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Converting a number of inline commands to refs 

Also reflowing text for line width.
Maybe look into supporting commands with options?
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docs/source/appendix/APPNOTE_010_Verilog_to_BLIF.rst
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@ -235,8 +235,8 @@ signal is connected throughout the whole design hierarchy.
endmodule
In line 18 the ``proc`` command is called. But in this script the signal name
globrst is passed to the command as a global reset signal for resetting the
In line 18 the :cmd:ref:`proc` command is called. But in this script the signal
name globrst is passed to the command as a global reset signal for resetting the
registers to their assigned initial values.
Finally in line 19 the techmap command is used to replace all instances of

293
docs/source/appendix/APPNOTE_011_Design_Investigation.rst
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@ -6,9 +6,9 @@ Installation and prerequisites
==============================
This Application Note is based on the `Yosys GIT`_ `Rev. 2b90ba1`_ from
2013-12-08. The README file covers how to install Yosys. The ``show`` command
requires a working installation of `GraphViz`_ and `xdot` for generating the
actual circuit diagrams.
2013-12-08. The README file covers how to install Yosys. The :cmd:ref:`show`
command requires a working installation of `GraphViz`_ and `xdot` for generating
the actual circuit diagrams.
.. _Yosys GIT: https://github.com/YosysHQ/yosys
@ -23,8 +23,8 @@ Overview
This application note is structured as follows:
:ref:`intro_show` introduces the ``show`` command and explains the symbols used
in the circuit diagrams generated by it.
:ref:`intro_show` introduces the :cmd:ref:`show` command and explains the
symbols used in the circuit diagrams generated by it.
:ref:`navigate` introduces additional commands used to navigate in the design,
select portions of the design, and print additional information on the elements
@ -41,7 +41,7 @@ Introduction to the show command
================================
.. code-block:: console
:caption: Yosys script with ``show`` commands and example design
:caption: Yosys script with :cmd:ref:`show` commands and example design
:name: example_src
$ cat example.ys
@ -64,24 +64,24 @@ Introduction to the show command
:class: width-helper
:name: example_out
Output of the three ``show`` commands from :numref:`example_src`
Output of the three :cmd:ref:`show` commands from :numref:`example_src`
The ``show`` command generates a circuit diagram for the design in its current
state. Various options can be used to change the appearance of the circuit
diagram, set the name and format for the output file, and so forth. When called
without any special options, it saves the circuit diagram in a temporary file
and launches ``xdot`` to display the diagram. Subsequent calls to show re-use the
``xdot`` instance (if still running).
The :cmd:ref:`show` command generates a circuit diagram for the design in its
current state. Various options can be used to change the appearance of the
circuit diagram, set the name and format for the output file, and so forth. When
called without any special options, it saves the circuit diagram in a temporary
file and launches ``xdot`` to display the diagram. Subsequent calls to show
re-use the ``xdot`` instance (if still running).
A simple circuit
----------------
:numref:`example_src` shows a simple synthesis script and a Verilog file that
demonstrate the usage of show in a simple setting. Note that ``show`` is called with
the ``-pause`` option, that halts execution of the Yosys script until the user
presses the Enter key. The ``show -pause`` command also allows the user to enter
an interactive shell to further investigate the circuit before continuing
synthesis.
demonstrate the usage of show in a simple setting. Note that :cmd:ref:`show` is
called with the :cmd:ref:`-pause` option, that halts execution of the Yosys
script until the user presses the Enter key. The ``show -pause`` command also
allows the user to enter an interactive shell to further investigate the circuit
before continuing synthesis.
So this script, when executed, will show the design after each of the three
synthesis commands. The generated circuit diagrams are shown in
@ -111,28 +111,28 @@ original ``always``-block in the 2nd line. Note how the multiplexer from the
``?:``-expression is represented as a ``$mux`` cell but the multiplexer from the
``if``-statement is yet still hidden within the process.
The ``proc`` command transforms the process from the first diagram into a
The :cmd:ref:`proc` command transforms the process from the first diagram into a
multiplexer and a d-type flip-flip, which brings us to the 2nd 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. This 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
``BUF``-node. This are artefacts left behind by the :cmd:ref:`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 this 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``.
:cmd:ref:`clean` (or :cmd:ref:`proc`, which includes :cmd:ref:`clean` as one of
its operations) will clean up this 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 :cmd:ref:`clean` before calling :cmd:ref:`show`.
In this script we directly call ``opt`` as next step, which finally leads us to
the 3rd diagram in :numref:`example_out`. 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.
In this script we directly call :cmd:ref:`proc` as next step, which finally
leads us to the 3rd diagram in :numref:`example_out`. Here we see that the
:cmd:ref:`proc` command not only has removed the artifacts left behind by
:cmd:ref:`proc`, but also determined correctly that it can remove the first
``$mux`` cell without changing the behavior of the circuit.
.. figure:: ../../images/011/splice.*
:class: width-helper
@ -148,7 +148,7 @@ behavior of the circuit.
:class: width-helper
:name: splitnets_libfile
Effects of ``splitnets`` command and of providing a cell library. (The
Effects of :cmd:ref:`splitnets` command and of providing a cell library. (The
circuit is a half-adder built from simple CMOS gates.)
Break-out boxes for signal vectors
@ -158,8 +158,8 @@ As has been indicated by the last example, Yosys is can manage signal vectors
(aka. multi-bit wires or buses) as native objects. This provides great
advantages when analyzing circuits that operate on wide integers. But it also
introduces some additional complexity when the individual bits of of a signal
vector are accessed. The example ``show`` in :numref:`splice_src` demonstrates
how such circuits are visualized by the ``show`` command.
vector are accessed. The example :cmd:ref:`show` in :numref:`splice_src`
demonstrates how such circuits are visualized by the :cmd:ref:`show` command.
The key elements in understanding this circuit diagram are of course the boxes
with round corners and rows labeled ``<MSB_LEFT>:<LSB_LEFT> -
@ -191,11 +191,11 @@ bits, resulting in an unnecessary complex diagram.
For the 2nd diagram 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 :cmd:ref:`show` command using the ``-lib <filename>``
option. Secondly it is possible to load cell libraries into the design with the
``read_verilog -lib <filename>`` command. The 2nd 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.
subsequent calls to the :cmd:ref:`show` command.
In addition to that, the 2nd diagram was generated after ``splitnet -ports`` was
run on the design. This command splits all signal vectors into individual signal
@ -206,21 +206,21 @@ 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.
Per default the :cmd:ref:`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.
In densely connected circuits it is sometimes hard to keep track of the
individual signal wires. For this 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.
individual signal wires. For this cases it can be useful to call :cmd:ref:`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 ``help show`` prints a complete listing of all options supported by
the ``show`` command.
the :cmd:ref:`show` command.
.. _navigate:
@ -232,13 +232,13 @@ only helps in simple cases. For complex modules the generated circuit
diagrams are just stupidly big and are no help at all. In such cases one
first has to select the 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``.
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
:cmd:ref:`techmap` command already fails to verify, it is better to troubleshoot
the coarse-grain version of the circuit before :cmd:ref:`techmap` than the
gate-level circuit after :cmd:ref:`techmap`.
.. Note:: It is generally recommended to verify the internal state of a
design by writing it to a Verilog file using ``write_verilog -noexpr``
@ -249,7 +249,7 @@ Interactive navigation
----------------------
.. code-block:: none
:caption: Demonstration of ``ls`` and ``cd`` using ``example.v`` from :numref:`example_src`
:caption: Demonstration of :cmd:ref:`ls` and :cmd:ref:`cd` using ``example.v`` from :numref:`example_src`
:name: lscd
yosys> ls
@ -293,17 +293,17 @@ Interactive navigation
end
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 :cmd:ref:`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. :numref:`lscd` demonstrates this
using the design from :numref:`example_src`.
the synthesis script does not already narrow the selection). The command
:cmd:ref:`ls` can now be used to create a list of all modules. The command
:cmd:ref:`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.
:numref:`lscd` demonstrates this using the design from :numref:`example_src`.
There is a thing to note in :numref:`lscd`: We can see that the cell names from
:numref:`example_out` are just abbreviations of the actual cell names, namely
@ -312,16 +312,16 @@ 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
:cmd:ref:`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 ``dump $2`` will print :numref:`dump2`. This can for example be useful
to determine the names of nets connected to cells, as the net-names are usually
suppressed in the circuit diagram if they are auto-generated.
The :cmd:ref:`dump` command can be used to print all information about an
object. For example ``dump $2`` will print :numref:`dump2`. This can for example
be useful to determine the names of nets connected to cells, as the net-names
are usually suppressed in the circuit diagram if they are auto-generated.
For the remainder of this document we will assume that the commands are
run from module-context and not design-context.
@ -333,23 +333,24 @@ Working with selections
:class: width-helper
:name: seladd
Output of ``show`` after ``select $2`` or ``select t:$add`` (see also
Output of :cmd:ref:`show` after ``select $2`` or ``select t:$add`` (see also
:numref:`example_out`)
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 :cmd:ref:`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.
But for most interactive work we want to further narrow the set of
selected objects. This can be done using the ``select`` command.
But for most interactive work we want to further narrow the set of selected
objects. This can be done using the :cmd:ref:`select` command.
For example, if the command ``select $2`` is executed, a subsequent ``show``
command will yield the diagram shown in :numref:`seladd`. Note that the nets are
now displayed in ellipses. This indicates that they are not selected, but only
shown because the diagram contains a cell that is connected to the net. This of
course makes no difference for the circuit that is shown, but it can be a useful
information when manipulating selections.
For example, if the command ``select $2`` is executed, a subsequent
:cmd:ref:`show` command will yield the diagram shown in :numref:`seladd`. Note
that the nets are now displayed in ellipses. This indicates that they are not
selected, but only shown because the diagram contains a cell that is connected
to the net. This of course makes no difference for the circuit that is shown,
but it can be a useful information when manipulating selections.
Objects can not only be selected by their name but also by other properties. For
example ``select t:$add`` will select all cells of type ``$add``. In this case
@ -366,13 +367,13 @@ matching different properties.
Many commands can operate on explicit selections. For example the command ``dump
t:$add`` will print information on all ``$add`` cells in the active module.
Whenever a command has ``[selection]`` as last argument in its usage help, this
means that it will use the engine behind the ``select`` command to evaluate
additional arguments and use the resulting selection instead of the selection
created by the last ``select`` command.
means that it will use the engine behind the :cmd:ref:`select` command to
evaluate additional arguments and use the resulting selection instead of the
selection created by the last :cmd:ref:`select` command.
Normally the ``select`` command overwrites a previous selection. The commands
``select -add`` and ``select -del`` can be used to add or remove objects from
the current selection.
Normally the :cmd:ref:`select` command overwrites a previous selection. The
commands ``select -add`` and ``select -del`` can be used to add or remove
objects from the current selection.
The command ``select -clear`` can be used to reset the selection to the default,
which is a complete selection of everything in the current module.
@ -391,9 +392,9 @@ Operations on selections
Output of ``show a:sumstuff`` on :numref:`sumprod`
The ``select`` command is actually much more powerful than it might seem on the
first glimpse. When it is called with multiple arguments, each argument is
evaluated and pushed separately on a stack. After all arguments have been
The :cmd:ref:`select` command is actually much more powerful than it might seem
on the first glimpse. When it is called with multiple arguments, each argument
is evaluated and pushed separately on a stack. After all arguments have been
processed it simply creates the union of all elements on the stack. So the
following command will select all ``$add`` cells and all objects with the
``foo`` attribute set:
@ -445,7 +446,7 @@ Selecting logic cones
:numref:`sumprod_01` shows what is called the ``input cone`` of ``sum``, i.e.
all cells and signals that are used to generate the signal ``sum``. The ``%ci``
action can be used to select the input cones of all object in the top selection
in the stack maintained by the ``select`` command.
in the stack maintained by the :cmd:ref:`select` command.
As the ``%x`` action, this commands broadens the selection by one "step".
But this time the operation only works against the direction of data
@ -484,8 +485,8 @@ appended to the ``%ci`` action.
Lets consider the design from :numref:`memdemo_src`. It serves no purpose other
than being a non-trivial circuit for demonstrating some of the advanced Yosys
features. We synthesize the circuit using ``proc; opt; memory; opt`` and change
to the ``memdemo`` module with ``cd memdemo``. If we type ``show`` now we see
the diagram shown in :numref:`memdemo_00`.
to the ``memdemo`` module with ``cd memdemo``. If we type :cmd:ref:`show` now we
see the diagram shown in :numref:`memdemo_00`.
.. literalinclude:: ../APPNOTE_011_Design_Investigation/memdemo.v
:caption: Demo circuit for demonstrating some advanced Yosys features
@ -580,7 +581,7 @@ 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
the :cmd:ref:`select` command. So for example
.. code-block:: yoscrypt
@ -593,9 +594,9 @@ 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 :cmd:ref:`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.
.. _poke:
@ -610,10 +611,10 @@ of the module and wants to carefully read all the debug output created by the
commands in order to spot a problem. This kind of troubleshooting is much easier
if the circuit under investigation is encapsulated in a separate module.
:numref:`submod` shows how the ``submod`` command can be used to split the
circuit from :numref:`memdemo_src` and :numref:`memdemo_00` into its components.
The ``-name`` option is used to specify the name of the new module and also the
name of the new cell in the current module.
:numref:`submod` shows how the :cmd:ref:`submod` command can be used to split
the circuit from :numref:`memdemo_src` and :numref:`memdemo_00` into its
components. The ``-name`` option is used to specify the name of the new module
and also the name of the new cell in the current module.
.. figure:: ../../images/011/submod_dots.*
:class: width-helper
@ -621,7 +622,7 @@ name of the new cell in the current module.
.. code-block:: yoscrypt
:caption: The circuit from :numref:`memdemo_src` and :numref:`memdemo_00`
broken up using ``submod``
broken up using :cmd:ref:`submod`
:name: submod
select -set outstage y %ci2:+$dff[Q,D] %ci*:-$mux[S]:-$dff
@ -634,8 +635,8 @@ name of the new cell in the current module.
Evaluation of combinatorial circuits
------------------------------------
The ``eval`` command can be used to evaluate combinatorial circuits. For example
(see :numref:`submod` for the circuit diagram of ``selstage``):
The :cmd:ref:`eval` command can be used to evaluate combinatorial circuits. For
example (see :numref:`submod` for the circuit diagram of ``selstage``):
::
@ -676,11 +677,11 @@ 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 this
commands can be applied.
Note that the :cmd:ref:`eval` command (as well as the :cmd:ref:`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
:cmd:ref:`flatten` command must be used on modules that instantiate other
modules before this commands can be applied.
Solving combinatorial SAT problems
----------------------------------
@ -754,18 +755,18 @@ 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 :cmd:ref:`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 :cmd:ref:`sat` command that uses a
`SAT`_ solver, `MiniSAT`_, to solve this kind of problems.
.. _SAT: http://en.wikipedia.org/wiki/Circuit_satisfiability
.. _MiniSAT: http://minisat.se/
The ``sat`` command works very similar to the ``eval`` command. The main
The :cmd:ref:`sat` command works very similar to the :cmd:ref:`eval` command. The main
difference is that it is now also possible to set output values and find the
corresponding input values. For Example:
@ -792,8 +793,8 @@ 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 :cmd:ref:`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
@ -812,8 +813,8 @@ 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 in
the second command in :numref:`primesat` (line 31).
the upper 8 bits of ``a`` and ``b`` to zero for the :cmd:ref:`sat` call, as is
done in the second command in :numref:`primesat` (line 31).
The ``-prove`` option used in this example works similar to ``-set``, but tries
to find a case in which the two arguments are not equal. If such a case is not
@ -917,18 +918,18 @@ to this question, as produced by the following 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
The ``-seq 6`` option instructs the :cmd:ref:`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 :cmd:ref:`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 :cmd:ref:`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.
@ -938,27 +939,27 @@ 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 :cmd:ref:`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.
.. _conclusion:
Conclusion
==========
Yosys provides a wide range of functions to analyze and investigate
designs. For many cases it is sufficient to simply display circuit
diagrams, maybe use some additional commands to narrow the scope of the
circuit diagrams to the interesting parts of the circuit. But some cases
require more than that. For this applications Yosys provides commands
that can be used to further inspect the behavior of the circuit, either
by evaluating which output values are generated from certain input
values (``eval``) or by evaluation which input values and initial conditions
can result in a certain behavior at the outputs (``sat``). The SAT command
can even be used to prove (or disprove) theorems regarding the circuit,
in more advanced cases with the additional help of a miter circuit.
Yosys provides a wide range of functions to analyze and investigate designs. For
many cases it is sufficient to simply display circuit diagrams, maybe use some
additional commands to narrow the scope of the circuit diagrams to the
interesting parts of the circuit. But some cases require more than that. For
this applications Yosys provides commands that can be used to further inspect
the behavior of the circuit, either by evaluating which output values are
generated from certain input values (:cmd:ref:`eval`) or by evaluation which
input values and initial conditions can result in a certain behavior at the
outputs (:cmd:ref:`sat`). The SAT command can even be used to prove (or
disprove) theorems regarding the circuit, in more advanced cases with the
additional help of a miter circuit.
This features can be powerful tools for the circuit designer using Yosys
as a utility for building circuits and the software developer using

2
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@ -180,7 +180,7 @@ to the Yosys documentation, or run ``yosys -h <command_name>``.
The script presented earlier can be easily modified to have a BTOR file that
does not contain memories. This is done by removing the line number 8 and 10,
and introduces a new command ``memory`` at line number 8.
and introduces a new command :cmd:ref:`memory` at line number 8.
:numref:`btor_script_without_memory` shows the modified Yosys script file:
.. code-block:: sh

3
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@ -81,7 +81,8 @@ synthesis script (``counter.ys``), a digital design written in Verilog
#. :yoscrypt:`dfflibmap -liberty mycells.lib` - Map registers to available
hardware flip-flops.
#. :yoscrypt:`abc -liberty mycells.lib` - Map logic to available hardware gates.
#. :yoscrypt:`clean` - Clean up the design (just the last step of ``opt``).
#. :yoscrypt:`clean` - Clean up the design (just the last step of
:cmd:ref:`opt`).
#. :yoscrypt:`write_verilog synth.v` - Write final synthesis result to output
file.

16
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@ -10,10 +10,10 @@ terminated using the newline character or a semicolon (;). Empty lines and lines
starting with the hash sign (#) are ignored. See :ref:`sec:typusecase` for an
example synthesis script.
The command ``help`` can be used to access the command reference manual, with
``help <command>`` providing details for a specific command. ``yosys -H`` or
``yosys -h <command>`` will do the same outside of an interactive prompt. The
entire reference manual is also available here at :doc:`/cmd_ref`.
The command :cmd:ref:`help` can be used to access the command reference manual,
with ``help <command>`` providing details for a specific command. ``yosys -H``
or ``yosys -h <command>`` will do the same outside of an interactive prompt.
The entire reference manual is also available here at :doc:`/cmd_ref`.
Example commands
~~~~~~~~~~~~~~~~
@ -99,10 +99,10 @@ Selections intro
~~~~~~~~~~~~~~~~
Most commands can operate not only on the entire design but also specifically on
selected parts of the design. For example the command ``dump`` will print all
selected objects in the current design while ``dump foobar`` will only print the
module ``foobar`` and ``dump *`` will print the entire design regardless of the
current selection.
selected parts of the design. For example the command :cmd:ref:`dump` will print
all selected objects in the current design while ``dump foobar`` will only print
the module ``foobar`` and ``dump *`` will print the entire design regardless of
the current selection.
.. code:: yoscrypt

126
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@ -57,17 +57,17 @@ needed variations of parametric modules.
hierarchy -check -top top_module
The ``proc`` command
~~~~~~~~~~~~~~~~~~~~~~
The :cmd:ref:`proc` command
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Verilog frontend converts ``always``-blocks to RTL netlists for the
expressions and "processess" for the control- and memory elements.
The ``proc`` command transforms this "processess" to netlists of RTL multiplexer
and register cells.
The :cmd:ref:`proc` command transforms this "processess" to netlists of RTL
multiplexer and register cells.
The ``proc`` command is actually a macro-command that calls the following other
commands:
The :cmd:ref:`proc` command is actually a macro-command that calls the following
other commands:
.. code-block:: yoscrypt
@ -80,8 +80,8 @@ commands:
proc_clean # if all went fine, this should remove all the processes
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 :cmd:ref:`proc` is the first command in the actual synthesis procedure
after design elaboration.
Example
^^^^^^^
@ -120,11 +120,11 @@ Example
:caption: ``docs/resources/PRESENTATION_ExSyn/proc_03.v``
The ``opt`` command
~~~~~~~~~~~~~~~~~~~~~
The :cmd:ref:`opt` command
~~~~~~~~~~~~~~~~~~~~~~~~~~
The ``opt`` command implements a series of simple optimizations. It also is a
macro command that calls other commands:
The :cmd:ref:`opt` command implements a series of simple optimizations. It also
is a macro command that calls other commands:
.. code-block:: yoscrypt
@ -140,8 +140,8 @@ macro command that calls other commands:
opt_expr # const folding and simple expression rewriting
while [changed design]
The command ``clean`` can be used as alias for ``opt_clean``. And ``;;`` can be
used as shortcut for ``clean``. For example:
The command :cmd:ref:`clean` can be used as alias for :cmd:ref:`opt_clean`. And
``;;`` can be used as shortcut for :cmd:ref:`clean`. For example:
.. code-block:: yoscrypt
@ -195,31 +195,31 @@ Example
:caption: ``docs/resources/PRESENTATION_ExSyn/opt_04.ys``
When to use ``opt`` or ``clean``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When to use :cmd:ref:`opt` or :cmd:ref:`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 :cmd:ref:`opt` after each regular command in
the synthesis script. But it increases the synthesis time, so it is favourable
to only call :cmd:ref:`opt` when an improvement can be achieved.
The designs in ``yosys-bigsim`` are a good playground for experimenting with the
effects of calling ``opt`` in various places of the flow.
effects of calling :cmd:ref:`opt` in various places of the flow.
It generally is a good idea to call ``opt`` before inherently expensive commands
such as ``sat`` or ``freduce``, as the possible gain is much higher in this
cases as the possible loss.
It generally is a good idea to call :cmd:ref:`opt` before inherently expensive
commands such as :cmd:ref:`sat` or :cmd:ref:`freduce`, as the possible gain is
much higher in this cases as the possible loss.
The ``clean`` command 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 ``;;`` is a good
idea in every synthesis script.
The :cmd:ref:`clean` command 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
``;;`` is a good idea in every synthesis script.
The ``memory`` command
~~~~~~~~~~~~~~~~~~~~~~~~
The :cmd:ref:`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``
consolidating the number of ports for a memory easier. The :cmd:ref:`memory`
transforms memories to an implementation. Per default that is logic for address
decoders and registers. It also is a macro command that calls other commands:
@ -269,12 +269,12 @@ Example
:caption: ``docs/resources/PRESENTATION_ExSyn/memory_02.ys``
The ``fsm`` command
~~~~~~~~~~~~~~~~~~~~~
The :cmd:ref:`fsm` command
~~~~~~~~~~~~~~~~~~~~~~~~~~
The ``fsm`` command identifies, extracts, optimizes (re-encodes), and
re-synthesizes finite state machines. It again is a macro that calls
a series of other commands:
The :cmd:ref:`fsm` command identifies, extracts, optimizes (re-encodes), and
re-synthesizes finite state machines. It again is a macro that calls a series of
other commands:
.. code-block:: yoscrypt
@ -298,26 +298,27 @@ a series of other commands:
Some details on the most important commands from the ``fsm_*`` group:
The ``fsm_detect`` command identifies FSM state registers and marks them with
the ``(* fsm_encoding = "auto" *)`` attribute, if they do not have the
The :cmd:ref:`fsm_detect` command identifies FSM state registers and marks them
with the ``(* fsm_encoding = "auto" *)`` attribute, if they do not have the
``fsm_encoding`` set already. Mark registers with ``(* fsm_encoding = "none"
*)`` to disable FSM optimization for a register.
The ``fsm_extract`` command replaces the entire FSM (logic and state registers)
with a ``$fsm`` cell.
The :cmd:ref:`fsm_extract` command replaces the entire FSM (logic and state
registers) with a ``$fsm`` cell.
The commands ``fsm_opt`` and ``fsm_recode`` can be used to optimize the FSM.
The commands :cmd:ref:`fsm_opt` and :cmd:ref:`fsm_recode` can be used to
optimize the FSM.
Finally the ``fsm_map`` command can be used to convert the (optimized) ``$fsm``
cell back to logic and registers.
Finally the :cmd:ref:`fsm_map` command can be used to convert the (optimized)
``$fsm`` cell back to logic and registers.
The ``techmap`` command
~~~~~~~~~~~~~~~~~~~~~~~~~
The :cmd:ref:`techmap` command
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. figure:: ../../images/res/PRESENTATION_ExSyn/techmap_01.*
:class: width-helper
The ``techmap`` command replaces cells with implementations given as
The :cmd:ref:`techmap` command replaces cells with implementations given as
verilog source. For example implementing a 32 bit adder using 16 bit adders:
.. literalinclude:: ../../resources/PRESENTATION_ExSyn/techmap_01_map.v
@ -335,8 +336,9 @@ verilog source. For example implementing a 32 bit adder using 16 bit adders:
stdcell mapping
^^^^^^^^^^^^^^^
When ``techmap`` is used without a map file, it uses a built-in map file to map
all RTL cell types to a generic library of built-in logic gates and registers.
When :cmd:ref:`techmap` is used without a map file, it uses a built-in map file
to map all RTL cell types to a generic library of built-in logic gates and
registers.
The built-in logic gate types are: ``$_NOT_``, ``$_AND_``, ``$_OR_``,
``$_XOR_``, and ``$_MUX_``.
@ -351,26 +353,27 @@ The register types are: ``$_SR_NN_``, ``$_SR_NP_``, ``$_SR_PN_``, ``$_SR_PP_``,
See :doc:`/yosys_internals/formats/cell_library` for more about the internal
cells used.
The ``abc`` command
~~~~~~~~~~~~~~~~~~~~~
The :cmd:ref:`abc` command
~~~~~~~~~~~~~~~~~~~~~~~~~~
The ``abc`` command provides an interface to ABC_, an open source tool for
low-level logic synthesis.
The :cmd:ref:`abc` command provides an interface to ABC_, an open source tool
for low-level logic synthesis.
.. _ABC: http://www.eecs.berkeley.edu/~alanmi/abc/
The ``abc`` command processes a netlist of internal gate types and can perform:
The :cmd:ref:`abc` command processes a netlist of internal gate types and can
perform:
- logic minimization (optimization)
- mapping of logic to standard cell library (liberty format)
- mapping of logic to k-LUTs (for FPGA synthesis)
Optionally ``abc`` can process registers from one clock domain and perform
sequential optimization (such as register balancing).
Optionally :cmd:ref:`abc` can process registers from one clock domain and
perform sequential optimization (such as register balancing).
ABC is also controlled using scripts. An ABC script can be specified to use more
advanced ABC features. It is also possible to write the design with
``write_blif`` and load the output file into ABC outside of Yosys.
:cmd:ref:`write_blif` and load the output file into ABC outside of Yosys.
Example
^^^^^^^
@ -389,16 +392,16 @@ Example
Other special-purpose mapping commands
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
``dfflibmap``
:cmd:ref:`dfflibmap`
This command maps the internal register cell types to the register types
described in a liberty file.
``hilomap``
:cmd:ref:`hilomap`
Some architectures require special driver cells for driving a constant hi or
lo value. This command replaces simple constants with instances of such driver
cells.
``iopadmap``
:cmd:ref:`iopadmap`
Top-level input/outputs must usually be implemented using special I/O-pad
cells. This command inserts this cells to the design.
@ -436,5 +439,6 @@ Example Synthesis Script
# write synthesis results
write_edif synth.edif
The weird ``select`` expressions at the end of this script are discussed later
in :doc:`using_yosys/more_scripting/selections</using_yosys/more_scripting/selections>`.
The weird :cmd:ref:`select` expressions at the end of this script are discussed
later in
:doc:`using_yosys/more_scripting/selections</using_yosys/more_scripting/selections>`.

13
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@ -3,12 +3,13 @@
Memory mapping
==============
Documentation for the Yosys ``memory_libmap`` memory mapper. Note that not all supported patterns
are included in this document, of particular note is that combinations of multiple patterns should
generally work. For example, `Write port with byte enables`_ could be used in conjunction with any
of the simple dual port (SDP) models. In general if a hardware memory definition does not support a
given configuration, additional logic will be instantiated to guarantee behaviour is consistent with
simulation.
Documentation for the Yosys :cmd:ref:`memory_libmap` memory mapper. Note that
not all supported patterns are included in this document, of particular note is
that combinations of multiple patterns should generally work. For example,
`Write port with byte enables`_ could be used in conjunction with any of the
simple dual port (SDP) models. In general if a hardware memory definition does
not support a given configuration, additional logic will be instantiated to
guarantee behaviour is consistent with simulation.
See also: `passes/memory/memlib.md <https://github.com/YosysHQ/yosys/blob/master/passes/memory/memlib.md>`_

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@ -11,12 +11,13 @@ This chapter outlines these optimizations.
Simple optimizations
--------------------
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. At the time of this writing the
``opt`` pass executes the following passes that each perform a simple optimization:
The Yosys pass :cmd:ref:`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. At the time of
this writing the :cmd:ref:`opt` pass executes the following passes that each
perform a simple optimization:
- Once at the beginning of ``opt``:
- Once at the beginning of :cmd:ref:`opt`:
- ``opt_expr``
- ``opt_merge -nomux``
@ -32,15 +33,15 @@ after each major step in the synthesis script. At the time of this writing the
The following section describes each of the ``opt_`` passes.
The opt_expr pass
~~~~~~~~~~~~~~~~~
The :cmd:ref:`opt_expr` pass
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This pass performs const folding on the internal combinational cell types
described in :ref:`chapter:celllib`. This means a cell with all
constant inputs is replaced with the constant value this cell drives. In some
cases this pass can also optimize cells with some constant inputs.
described in :ref:`chapter:celllib`. This means a cell with all constant inputs
is replaced with the constant value this cell drives. In some cases this pass
can also optimize cells with some constant inputs.
.. table:: Const folding rules for ``$_AND_`` cells as used in opt_expr.
.. table:: Const folding rules for ``$_AND_`` cells as used in :cmd:ref:`opt_expr`.
:name: tab:opt_expr_and
:align: center
@ -80,15 +81,16 @@ 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 ``$ne`` cells with buffers or not-gates if one input is constant.
Besides this basic const folding the :cmd:ref:`opt_expr` pass can replace 1-bit
wide ``$eq`` and ``$ne`` cells with buffers or not-gates if one input is
constant.
The opt_expr pass is very conservative regarding optimizing ``$mux`` cells, as
these cells are often used to model decision-trees and breaking these trees can
interfere with other optimizations.
The :cmd:ref:`opt_expr` pass is very conservative regarding optimizing ``$mux``
cells, as these cells are often used to model decision-trees and breaking these
trees can interfere with other optimizations.
The opt_muxtree pass
~~~~~~~~~~~~~~~~~~~~
The :cmd:ref:`opt_muxtree` pass
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This pass optimizes trees of multiplexer cells by analyzing the select inputs.
Consider the following simple example:
@ -99,12 +101,12 @@ Consider the following simple example:
module uut(a, y); input a; output [1:0] y = a ? (a ? 1 : 2) : 3; endmodule
The output can never be 2, as this would require ``a`` to be 1 for the outer
multiplexer and 0 for the inner multiplexer. The opt_muxtree pass detects this
contradiction and replaces the inner multiplexer with a constant 1, yielding the
logic for ``y = a ? 1 : 3``.
multiplexer and 0 for the inner multiplexer. The :cmd:ref:`opt_muxtree` pass
detects this contradiction and replaces the inner multiplexer with a constant 1,
yielding the logic for ``y = a ? 1 : 3``.
The opt_reduce pass
~~~~~~~~~~~~~~~~~~~
The :cmd:ref:`opt_reduce` pass
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This is a simple optimization pass that identifies and consolidates identical
input bits to ``$reduce_and`` and ``$reduce_or`` cells. It also sorts the input
@ -121,22 +123,22 @@ Lastly this pass consolidates trees of ``$reduce_and`` cells and trees of
These three simple optimizations are performed in a loop until a stable result
is produced.
The opt_rmdff pass
~~~~~~~~~~~~~~~~~~
The :cmd:ref:`opt_rmdff` pass
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This pass identifies single-bit d-type flip-flops (``$_DFF_``, ``$dff``, and
``$adff`` cells) with a constant data input and replaces them with a constant
driver.
The opt_clean pass
~~~~~~~~~~~~~~~~~~
The :cmd:ref:`opt_clean` pass
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This pass identifies unused signals and cells and removes them from the design.
It also creates an ``\unused_bits`` attribute on wires with unused bits. This
attribute can be used for debugging or by other optimization passes.
The opt_merge pass
~~~~~~~~~~~~~~~~~~
The :cmd:ref:`opt_merge` pass
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This pass performs trivial resource sharing. This means that this pass
identifies cells with identical inputs and replaces them with a single instance
@ -144,8 +146,8 @@ of the cell.
The option ``-nomux`` can be used to disable resource sharing for multiplexer
cells (``$mux`` and ``$pmux``.) This can be useful as it prevents multiplexer
trees to be merged, which might prevent ``opt_muxtree`` to identify possible
optimizations.
trees to be merged, which might prevent :cmd:ref:`opt_muxtree` to identify
possible optimizations.
FSM extraction and encoding
---------------------------
@ -193,9 +195,9 @@ using the ``\fsm_encoding`` attribute (unless ``\fsm_encoding`` is set to
``fsm_`` passes operate on these ``$fsm`` cells. The fsm_map call finally
replaces the ``$fsm`` cells with RTL cells.
Note that these optimizations operate on an RTL netlist. I.e. the ``fsm`` pass
should be executed after the proc pass has transformed all ``RTLIL::Process``
objects to RTL cells.
Note that these optimizations operate on an RTL netlist. I.e. the :cmd:ref:`fsm`
pass should be executed after the proc pass has transformed all
``RTLIL::Process`` objects to RTL cells.
The algorithms used for FSM detection and extraction are influenced by a more
general reported technique :cite:p:`fsmextract`.
@ -295,8 +297,8 @@ The fsm_opt pass performs basic optimizations on ``$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 :cmd:ref:`opt_clean` pass) is
used to determine which control outputs are unused.
- Control inputs that are connected to the same driver are merged.

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@ -12,7 +12,7 @@ used to apply commands only to part of the design. For example:
delete foobar # will only delete the module foobar.
The ``select`` command can be used to create a selection for subsequent
The :cmd:ref:`select` command can be used to create a selection for subsequent
commands. For example:
.. code:: yoscrypt
@ -42,8 +42,8 @@ in synthesis scripts that are hand-tailored for a specific design.
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
Commands can be executed in *module/* or *design/* context. Until now all
commands have been executed in design context. The :cmd:ref:`cd` command can be
used to switch to module context.
In module context all commands only effect the active module. Objects in the
@ -76,7 +76,7 @@ Special patterns can be used to select by object property or type. For example:
select foo/t:$add # select all $add cells from the module foo
A complete list of this pattern expressions can be found in the command
reference to the ``select`` command.
reference to the :cmd:ref:`select` command.
Combining selection
^^^^^^^^^^^^^^^^^^^
@ -190,12 +190,13 @@ Interactive Design Investigation
Yosys can also be used to investigate designs (or netlists created from other
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.
- 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 :cmd:ref:`submod`, :cmd:ref:`expose`, and :cmd:ref:`splice`
can be used to transform the design into an equivalent design that is easier
to analyse.
- Commands such as :cmd:ref:`eval` and :cmd:ref:`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
@ -204,10 +205,10 @@ tools).
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
engineering and analysis. An example using ``submod`` is shown below for
Commands such as :cmd:ref:`flatten` and :cmd:ref:`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 :cmd:ref:`submod` is shown below for
reorganizing a module in Yosys and checking the resulting circuit.
.. literalinclude:: ../../../resources/PRESENTATION_ExOth/scrambler.v
@ -254,10 +255,10 @@ 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 :cmd:ref:`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
@ -289,6 +290,5 @@ Yosys script for ASIC synthesis of the Amber ARMv2 CPU.
endmodule
For more on the ``techmap`` command, see the page on
:doc:`/yosys_internals/techmap` or the
:doc:`techmap command reference document</cmd/techmap>`.
For more on the :cmd:ref:`techmap` command, see the page on
:doc:`/yosys_internals/techmap`.

2
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@ -1,7 +1,7 @@
Introduction to synthesis
-------------------------
The following commands are executed by the ``synth`` command:
The following commands are executed by the :cmd:ref:`synth` command:
.. literalinclude:: /cmd/synth.rst
:start-at: begin:

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@ -58,7 +58,7 @@ about the internal data storage format used in Yosys and the classes that it
provides.
This document will focus on the much simpler version of RTLIL left after the
commands ``proc`` and ``memory`` (or ``memory -nomap``):
commands :cmd:ref:`proc` and :cmd:ref:`memory` (or ``memory -nomap``):
.. figure:: ../../images/simplified_rtlil.*
:class: width-helper
@ -77,9 +77,10 @@ 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. The :doc:`/using_yosys/more_scripting/selections`
document has more information on using these commands.
look at the output of :cmd:ref:`dump` and :cmd:ref:`show` before and after the
command has been executed can be helpful. The
:doc:`/using_yosys/more_scripting/selections` document has more information on
using these commands.
.. todo:: copypaste
@ -120,15 +121,16 @@ 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
:cmd:ref:`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,
but be careful when changing the size of the ``SigSpec`` connected to a cell
port.
- Use the ``SigMap`` helper class (see next slide) when you need a unique handle for each signal bit.
- Use the ``SigMap`` helper class (see next section) when you need a unique
handle for each signal bit.
Using the SigMap helper class
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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@ -28,13 +28,13 @@ components, such as LUTs, gates, or half- and full-adders.
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.
- In a way the ``extract`` pass is the inverse of the techmap pass.
- Like the :cmd:ref:`techmap` pass, the :cmd:ref:`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 :cmd:ref:`extract` pass will replace the matching
subcircuit with an instance of the module from the map file.
- In a way the :cmd:ref:`extract` pass is the inverse of the techmap pass.
.. todo:: copypaste
@ -93,19 +93,19 @@ 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.
Identify candidate-cells in the circuit and wrap them in a cell with a
constant wider bit-width using :cmd:ref:`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 :cmd:ref:`extract` command can be used to replace circuits with
cells of the target architecture.
unwrap
The remaining wrapper cell can be unwrapped using ``techmap``.
The remaining wrapper cell can be unwrapped using :cmd:ref:`techmap`.
Example: DSP48_MACC
~~~~~~~~~~~~~~~~~~~
@ -144,7 +144,8 @@ Extract: ``macc_xilinx_xmap.v``
:language: verilog
:caption: ``docs/resources/PRESENTATION_ExAdv/macc_xilinx_xmap.v``
... simply use the same wrapping commands on this module as on the design to create a template for the ``extract`` command.
... simply use the same wrapping commands on this module as on the design to
create a template for the :cmd:ref:`extract` command.
Unwrapping multipliers: ``macc_xilinx_unwrap_map.v``

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@ -17,7 +17,8 @@ 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 :cmd:ref:`sat` command in Yosys can be used to perform Symbolic Model
Checking.
Checking techmap
~~~~~~~~~~~~~~~~

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@ -407,9 +407,9 @@ transformed into a set of d-type flip-flops and the
multiplexers.
In more complex examples (e.g. asynchronous resets) the part of the
``RTLIL::CaseRule``/``RTLIL::SwitchRule`` tree that describes the
asynchronous reset must first be transformed to the correct
``RTLIL::SyncRule`` objects. This is done by the proc_adff pass.
``RTLIL::CaseRule``/``RTLIL::SwitchRule`` tree that describes the asynchronous
reset must first be transformed to the correct ``RTLIL::SyncRule`` objects. This
is done by the :cmd:ref:`proc_adff` pass.
The ProcessGenerator algorithm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@ -591,16 +591,16 @@ 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
:cmd:ref:`proc` pass and the passes it launches:
- | proc_clean and proc_rmdead
- | :cmd:ref:`proc_clean` and :cmd:ref:`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.
:cmd:ref:`proc_clean` pass removes empty parts (eg. empty assignments) from
the process and :cmd:ref:`proc_rmdead` detects and removes unreachable
branches from the process's decision trees.
- | proc_arst
- | :cmd:ref:`proc_arst`
| This pass detects processes that describe d-type flip-flops with
asynchronous resets and rewrites the process to better reflect what they
are modelling: Before this pass, an asynchronous reset has two
@ -608,22 +608,22 @@ pass and the passes it launches:
reset path. After this pass the sync rule for the reset is level-sensitive
and the top-level ``RTLIL::SwitchRule`` has been removed.
- | proc_mux
- | :cmd:ref:`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.
- | proc_dff
- | :cmd:ref:`proc_dff`
| This pass replaces the ``RTLIL::SyncRule`` s to d-type flip-flops (with
asynchronous resets if necessary).
- | proc_dff
- | :cmd:ref:`proc_dff`
| 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.
- | :cmd:ref:`proc_clean`
| A final call to :cmd:ref:`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:

57
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@ -255,8 +255,8 @@ 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 :cmd:ref:`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
@ -270,8 +270,8 @@ additional two parameters:
``\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
@ -433,16 +433,17 @@ The ``$memwr_v2`` cells have a clock input ``\CLK``, an enable input ``\EN``
``1'b1`` and on the negative edge if this parameter is ``1'b0``.
``\PORTID``
An identifier for this write port, used to index write port bit mask parameters.
An identifier for this write port, used to index write port bit mask
parameters.
``\PRIORITY_MASK``
This parameter is a bitmask of write ports that this write port has
priority over in case of writing to the same address. The bits of this
parameter are indexed by the other write port's ``\PORTID`` parameter.
Write ports can only have priority over write ports with lower port ID.
When two ports write to the same address and neither has priority over
the other, the result is undefined. Priority can only be set between
two synchronous ports sharing the same clock domain.
This parameter is a bitmask of write ports that this write port has priority
over in case of writing to the same address. The bits of this parameter are
indexed by the other write port's ``\PORTID`` parameter. Write ports can
only have priority over write ports with lower port ID. When two ports write
to the same address and neither has priority over the other, the result is
undefined. Priority can only be set between two synchronous ports sharing
the same clock domain.
The ``$meminit_v2`` cells have an address input ``\ADDR``, a data input
``\DATA``, with the width of the ``\DATA`` port equal to ``\WIDTH`` parameter
@ -468,13 +469,13 @@ 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.
``$memrd_v2`` and ``$memwr_v2`` cells. The :cmd:ref:`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 ``$mem_v2`` cell provides the following parameters:
@ -600,15 +601,15 @@ The ``$mem_v2`` cell has the following 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 :cmd:ref:`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 :cmd:ref:`memory_unpack` pass
performs the inverse operation. The :cmd:ref:`memory_dff` pass can combine
asynchronous memory ports that are fed by or feeding registers into synchronous
memory ports. The :cmd:ref:`memory_bram` pass can be used to recognize
``$mem_v2`` cells that can be implemented with a block RAM resource on an FPGA.
The :cmd:ref:`memory_map` pass can be used to implement ``$mem_v2`` cells as
basic logic: word-wide DFFs and address decoders.
Finite state machines
~~~~~~~~~~~~~~~~~~~~~

46
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@ -6,22 +6,22 @@ representation. The only exception are the high-level frontends that use the AST
representation as an intermediate step before generating RTLIL data.
In order to avoid reinventing names for the RTLIL classes, they are simply
referred to by their full C++ name, i.e. including the ``RTLIL::`` namespace prefix,
in this document.
referred to by their full C++ name, i.e. including the ``RTLIL::`` namespace
prefix, in this document.
:numref:`Figure %s <fig:Overview_RTLIL>` shows a simplified Entity-Relationship
Diagram (ER Diagram) of RTLIL. In :math:`1:N` relationships the arrow points
from the :math:`N` side to the :math:`1`. For example one ``RTLIL::Design`` contains
:math:`N` (zero to many) instances of ``RTLIL::Module`` . A two-pointed arrow
indicates a :math:`1:1` relationship.
from the :math:`N` side to the :math:`1`. For example one ``RTLIL::Design``
contains :math:`N` (zero to many) instances of ``RTLIL::Module`` . A two-pointed
arrow indicates a :math:`1:1` relationship.
The ``RTLIL::Design`` is the root object of the RTLIL data structure. There is
always one "current design" in memory which passes operate on, frontends add
data to and backends convert to exportable formats. But in some cases passes
internally generate additional ``RTLIL::Design`` objects. For example when a pass is
reading an auxiliary Verilog file such as a cell library, it might create an
additional ``RTLIL::Design`` object and call the Verilog frontend with this other
object to parse the cell library.
internally generate additional ``RTLIL::Design`` objects. For example when a
pass is reading an auxiliary Verilog file such as a cell library, it might
create an additional ``RTLIL::Design`` object and call the Verilog frontend with
this other object to parse the cell library.
.. figure:: ../../../images/overview_rtlil.*
:class: width-helper
@ -31,9 +31,9 @@ object to parse the cell library.
There is only one active ``RTLIL::Design`` object that is used by all frontends,
passes and backends called by the user, e.g. using a synthesis script. The
``RTLIL::Design`` then contains zero to many ``RTLIL::Module`` objects. This corresponds
to modules in Verilog or entities in VHDL. Each module in turn contains objects
from three different categories:
``RTLIL::Design`` then contains zero to many ``RTLIL::Module`` objects. This
corresponds to modules in Verilog or entities in VHDL. Each module in turn
contains objects from three different categories:
- ``RTLIL::Cell`` and ``RTLIL::Wire`` objects represent classical netlist data.
@ -44,8 +44,8 @@ from three different categories:
- ``RTLIL::Memory`` objects represent addressable memories (arrays).
Usually the output of the synthesis procedure is a netlist, i.e. all
``RTLIL::Process`` and ``RTLIL::Memory`` objects must be replaced by ``RTLIL::Cell`` and
``RTLIL::Wire`` objects by synthesis passes.
``RTLIL::Process`` and ``RTLIL::Memory`` objects must be replaced by
``RTLIL::Cell`` and ``RTLIL::Wire`` objects by synthesis passes.
All features of the HDL that cannot be mapped directly to these RTLIL classes
must be transformed to an RTLIL-compatible representation by the HDL frontend.
@ -78,9 +78,9 @@ 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 the ``opt_rmunused`` 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.
example the :cmd:ref:`opt_rmunused` 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.
- Third, the delicate job of finding suitable auto-generated public visible
names is deferred to one central location. Internally auto-generated names
@ -184,8 +184,8 @@ An ``RTLIL::Cell`` object has the following properties:
- A list of parameters (for parametric cells)
- Cell ports and the connections of ports to wires and constants
The connections of ports to wires are coded by assigning an ``RTLIL::SigSpec`` to
each cell port. The ``RTLIL::SigSpec`` data type is described in the next
The connections of ports to wires are coded by assigning an ``RTLIL::SigSpec``
to each cell port. The ``RTLIL::SigSpec`` data type is described in the next
section.
.. _sec:rtlil_sigspec:
@ -320,8 +320,8 @@ 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 :cmd:ref:`proc_arst` pass. This pass transforms the above example to the
following ``RTLIL::Process``:
.. code:: RTLIL
:number-lines:
@ -381,8 +381,8 @@ synthesis tasks.
RTLIL::Memory
-------------
For every array (memory) in the HDL code an ``RTLIL::Memory`` object is created. A
memory object has the following properties:
For every array (memory) in the HDL code an ``RTLIL::Memory`` object is created.
A memory object has the following properties:
- The memory name
- A list of attributes

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@ -111,10 +111,9 @@ Techmap by example
.. todo:: copypaste
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 ``$or``) as well as user-defined cell
types.
As a quick recap, the :cmd:ref:`techmap` command replaces cells in the design
with implementations given as Verilog code (called "map files"). It can replace
Yosys' internal cell types (such as ``$or``) as well as user-defined cell types.
- Verilog parameters are used extensively to customize the internal cell types.
- Additional special parameters are used by techmap to communicate meta-data to
@ -188,14 +187,15 @@ Scripting in map modules
- You can even call techmap recursively!
- Example use-cases:
- Using always blocks in map module: call ``proc``
- Perform expensive optimizations (such as ``freduce``) on cells where
this is known to work well.
- Using always blocks in map module: call :cmd:ref:`proc`
- Perform expensive optimizations (such as :cmd:ref:`freduce`) on cells
where this is known to work well.
- Interacting with custom commands.
.. note:: PROTIP:
Commands such as ``shell``, ``show -pause``, and ``dump`` can be use
in the ``_TECHMAP_DO_*`` scripts for debugging map modules.
Commands such as :cmd:ref:`shell`, ``show -pause``, and :cmd:ref:`dump` can
be used in the ``_TECHMAP_DO_*`` scripts for debugging map modules.
Example: