_v2` cell and (optionally) maps this cell type to `$dff` cells for the
individual words and multiplexer-based address decoders for the read and write
interfaces. When the last step is disabled or not possible, a `$mem_v2` cell
is left in the design.
asynchronous `$memrd_v2` and `$memwr_v2` cells. The `memory` pass (i.e. its
various sub-passes) migrates `$dff` cells into the `$memrd_v2` and `$memwr_v2`
cells making them synchronous, then converts them to a single `$mem_v2` cell and
(optionally) maps this cell type to `$dff` cells for the individual words and
multiplexer-based address decoders for the read and write interfaces. When the
last step is disabled or not possible, a `$mem_v2` cell is left in the design.
The `$mem_v2` cell provides the following parameters:
``\MEMID``
The name of the original ``RTLIL::Memory`` object that became this
`$mem_v2` cell.
The name of the original ``RTLIL::Memory`` object that became this `$mem_v2`
cell.
``\SIZE``
The number of words in the memory.
@ -502,19 +496,19 @@ The `$mem_v2` cell provides the following parameters:
The number of read ports on this memory cell.
``\RD_WIDE_CONTINUATION``
This parameter is ``\RD_PORTS`` bits wide, containing a bitmask of
"wide continuation" read ports. Such ports are used to represent the
extra data bits of wide ports in the combined cell, and must have all
control signals identical with the preceding port, except for address,
which must have the proper sub-cell address encoded in the low bits.
This parameter is ``\RD_PORTS`` bits wide, containing a bitmask of "wide
continuation" read ports. Such ports are used to represent the extra data
bits of wide ports in the combined cell, and must have all control signals
identical with the preceding port, except for address, which must have the
proper sub-cell address encoded in the low bits.
``\RD_CLK_ENABLE``
This parameter is ``\RD_PORTS`` bits wide, containing a clock enable bit
for each read port.
This parameter is ``\RD_PORTS`` bits wide, containing a clock enable bit for
each read port.
``\RD_CLK_POLARITY``
This parameter is ``\RD_PORTS`` bits wide, containing a clock polarity
bit for each read port.
This parameter is ``\RD_PORTS`` bits wide, containing a clock polarity bit
for each read port.
``\RD_TRANSPARENCY_MASK``
This parameter is ``\RD_PORTS*\WR_PORTS`` bits wide, containing a
@ -523,62 +517,62 @@ The `$mem_v2` cell provides the following parameters:
``\RD_COLLISION_X_MASK``
This parameter is ``\RD_PORTS*\WR_PORTS`` bits wide, containing a
concatenation of all ``\COLLISION_X_MASK`` values of the original
`$memrd_v2` cells.
concatenation of all ``\COLLISION_X_MASK`` values of the original `$memrd_v2`
cells.
``\RD_CE_OVER_SRST``
This parameter is ``\RD_PORTS`` bits wide, determining relative
synchronous reset and enable priority for each read port.
This parameter is ``\RD_PORTS`` bits wide, determining relative synchronous
reset and enable priority for each read port.
``\RD_INIT_VALUE``
This parameter is ``\RD_PORTS*\WIDTH`` bits wide, containing the initial
value for each synchronous read port.
``\RD_ARST_VALUE``
This parameter is ``\RD_PORTS*\WIDTH`` bits wide, containing the
asynchronous reset value for each synchronous read port.
This parameter is ``\RD_PORTS*\WIDTH`` bits wide, containing the asynchronous
reset value for each synchronous read port.
``\RD_SRST_VALUE``
This parameter is ``\RD_PORTS*\WIDTH`` bits wide, containing the
synchronous reset value for each synchronous read port.
This parameter is ``\RD_PORTS*\WIDTH`` bits wide, containing the synchronous
reset value for each synchronous read port.
``\WR_PORTS``
The number of write ports on this memory cell.
``\WR_WIDE_CONTINUATION``
This parameter is ``\WR_PORTS`` bits wide, containing a bitmask of
"wide continuation" write ports.
This parameter is ``\WR_PORTS`` bits wide, containing a bitmask of "wide
continuation" write ports.
``\WR_CLK_ENABLE``
This parameter is ``\WR_PORTS`` bits wide, containing a clock enable bit
for each write port.
This parameter is ``\WR_PORTS`` bits wide, containing a clock enable bit for
each write port.
``\WR_CLK_POLARITY``
This parameter is ``\WR_PORTS`` bits wide, containing a clock polarity
bit for each write port.
This parameter is ``\WR_PORTS`` bits wide, containing a clock polarity bit
for each write port.
``\WR_PRIORITY_MASK``
This parameter is ``\WR_PORTS*\WR_PORTS`` bits wide, containing a
concatenation of all ``\PRIORITY_MASK`` values of the original
`$memwr_v2` cells.
concatenation of all ``\PRIORITY_MASK`` values of the original `$memwr_v2`
cells.
The `$mem_v2` cell has the following ports:
``\RD_CLK``
This input is ``\RD_PORTS`` bits wide, containing all clock signals for
the read ports.
This input is ``\RD_PORTS`` bits wide, containing all clock signals for the
read ports.
``\RD_EN``
This input is ``\RD_PORTS`` bits wide, containing all enable signals for
the read ports.
This input is ``\RD_PORTS`` bits wide, containing all enable signals for the
read ports.
``\RD_ADDR``
This input is ``\RD_PORTS*\ABITS`` bits wide, containing all address
signals for the read ports.
This input is ``\RD_PORTS*\ABITS`` bits wide, containing all address signals
for the read ports.
``\RD_DATA``
This output is ``\RD_PORTS*\WIDTH`` bits wide, containing all data
signals for the read ports.
This output is ``\RD_PORTS*\WIDTH`` bits wide, containing all data signals
for the read ports.
``\RD_ARST``
This input is ``\RD_PORTS`` bits wide, containing all asynchronous reset
@ -593,26 +587,25 @@ The `$mem_v2` cell has the following ports:
the write ports.
``\WR_EN``
This input is ``\WR_PORTS*\WIDTH`` bits wide, containing all enable
signals for the write ports.
This input is ``\WR_PORTS*\WIDTH`` bits wide, containing all enable signals
for the write ports.
``\WR_ADDR``
This input is ``\WR_PORTS*\ABITS`` bits wide, containing all address
signals for the write ports.
This input is ``\WR_PORTS*\ABITS`` bits wide, containing all address signals
for the write ports.
``\WR_DATA``
This input is ``\WR_PORTS*\WIDTH`` bits wide, containing all data
signals for the write ports.
This input is ``\WR_PORTS*\WIDTH`` bits wide, containing all data signals for
the write ports.
The `memory_collect` pass can be used to convert discrete
`$memrd_v2`, `$memwr_v2`, and `$meminit_v2` cells belonging to the same
memory to a single `$mem_v2` cell, whereas the `memory_unpack` pass
performs the inverse operation. The `memory_dff` pass can combine
asynchronous memory ports that are fed by or feeding registers into synchronous
memory ports. The `memory_bram` pass can be used to recognize
`$mem_v2` cells that can be implemented with a block RAM resource on an FPGA.
The `memory_map` pass can be used to implement `$mem_v2` cells as
basic logic: word-wide DFFs and address decoders.
The `memory_collect` pass can be used to convert discrete `$memrd_v2`,
`$memwr_v2`, and `$meminit_v2` cells belonging to the same memory to a single
`$mem_v2` cell, whereas the `memory_unpack` pass performs the inverse operation.
The `memory_dff` pass can combine asynchronous memory ports that are fed by or
feeding registers into synchronous memory ports. The `memory_bram` pass can be
used to recognize `$mem_v2` cells that can be implemented with a block RAM
resource on an FPGA. The `memory_map` pass can be used to implement `$mem_v2`
cells as basic logic: word-wide DFFs and address decoders.
Finite state machines
~~~~~~~~~~~~~~~~~~~~~
@ -622,15 +615,17 @@ Add a brief description of the `$fsm` cell type.
Coarse arithmetics
~~~~~~~~~~~~~~~~~~~~~
The `$macc` cell type represents a generalized multiply and accumulate operation. The cell is purely combinational. It outputs the result of summing up a sequence of products and other injected summands.
The `$macc` cell type represents a generalized multiply and accumulate
operation. The cell is purely combinational. It outputs the result of summing up
a sequence of products and other injected summands.
.. code-block::
Y = 0 +- a0factor1 * a0factor2 +- a1factor1 * a1factor2 +- ...
+ B[0] + B[1] + ...
The A port consists of concatenated pairs of multiplier inputs ("factors").
A zero length factor2 acts as a constant 1, turning factor1 into a simple summand.
The A port consists of concatenated pairs of multiplier inputs ("factors"). A
zero length factor2 acts as a constant 1, turning factor1 into a simple summand.
In this pseudocode, ``u(foo)`` means an unsigned int that's foo bits long.
@ -644,8 +639,8 @@ In this pseudocode, ``u(foo)`` means an unsigned int that's foo bits long.
...
};
The cell's ``CONFIG`` parameter determines the layout of cell port ``A``.
The CONFIG parameter carries the following information:
The cell's ``CONFIG`` parameter determines the layout of cell port ``A``. The
CONFIG parameter carries the following information:
.. code-block::
@ -714,8 +709,8 @@ Formal verification cells
~~~~~~~~~~~~~~~~~~~~~~~~~
Add information about `$check`, `$assert`, `$assume`, `$live`, `$fair`,
`$cover`, `$equiv`, `$initstate`, `$anyconst`, `$anyseq`,
`$anyinit`, `$allconst`, `$allseq` cells.
`$cover`, `$equiv`, `$initstate`, `$anyconst`, `$anyseq`, `$anyinit`,
`$allconst`, `$allseq` cells.
Add information about `$ff` and `$_FF_` cells.
@ -733,8 +728,8 @@ has the following parameters:
The width (in bits) of the signal on the ``\ARGS`` port.
``\TRG_ENABLE``
True if triggered on specific signals defined in ``\TRG``; false if
triggered whenever ``\ARGS`` or ``\EN`` change and ``\EN`` is 1.
True if triggered on specific signals defined in ``\TRG``; false if triggered
whenever ``\ARGS`` or ``\EN`` change and ``\EN`` is 1.
If ``\TRG_ENABLE`` is true, the following parameters also apply:
@ -792,12 +787,13 @@ width\ *?*
(optional) The number of characters wide to pad to.
base
* ``b`` for base-2 integers (binary)
* ``o`` for base-8 integers (octal)
* ``d`` for base-10 integers (decimal)
* ``h`` for base-16 integers (hexadecimal)
* ``c`` for ASCII characters/strings
* ``t`` and ``r`` for simulation time (corresponding to :verilog:`$time` and :verilog:`$realtime`)
* ``b`` for base-2 integers (binary)
* ``o`` for base-8 integers (octal)
* ``d`` for base-10 integers (decimal)
* ``h`` for base-16 integers (hexadecimal)
* ``c`` for ASCII characters/strings
* ``t`` and ``r`` for simulation time (corresponding to :verilog:`$time` and
:verilog:`$realtime`)
For integers, this item may follow:
@ -1042,14 +1038,13 @@ Tables :numref:`%s <tab:CellLib_gates>`, :numref:`%s <tab:CellLib_gates_dffe>`,
:numref:`%s <tab:CellLib_gates_adlatch>`, :numref:`%s
<tab:CellLib_gates_dlatchsr>` and :numref:`%s <tab:CellLib_gates_sr>` list all
cell types used for gate level logic. The cell types `$_BUF_`, `$_NOT_`,
`$_AND_`, `$_NAND_`, `$_ANDNOT_`, `$_OR_`, `$_NOR_`, `$_ORNOT_`,
`$_XOR_`, `$_XNOR_`, `$_AOI3_`, `$_OAI3_`, `$_AOI4_`, `$_OAI4_`,
`$_MUX_`, `$_MUX4_`, `$_MUX8_`, `$_MUX16_` and `$_NMUX_` are used to
model combinatorial logic. The cell type `$_TBUF_` is used to model tristate
logic.
`$_AND_`, `$_NAND_`, `$_ANDNOT_`, `$_OR_`, `$_NOR_`, `$_ORNOT_`, `$_XOR_`,
`$_XNOR_`, `$_AOI3_`, `$_OAI3_`, `$_AOI4_`, `$_OAI4_`, `$_MUX_`, `$_MUX4_`,
`$_MUX8_`, `$_MUX16_` and `$_NMUX_` are used to model combinatorial logic. The
cell type `$_TBUF_` is used to model tristate logic.
The `$_MUX4_`, `$_MUX8_` and `$_MUX16_` cells are used to model wide
muxes, and correspond to the following Verilog code:
The `$_MUX4_`, `$_MUX8_` and `$_MUX16_` cells are used to model wide muxes, and
correspond to the following Verilog code:
.. code-block:: verilog
:force:
@ -1114,8 +1109,8 @@ following Verilog code template:
The cell types ``$_DFFE_[NP][NP][01][NP]_`` implement d-type flip-flops with
asynchronous reset and enable. The values in the table for these cell types
relate to the following Verilog code template, where ``RST_EDGE`` is
``posedge`` if ``RST_LVL`` if ``1``, and ``negedge`` otherwise.
relate to the following Verilog code template, where ``RST_EDGE`` is ``posedge``
if ``RST_LVL`` if ``1``, and ``negedge`` otherwise.
.. code-block:: verilog
:force:
@ -1156,8 +1151,8 @@ in the table for these cell types relate to the following Verilog code template:
The cell types ``$_DFFSR_[NP][NP][NP]_`` implement d-type flip-flops with
asynchronous set and reset. The values in the table for these cell types relate
to the following Verilog code template, where ``RST_EDGE`` is ``posedge`` if
``RST_LVL`` if ``1``, ``negedge`` otherwise, and ``SET_EDGE`` is ``posedge``
if ``SET_LVL`` if ``1``, ``negedge`` otherwise.
``RST_LVL`` if ``1``, ``negedge`` otherwise, and ``SET_EDGE`` is ``posedge`` if
``SET_LVL`` if ``1``, ``negedge`` otherwise.
.. code-block:: verilog
:force:
@ -1173,8 +1168,8 @@ if ``SET_LVL`` if ``1``, ``negedge`` otherwise.
The cell types ``$_DFFSRE_[NP][NP][NP][NP]_`` implement d-type flip-flops with
asynchronous set and reset and enable. The values in the table for these cell
types relate to the following Verilog code template, where ``RST_EDGE`` is
``posedge`` if ``RST_LVL`` if ``1``, ``negedge`` otherwise, and ``SET_EDGE``
is ``posedge`` if ``SET_LVL`` if ``1``, ``negedge`` otherwise.
``posedge`` if ``RST_LVL`` if ``1``, ``negedge`` otherwise, and ``SET_EDGE`` is
``posedge`` if ``SET_LVL`` if ``1``, ``negedge`` otherwise.
.. code-block:: verilog
:force:

47
docs/source/yosys_internals/formats/rtlil_rep.rst
View File

@ -76,11 +76,10 @@ This has three advantages:
- Second, the information about which identifiers were originally provided by
the user is always available which can help guide some optimizations. For
example, `opt_clean` tries to preserve signals with a user-provided
name but doesn't hesitate to delete signals that have auto-generated names
when they just duplicate other signals. Note that this can be overridden
with the ``-purge`` option to also delete internal nets with user-provided
names.
example, `opt_clean` tries to preserve signals with a user-provided name but
doesn't hesitate to delete signals that have auto-generated names when they
just duplicate other signals. Note that this can be overridden with the
``-purge`` option to also delete internal nets with user-provided names.
- Third, the delicate job of finding suitable auto-generated public visible
names is deferred to one central location. Internally auto-generated names
@ -204,8 +203,8 @@ A "signal" is everything that can be applied to a cell port. I.e.
- | Concatenations of the above
| 1em For example: ``{16'd1337, mywire[15:8]}``
The ``RTLIL::SigSpec`` data type is used to represent signals. The ``RTLIL::Cell``
object contains one ``RTLIL::SigSpec`` for each cell port.
The ``RTLIL::SigSpec`` data type is used to represent signals. The
``RTLIL::Cell`` object contains one ``RTLIL::SigSpec`` for each cell port.
In addition, connections between wires are represented using a pair of
``RTLIL::SigSpec`` objects. Such pairs are needed in different locations.
@ -234,9 +233,9 @@ control logic of the behavioural code. Let's consider a simple example:
q <= d;
endmodule
In this example there is no data path and therefore the ``RTLIL::Module`` generated
by the frontend only contains a few ``RTLIL::Wire`` objects and an ``RTLIL::Process`` .
The ``RTLIL::Process`` in RTLIL syntax:
In this example there is no data path and therefore the ``RTLIL::Module``
generated by the frontend only contains a few ``RTLIL::Wire`` objects and an
``RTLIL::Process``. The ``RTLIL::Process`` in RTLIL syntax:
.. code:: RTLIL
:number-lines:
@ -320,8 +319,8 @@ trees before further processing them.
One of the first actions performed on a design in RTLIL representation in most
synthesis scripts is identifying asynchronous resets. This is usually done using
the `proc_arst` pass. This pass transforms the above example to the
following ``RTLIL::Process``:
the `proc_arst` pass. This pass transforms the above example to the following
``RTLIL::Process``:
.. code:: RTLIL
:number-lines:
@ -340,9 +339,9 @@ following ``RTLIL::Process``:
end
This pass has transformed the outer ``RTLIL::SwitchRule`` into a modified
``RTLIL::SyncRule`` object for the ``\reset`` signal. Further processing converts the
``RTLIL::Process`` into e.g. a d-type flip-flop with asynchronous reset and a
multiplexer for the enable signal:
``RTLIL::SyncRule`` object for the ``\reset`` signal. Further processing
converts the ``RTLIL::Process`` into e.g. a d-type flip-flop with asynchronous
reset and a multiplexer for the enable signal:
.. code:: RTLIL
:number-lines:
@ -365,11 +364,11 @@ multiplexer for the enable signal:
connect \Y $0\q[0:0]
end
Different combinations of passes may yield different results. Note that
`$adff` and `$mux` are internal cell types that still need to be mapped to
cell types from the target cell library.
Different combinations of passes may yield different results. Note that `$adff`
and `$mux` are internal cell types that still need to be mapped to cell types
from the target cell library.
Some passes refuse to operate on modules that still contain ``RTLIL::Process``
Some passes refuse to operate on modules that still contain ``RTLIL::Process``
objects as the presence of these objects in a module increases the complexity.
Therefore the passes to translate processes to a netlist of cells are usually
called early in a synthesis script. The proc pass calls a series of other passes
@ -389,9 +388,9 @@ A memory object has the following properties:
- The width of an addressable word
- The size of the memory in number of words
All read accesses to the memory are transformed to `$memrd` cells and all
write accesses to `$memwr` cells by the language frontend. These cells consist
of independent read- and write-ports to the memory. Memory initialization is
All read accesses to the memory are transformed to `$memrd` cells and all write
accesses to `$memwr` cells by the language frontend. These cells consist of
independent read- and write-ports to the memory. Memory initialization is
transformed to `$meminit` cells by the language frontend. The ``\MEMID``
parameter on these cells is used to link them together and to the
``RTLIL::Memory`` object they belong to.
@ -402,8 +401,8 @@ the separate `$memrd` and `$memwr` cells can be consolidated using resource
sharing. As resource sharing is a non-trivial optimization problem where
different synthesis tasks can have different requirements it lends itself to do
the optimisation in separate passes and merge the ``RTLIL::Memory`` objects and
`$memrd` and `$memwr` cells to multiport memory blocks after resource
sharing is completed.
`$memrd` and `$memwr` cells to multiport memory blocks after resource sharing is
completed.
The memory pass performs this conversion and can (depending on the options
passed to it) transform the memories directly to d-type flip-flops and address

8
docs/source/yosys_internals/techmap.rst
View File

@ -1,8 +1,8 @@
Techmap by example
------------------
As a quick recap, the `techmap` command replaces cells in the design
with implementations given as Verilog code (called "map files"). It can replace
As a quick recap, the `techmap` command replaces cells in the design with
implementations given as Verilog code (called "map files"). It can replace
Yosys' internal cell types (such as `$or`) as well as user-defined cell types.
- Verilog parameters are used extensively to customize the internal cell types.
@ -94,8 +94,8 @@ Scripting in map modules
.. note:: PROTIP:
Commands such as `shell`, ``show -pause``, and `dump` can
be used in the ``_TECHMAP_DO_*`` scripts for debugging map modules.
Commands such as `shell`, ``show -pause``, and `dump` can be used in the
``_TECHMAP_DO_*`` scripts for debugging map modules.
Example: