mirror of https://github.com/YosysHQ/yosys.git
Removing typical phases doc
Moved remaining content into relevant places. Added `load_design.rst` to more scripting. Split fsm handling and abc out of optimization passes. Also moved things around to match the general flow previously described. Changed generic `synth` for `prep` instead.
This commit is contained in:
Krystine Sherwin
parent
f9ce3d1c26
commit
1e3b90ae56
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@ -1,17 +1,35 @@
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Synthesis starter
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-----------------
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..
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Typical phases of a synthesis flow are as follows:
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- Reading and elaborating the design
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- Higher-level synthesis and optimization
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- Converting ``always``-blocks to logic and registers
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- Perform coarse-grain optimizations (resource sharing, const folding, ...)
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- Handling of memories and other coarse-grain blocks
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- Extracting and optimizing finite state machines
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- Convert remaining logic to bit-level logic functions
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- Perform optimizations on bit-level logic functions
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- Map bit-level logic gates and registers to cell library
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- Write results to output file
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A simple counter
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~~~~~~~~~~~~~~~~
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.. role:: yoscrypt(code)
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:language: yoscrypt
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This section covers an example project available in
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``docs/source/code_examples/intro/*``. The project contains a simple ASIC
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This section covers an `example project`_ available in
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``docs/source/code_examples/intro/``. The project contains a simple ASIC
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synthesis script (``counter.ys``), a digital design written in Verilog
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(``counter.v``), and a simple CMOS cell library (``mycells.lib``).
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.. _example project: https://github.com/YosysHQ/yosys/tree/krys/docs/docs/source/code_examples/intro
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First, let's quickly look at the design:
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.. literalinclude:: /code_examples/intro/counter.v
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@ -159,20 +177,27 @@ Some of the commands we might use here are:
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- :doc:`/cmd/memory`,
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- :doc:`/cmd/wreduce`,
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- :doc:`/cmd/peepopt`,
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- :doc:`/cmd/pmuxtree`,
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- :doc:`/cmd/alumacc`, and
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- :doc:`/cmd/share`.
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Techmap
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~~~~~~~
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We could have also
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Logic gate mapping
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~~~~~~~~~~~~~~~~~~
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:yoscrypt:`techmap` - Map coarse-grain RTL cells (adders, etc.) to fine-grain
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logic gates (AND, OR, NOT, etc.).
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.. literalinclude:: /code_examples/intro/counter.ys
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:language: yoscrypt
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:lines: 8-9
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When :cmd:ref:`techmap` is used without a map file, it uses a built-in map file
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to map all RTL cell types to a generic library of built-in logic gates and
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registers.
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Result:
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The built-in logic gate types are: ``$_NOT_``, ``$_AND_``, ``$_OR_``,
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``$_XOR_``, and ``$_MUX_``.
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See :doc:`/yosys_internals/formats/cell_library` for more about the internal
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cells used.
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.. figure:: /_images/code_examples/intro/counter_02.*
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:class: width-helper
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@ -193,6 +218,22 @@ Mapping to hardware
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``counter`` after hardware cell mapping
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:cmd:ref:`dfflibmap`
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This command maps the internal register cell types to the register types
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described in a liberty file.
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:cmd:ref:`hilomap`
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Some architectures require special driver cells for driving a constant hi or
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lo value. This command replaces simple constants with instances of such
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driver cells.
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:cmd:ref:`iopadmap`
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Top-level input/outputs must usually be implemented using special I/O-pad
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cells. This command inserts such cells to the design.
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:cmd:ref:`dfflegalize`
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Specify a set of supported FF cells/cell groups and convert all FFs to them.
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.. _cmos_lib:
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The CMOS cell library
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@ -215,3 +256,4 @@ The script file
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:language: yoscrypt
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:caption: ``docs/source/code_examples/intro/counter.ys``
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See also :doc:`/using_yosys/synthesis/synth`.
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@ -1,457 +0,0 @@
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Typical phases of a synthesis flow
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----------------------------------
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.. role:: yoscrypt(code)
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:language: yoscrypt
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.. todo:: should e.g. :yoscrypt:`proc` and :yoscrypt:`memory` examples be
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included here (typical phases) or examples
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.. todo:: expand bullet points
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- Reading and elaborating the design
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- Higher-level synthesis and optimization
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- Converting ``always``-blocks to logic and registers
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- Perform coarse-grain optimizations (resource sharing, const folding, ...)
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- Handling of memories and other coarse-grain blocks
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- Extracting and optimizing finite state machines
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- Convert remaining logic to bit-level logic functions
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- Perform optimizations on bit-level logic functions
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- Map bit-level logic gates and registers to cell library
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- Write results to output file
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Reading the design
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~~~~~~~~~~~~~~~~~~
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.. todo:: include ``read_verilog <<EOF`` when discussing how to read designs?
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.. code-block:: yoscrypt
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read_verilog file1.v
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read_verilog -I include_dir -D enable_foo -D WIDTH=12 file2.v
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read_verilog -lib cell_library.v
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verilog_defaults -add -I include_dir
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read_verilog file3.v
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read_verilog file4.v
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verilog_defaults -clear
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verilog_defaults -push
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verilog_defaults -add -I include_dir
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read_verilog file5.v
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read_verilog file6.v
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verilog_defaults -pop
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Design elaboration
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~~~~~~~~~~~~~~~~~~
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During design elaboration Yosys figures out how the modules are hierarchically
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connected. It also re-runs the AST parts of the Verilog frontend to create all
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needed variations of parametric modules.
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.. todo:: hierarchy without ``-top`` is bad
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- resolve non-module-specific references (sub modules, interfaces et al)
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- check sub modules exist, discarding unused
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- set top attribute
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- also mention failure modes
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- also prep?
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.. code-block:: yoscrypt
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# simplest form. at least this version should be used after reading all input files
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#
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hierarchy
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# recommended form. fails if parts of the design hierarchy are missing, removes
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# everything that is unreachable from the top module, and marks the top module.
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#
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hierarchy -check -top top_module
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Converting process blocks
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~~~~~~~~~~~~~~~~~~~~~~~~~
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The Verilog frontend converts ``always``-blocks to RTL netlists for the
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expressions and "processess" for the control- and memory elements. The
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:cmd:ref:`proc` command then transforms these "processess" to netlists of RTL
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multiplexer and register cells. It also is a macro command that calls the other
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``proc_*`` commands in a sensible order:
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#. :cmd:ref:`proc_clean` removes empty branches and processes.
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#. :cmd:ref:`proc_rmdead` removes unreachable branches.
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#. :cmd:ref:`proc_prune`
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#. :cmd:ref:`proc_init` special handling of "initial" blocks.
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#. :cmd:ref:`proc_arst` identifies modeling of async resets.
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#. :cmd:ref:`proc_rom`
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#. :cmd:ref:`proc_mux` converts decision trees to multiplexer networks.
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#. :cmd:ref:`proc_dlatch`
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#. :cmd:ref:`proc_dff` extracts registers from processes.
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#. :cmd:ref:`proc_memwr`
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#. :cmd:ref:`proc_clean` this should remove all the processes, provided all went
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fine.
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After all the ``proc_*`` commands, :yoscrypt:`opt_expr` is called. This can be
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disabled by calling :yoscrypt:`proc -noopt`. For more information about
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:cmd:ref:`proc`, such as disabling certain sub commands, see :doc:`/cmd/proc`.
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Many commands can not operate on modules with "processess" in them. Usually a
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call to :cmd:ref:`proc` is the first command in the actual synthesis procedure
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after design elaboration.
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Example
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^^^^^^^
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.. todo:: describe ``proc`` images
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.. literalinclude:: /code_examples/synth_flow/proc_01.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/proc_01.v``
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.. literalinclude:: /code_examples/synth_flow/proc_01.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/proc_01.ys``
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.. figure:: /_images/code_examples/synth_flow/proc_01.*
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:class: width-helper
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.. figure:: /_images/code_examples/synth_flow/proc_02.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/proc_02.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/proc_02.v``
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.. literalinclude:: /code_examples/synth_flow/proc_02.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/proc_02.ys``
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.. figure:: /_images/code_examples/synth_flow/proc_03.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/proc_03.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/proc_03.ys``
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.. literalinclude:: /code_examples/synth_flow/proc_03.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/proc_03.v``
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Optimizations
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~~~~~~~~~~~~~
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The :cmd:ref:`opt` command implements a series of simple optimizations. It also
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is a macro command that calls other commands:
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.. code-block:: yoscrypt
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opt_expr # const folding and simple expression rewriting
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opt_merge -nomux # merging identical cells
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do
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opt_muxtree # remove never-active branches from multiplexer tree
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opt_reduce # consolidate trees of boolean ops to reduce functions
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opt_merge # merging identical cells
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opt_rmdff # remove/simplify registers with constant inputs
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opt_clean # remove unused objects (cells, wires) from design
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opt_expr # const folding and simple expression rewriting
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while [changed design]
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The command :cmd:ref:`clean` can be used as alias for :cmd:ref:`opt_clean`. And
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``;;`` can be used as shortcut for :cmd:ref:`clean`. For example:
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.. code-block:: yoscrypt
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hierarchy; proc; opt; memory; opt_expr;; fsm;;
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Example
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^^^^^^^
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.. todo:: describe ``opt`` images
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.. figure:: /_images/code_examples/synth_flow/opt_01.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/opt_01.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/opt_01.ys``
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.. literalinclude:: /code_examples/synth_flow/opt_01.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/opt_01.v``
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.. figure:: /_images/code_examples/synth_flow/opt_02.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/opt_02.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/opt_02.ys``
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.. literalinclude:: /code_examples/synth_flow/opt_02.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/opt_02.v``
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.. figure:: /_images/code_examples/synth_flow/opt_03.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/opt_03.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/opt_03.ys``
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.. literalinclude:: /code_examples/synth_flow/opt_03.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/opt_03.v``
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.. figure:: /_images/code_examples/synth_flow/opt_04.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/opt_04.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/opt_04.v``
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.. literalinclude:: /code_examples/synth_flow/opt_04.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/opt_04.ys``
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When to use :cmd:ref:`opt` or :cmd:ref:`clean`
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Usually it does not hurt to call :cmd:ref:`opt` after each regular command in
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the synthesis script. But it increases the synthesis time, so it is favourable
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to only call :cmd:ref:`opt` when an improvement can be achieved.
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It is generally a good idea to call :cmd:ref:`opt` before inherently expensive
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commands such as :cmd:ref:`sat` or :cmd:ref:`freduce`, as the possible gain is
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much higher in these cases as the possible loss.
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The :cmd:ref:`clean` command on the other hand is very fast and many commands
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leave a mess (dangling signal wires, etc). For example, most commands do not
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remove any wires or cells. They just change the connections and depend on a
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later call to clean to get rid of the now unused objects. So the occasional
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``;;`` is a good idea in every synthesis script.
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Other common optimization commands
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. todo:: fill out descriptions for other optimization commands
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:cmd:ref:`wreduce`
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Reduces the word size of operations.
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:cmd:ref:`peepopt`
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Applies a collection of peephole optimizers to the current design.
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:cmd:ref:`share`
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Merges shareable resources into a single resource using a SAT solver to
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determine if two resources are shareable.
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Memory handling
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~~~~~~~~~~~~~~~
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In the RTL netlist, memory reads and writes are individual cells. This makes
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consolidating the number of ports for a memory easier. The :cmd:ref:`memory`
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transforms memories to an implementation. Per default that is logic for address
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decoders and registers. It also is a macro command that calls the other
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``memory_*`` commands in a sensible order:
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.. todo:: fill out missing :cmd:ref:`memory` subcommands descriptions
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#. :cmd:ref:`memory_bmux2rom`
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#. :cmd:ref:`memory_dff` merges registers into the memory read- and write cells.
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#. :cmd:ref:`memory_share`
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#. :cmd:ref:`memory_memx`
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#. :cmd:ref:`memory_collect` collects all read and write cells for a memory and
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transforms them into one multi-port memory cell.
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#. :cmd:ref:`memory_bram`
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#. :cmd:ref:`memory_map` takes the multi-port memory cell and transforms it to
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address decoder logic and registers.
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.. todo:: is :yoscrypt:`memory -nomap; techmap -map my_memory_map.v; memory_map`
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superceded by :yoscrypt:`memory_libmap`?
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Usually it is preferred to use architecture-specific RAM resources for memory.
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For example:
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.. code-block:: yoscrypt
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memory -nomap; techmap -map my_memory_map.v; memory_map
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For more information about :cmd:ref:`memory`, such as disabling certain sub
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commands, see :doc:`/cmd/memory`.
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Example
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^^^^^^^
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.. todo:: describe ``memory`` images
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.. figure:: /_images/code_examples/synth_flow/memory_01.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/memory_01.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/memory_01.ys``
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.. literalinclude:: /code_examples/synth_flow/memory_01.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/memory_01.v``
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.. figure:: /_images/code_examples/synth_flow/memory_02.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/memory_02.v
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:language: verilog
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:caption: ``docs/source/code_examples/synth_flow/memory_02.v``
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.. literalinclude:: /code_examples/synth_flow/memory_02.ys
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:language: yoscrypt
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:caption: ``docs/source/code_examples/synth_flow/memory_02.ys``
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The :cmd:ref:`memory_libmap` command
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. todo:: :cmd:ref:`memory_libmap` description
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FSM handling
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~~~~~~~~~~~~
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The :cmd:ref:`fsm` command identifies, extracts, optimizes (re-encodes), and
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re-synthesizes finite state machines. It again is a macro that calls a series of
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other commands:
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#. :cmd:ref:`fsm_detect` identifies FSM state registers and marks them
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with the ``(* fsm_encoding = "auto" *)`` attribute, if they do not have the
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``fsm_encoding`` set already. Mark registers with ``(* fsm_encoding = "none"
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*)`` to disable FSM optimization for a register.
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#. :cmd:ref:`fsm_extract` replaces the entire FSM (logic and state registers)
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with a ``$fsm`` cell.
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#. :cmd:ref:`fsm_opt` optimizes the FSM. Called multiple times.
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#. :cmd:ref:`fsm_expand` optionally merges additional auxilliary gates into the
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``$fsm`` cell.
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#. :cmd:ref:`fsm_recode` also optimizes the FSM.
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#. :cmd:ref:`fsm_info` logs internal FSM information.
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#. :cmd:ref:`fsm_export` optionally exports each FSM to KISS2 files.
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#. :cmd:ref:`fsm_map` converts the (optimized) ``$fsm`` cell back to logic and
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registers.
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See also :doc:`/cmd/fsm`.
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DSP handling
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~~~~~~~~~~~~
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.. todo:: add info about dsp handling
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Technology mapping
|
||||
~~~~~~~~~~~~~~~~~~
|
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The :cmd:ref:`techmap` command replaces cells with implementations given as
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verilog source. For example implementing a 32 bit adder using 16 bit adders:
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.. figure:: /_images/code_examples/synth_flow/techmap_01.*
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:class: width-helper
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.. literalinclude:: /code_examples/synth_flow/techmap_01_map.v
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:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/techmap_01_map.v``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/techmap_01.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/techmap_01.v``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/techmap_01.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/techmap_01.ys``
|
||||
|
||||
See :doc:`/yosys_internals/techmap` for more.
|
||||
|
||||
stdcell mapping
|
||||
^^^^^^^^^^^^^^^
|
||||
|
||||
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 ``$_MUX_``.
|
||||
|
||||
The register types are: ``$_SR_NN_``, ``$_SR_NP_``, ``$_SR_PN_``, ``$_SR_PP_``,
|
||||
``$_DFF_N_``, ``$_DFF_P_ $_DFF_NN0_``, ``$_DFF_NN1_``, ``$_DFF_NP0_``,
|
||||
``$_DFF_NP1_``, ``$_DFF_PN0_``, ``$_DFF_PN1_``, ``$_DFF_PP0_ $_DFF_PP1_``,
|
||||
``$_DFFSR_NNN_``, ``$_DFFSR_NNP_``, ``$_DFFSR_NPN_``, ``$_DFFSR_NPP_``,
|
||||
``$_DFFSR_PNN_ $_DFFSR_PNP_``, ``$_DFFSR_PPN_``, ``$_DFFSR_PPP_``,
|
||||
``$_DLATCH_N_``, and ``$_DLATCH_P_``.
|
||||
|
||||
See :doc:`/yosys_internals/formats/cell_library` for more about the internal
|
||||
cells used.
|
||||
|
||||
The :cmd:ref:`abc` command
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
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 :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 :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
|
||||
:cmd:ref:`write_blif` and load the output file into ABC outside of Yosys.
|
||||
|
||||
Example
|
||||
^^^^^^^
|
||||
|
||||
.. todo:: describe ``abc`` images
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/abc_01.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/abc_01.v``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/abc_01.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/abc_01.ys``
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/abc_01.*
|
||||
:class: width-helper
|
||||
|
||||
Other special-purpose mapping commands
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
The commands below may be used depending on the targeted architecture for
|
||||
compatibility with, or to take advantage of, resources available.
|
||||
|
||||
:cmd:ref:`dfflibmap`
|
||||
This command maps the internal register cell types to the register types
|
||||
described in a liberty file.
|
||||
|
||||
: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.
|
||||
|
||||
:cmd:ref:`iopadmap`
|
||||
Top-level input/outputs must usually be implemented using special I/O-pad
|
||||
cells. This command inserts such cells to the design.
|
||||
|
||||
:cmd:ref:`alumacc`
|
||||
Translate arithmetic operations like $add, $mul, $lt, etc. to $alu and $macc
|
||||
cells.
|
||||
|
||||
:cmd:ref:`dfflegalize`
|
||||
Specify a set of supported FF cells/cell groups and convert all FFs to them.
|
||||
|
||||
:cmd:ref:`deminout`
|
||||
Convert inout ports to input or output ports, if possible.
|
||||
|
||||
:cmd:ref:`pmuxtree`
|
||||
Transforms parallel mux cells, ``$pmux``, to trees of ``$mux`` cells.
|
||||
|
|
@ -2,8 +2,9 @@ More scripting
|
|||
--------------
|
||||
|
||||
.. toctree::
|
||||
:maxdepth: 3
|
||||
:maxdepth: 3
|
||||
|
||||
selections
|
||||
interactive_investigation
|
||||
troubleshooting
|
||||
load_design
|
||||
selections
|
||||
interactive_investigation
|
||||
troubleshooting
|
||||
|
|
|
|||
|
|
@ -0,0 +1,37 @@
|
|||
Loading a design
|
||||
~~~~~~~~~~~~~~~~
|
||||
|
||||
keyword: Frontends
|
||||
|
||||
- :doc:`/cmd/read_verilog`
|
||||
|
||||
.. todo:: include ``read_verilog <<EOF``, also other methods of loading designs
|
||||
|
||||
.. code-block:: yoscrypt
|
||||
|
||||
read_verilog file1.v
|
||||
read_verilog -I include_dir -D enable_foo -D WIDTH=12 file2.v
|
||||
read_verilog -lib cell_library.v
|
||||
|
||||
verilog_defaults -add -I include_dir
|
||||
read_verilog file3.v
|
||||
read_verilog file4.v
|
||||
verilog_defaults -clear
|
||||
|
||||
verilog_defaults -push
|
||||
verilog_defaults -add -I include_dir
|
||||
read_verilog file5.v
|
||||
read_verilog file6.v
|
||||
verilog_defaults -pop
|
||||
|
||||
Others:
|
||||
|
||||
- :doc:`/cmd/read`
|
||||
- `GHDL plugin`_ for VHDL
|
||||
- :doc:`/cmd/read_rtlil` (direct textual representation of Yosys internal state)
|
||||
- :doc:`/cmd/read_aiger`
|
||||
- :doc:`/cmd/read_blif`
|
||||
- :doc:`/cmd/read_json`
|
||||
- :doc:`/cmd/read_liberty`
|
||||
|
||||
.. _GHDL plugin: https://github.com/ghdl/ghdl-yosys-plugin
|
||||
|
|
@ -0,0 +1,39 @@
|
|||
The :cmd:ref:`abc` command
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
.. todo:: discuss abc (more stable) vs abc9 (newer, possibly better)
|
||||
|
||||
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 :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 :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
|
||||
:cmd:ref:`write_blif` and load the output file into ABC outside of Yosys.
|
||||
|
||||
Example
|
||||
^^^^^^^
|
||||
|
||||
.. todo:: describe ``abc`` images
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/abc_01.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/abc_01.v``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/abc_01.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/abc_01.ys``
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/abc_01.*
|
||||
:class: width-helper
|
||||
|
|
@ -1,160 +1,26 @@
|
|||
.. _chapter:opt:
|
||||
FSM handling
|
||||
============
|
||||
|
||||
Optimization passes
|
||||
===================
|
||||
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:
|
||||
|
||||
.. todo:: check text context, also check the optimization passes still do what they say
|
||||
#. :cmd:ref:`fsm_detect` 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.
|
||||
#. :cmd:ref:`fsm_extract` replaces the entire FSM (logic and state registers)
|
||||
with a ``$fsm`` cell.
|
||||
#. :cmd:ref:`fsm_opt` optimizes the FSM. Called multiple times.
|
||||
#. :cmd:ref:`fsm_expand` optionally merges additional auxilliary gates into the
|
||||
``$fsm`` cell.
|
||||
#. :cmd:ref:`fsm_recode` also optimizes the FSM.
|
||||
#. :cmd:ref:`fsm_info` logs internal FSM information.
|
||||
#. :cmd:ref:`fsm_export` optionally exports each FSM to KISS2 files.
|
||||
#. :cmd:ref:`fsm_map` converts the (optimized) ``$fsm`` cell back to logic and
|
||||
registers.
|
||||
|
||||
Yosys employs a number of optimizations to generate better and cleaner results.
|
||||
This chapter outlines these optimizations.
|
||||
|
||||
Simple optimizations
|
||||
--------------------
|
||||
|
||||
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 :cmd:ref:`opt`:
|
||||
|
||||
- ``opt_expr``
|
||||
- ``opt_merge -nomux``
|
||||
|
||||
- Repeat until result is stable:
|
||||
|
||||
- ``opt_muxtree``
|
||||
- ``opt_reduce``
|
||||
- ``opt_merge``
|
||||
- ``opt_rmdff``
|
||||
- ``opt_clean``
|
||||
- ``opt_expr``
|
||||
|
||||
The following section describes each of the ``opt_`` passes.
|
||||
|
||||
The :cmd:ref:`opt_expr` pass
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
This pass performs const folding on the internal combinational cell types
|
||||
described in :doc:`/yosys_internals/formats/cell_library`. 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 ``$_AND_`` cells as used in :cmd:ref:`opt_expr`.
|
||||
:name: tab:opt_expr_and
|
||||
:align: center
|
||||
|
||||
========= ========= ===========
|
||||
A-Input B-Input Replacement
|
||||
========= ========= ===========
|
||||
any 0 0
|
||||
0 any 0
|
||||
1 1 1
|
||||
--------- --------- -----------
|
||||
X/Z X/Z X
|
||||
1 X/Z X
|
||||
X/Z 1 X
|
||||
--------- --------- -----------
|
||||
any X/Z 0
|
||||
X/Z any 0
|
||||
--------- --------- -----------
|
||||
:math:`a` 1 :math:`a`
|
||||
1 :math:`b` :math:`b`
|
||||
========= ========= ===========
|
||||
|
||||
.. todo:: How to format table?
|
||||
|
||||
:numref:`Table %s <tab:opt_expr_and>` shows the replacement rules used for
|
||||
optimizing an ``$_AND_`` gate. The first three rules implement the obvious const
|
||||
folding rules. Note that 'any' might include dynamic values calculated by other
|
||||
parts of the circuit. The following three lines propagate undef (X) states.
|
||||
These are the only three cases in which it is allowed to propagate an undef
|
||||
according to Sec. 5.1.10 of IEEE Std. 1364-2005 :cite:p:`Verilog2005`.
|
||||
|
||||
The next two lines assume the value 0 for undef states. These two rules are only
|
||||
used if no other substitutions are possible in the current module. If other
|
||||
substitutions are possible they are performed first, in the hope that the 'any'
|
||||
will change to an undef value or a 1 and therefore the output can be set to
|
||||
undef.
|
||||
|
||||
The last two lines simply replace an ``$_AND_`` gate with one constant-1 input
|
||||
with a buffer.
|
||||
|
||||
Besides this basic const folding the :cmd:ref:`opt_expr` pass can replace 1-bit
|
||||
wide ``$eq`` and ``$ne`` cells with buffers or not-gates if one input is
|
||||
constant.
|
||||
|
||||
The :cmd:ref:`opt_expr` pass is very conservative regarding optimizing ``$mux``
|
||||
cells, as these cells are often used to model decision-trees and breaking these
|
||||
trees can interfere with other optimizations.
|
||||
|
||||
The :cmd:ref:`opt_muxtree` pass
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
This pass optimizes trees of multiplexer cells by analyzing the select inputs.
|
||||
Consider the following simple example:
|
||||
|
||||
.. code:: verilog
|
||||
|
||||
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 :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 :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
|
||||
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 ``$reduce_or``
|
||||
cell that combines the original select bits.
|
||||
|
||||
Lastly this pass consolidates trees of ``$reduce_and`` cells and trees of
|
||||
``$reduce_or`` cells to single large ``$reduce_and`` or ``$reduce_or`` cells.
|
||||
|
||||
These three simple optimizations are performed in a loop until a stable result
|
||||
is produced.
|
||||
|
||||
The ``opt_rmdff`` pass
|
||||
~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
.. todo:: Update to ``opt_dff``
|
||||
|
||||
This pass identifies single-bit d-type flip-flops (``$_DFF_``, ``$dff``, and
|
||||
``$adff`` cells) with a constant data input and replaces them with a constant
|
||||
driver.
|
||||
|
||||
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 :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
|
||||
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 :cmd:ref:`opt_muxtree` to identify
|
||||
possible optimizations.
|
||||
|
||||
FSM extraction and encoding
|
||||
---------------------------
|
||||
See also :doc:`/cmd/fsm`.
|
||||
|
||||
The fsm pass performs finite-state-machine (FSM) extraction and recoding. The
|
||||
fsm pass simply executes the following other passes:
|
||||
|
|
@ -328,14 +194,4 @@ 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 .
|
||||
|
||||
Logic optimization
|
||||
------------------
|
||||
|
||||
Yosys can perform multi-level combinational logic optimization on gate-level
|
||||
netlists using the external program ABC . The abc pass extracts the
|
||||
combinational gate-level parts of the design, passes it through ABC, and
|
||||
re-integrates the results. The abc pass can also be used to perform other
|
||||
operations using ABC, such as technology mapping (see :ref:`sec:techmap_extern`
|
||||
for details).
|
||||
Formality.
|
||||
|
|
@ -5,6 +5,9 @@ Synthesis in detail
|
|||
:maxdepth: 3
|
||||
|
||||
synth
|
||||
opt_passes
|
||||
proc
|
||||
memory_mapping
|
||||
fsm
|
||||
memory
|
||||
opt
|
||||
abc
|
||||
|
||||
|
|
|
|||
|
|
@ -1,20 +1,88 @@
|
|||
.. _chapter:memorymap:
|
||||
Memory handling
|
||||
===============
|
||||
|
||||
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 :cmd:ref:`memory`
|
||||
pass transforms memories to an implementation. Per default that is logic for
|
||||
address decoders and registers. It also is a macro command that the other common
|
||||
``memory_*`` commands in a sensible order:
|
||||
|
||||
.. todo:: fill out missing :cmd:ref:`memory` subcommands descriptions
|
||||
|
||||
#. :cmd:ref:`memory_bmux2rom`
|
||||
#. :cmd:ref:`memory_dff` merges registers into the memory read- and write cells.
|
||||
#. :cmd:ref:`memory_share`
|
||||
#. :cmd:ref:`memory_memx`
|
||||
#. :cmd:ref:`memory_collect` collects all read and write cells for a memory and
|
||||
transforms them into one multi-port memory cell.
|
||||
#. :cmd:ref:`memory_bram`
|
||||
#. :cmd:ref:`memory_map` takes the multi-port memory cell and transforms it to
|
||||
address decoder logic and registers.
|
||||
|
||||
For more information about :cmd:ref:`memory`, such as disabling certain sub
|
||||
commands, see :doc:`/cmd/memory`.
|
||||
|
||||
Example
|
||||
-------
|
||||
|
||||
.. todo:: describe ``memory`` images
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/memory_01.*
|
||||
:class: width-helper
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/memory_01.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/memory_01.ys``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/memory_01.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/memory_01.v``
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/memory_02.*
|
||||
:class: width-helper
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/memory_02.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/memory_02.v``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/memory_02.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/memory_02.ys``
|
||||
|
||||
.. _memory_map:
|
||||
|
||||
Memory mapping
|
||||
==============
|
||||
^^^^^^^^^^^^^^
|
||||
|
||||
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.
|
||||
.. todo:: :cmd:ref:`memory_libmap` description
|
||||
|
||||
Usually it is preferred to use architecture-specific RAM resources for memory.
|
||||
For example:
|
||||
|
||||
.. code-block:: yoscrypt
|
||||
|
||||
memory -nomap
|
||||
memory_libmap -lib my_memory_map.txt
|
||||
techmap -map my_memory_map.v
|
||||
memory_map
|
||||
|
||||
Supported memory patterns
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
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, `wbe`_ 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>`_
|
||||
|
||||
Additional notes
|
||||
----------------
|
||||
Notes
|
||||
-----
|
||||
|
||||
Memory kind selection
|
||||
~~~~~~~~~~~~~~~~~~~~~
|
||||
|
|
@ -95,7 +163,9 @@ 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 `Synchronous read port with initial value`_.
|
||||
tasks. For an example pattern, see `sr_init`_.
|
||||
|
||||
.. _wbe:
|
||||
|
||||
Write port with byte enables
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
|
@ -128,6 +198,8 @@ Write port with byte enables
|
|||
Simple dual port (SDP) memory patterns
|
||||
--------------------------------------
|
||||
|
||||
.. todo:: assorted enables, e.g. cen, wen+ren
|
||||
|
||||
Asynchronous-read SDP
|
||||
~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
|
|
@ -219,6 +291,8 @@ Synchronous SDP with undefined collision behavior
|
|||
read_data <= mem[read_addr];
|
||||
end
|
||||
|
||||
.. _sdp_wf:
|
||||
|
||||
Synchronous SDP with write-first behavior
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
|
|
@ -335,6 +409,8 @@ Synchronous single-port RAM with write-first behavior
|
|||
read_data <= mem[addr];
|
||||
end
|
||||
|
||||
.. _sr_init:
|
||||
|
||||
Synchronous read port with initial value
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
|
|
@ -436,6 +512,8 @@ Asymmetric memory is supported on all targets, but may require emulation circuit
|
|||
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:
|
||||
|
||||
Wide synchronous read port
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
|
|
@ -597,7 +675,7 @@ Patterns only supported with Verific
|
|||
Synchronous SDP with write-first behavior via blocking assignments
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
- Use `Synchronous SDP with write-first behavior`_ for compatibility with Yosys
|
||||
- Use `sdp_wf`_ for compatibility with Yosys
|
||||
Verilog frontend.
|
||||
|
||||
.. code:: verilog
|
||||
|
|
@ -615,8 +693,8 @@ Synchronous SDP with write-first behavior via blocking assignments
|
|||
Asymmetric memories via part selection
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
- Build wide ports out of narrow ports instead (see `Wide synchronous read
|
||||
port`_) for compatibility with Yosys Verilog frontend.
|
||||
- Build wide ports out of narrow ports instead (see `wide_sr`_) for
|
||||
compatibility with Yosys Verilog frontend.
|
||||
|
||||
.. code:: verilog
|
||||
|
||||
|
|
@ -0,0 +1,233 @@
|
|||
Optimization passes
|
||||
===================
|
||||
|
||||
.. todo:: check text context, also check the optimization passes still do what they say
|
||||
|
||||
Yosys employs a number of optimizations to generate better and cleaner results.
|
||||
This chapter outlines these optimizations.
|
||||
|
||||
The :cmd:ref:`opt` pass
|
||||
--------------------------
|
||||
|
||||
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:
|
||||
|
||||
.. code-block:: yoscrypt
|
||||
|
||||
opt_expr # const folding and simple expression rewriting
|
||||
opt_merge -nomux # merging identical cells
|
||||
|
||||
do
|
||||
opt_muxtree # remove never-active branches from multiplexer tree
|
||||
opt_reduce # consolidate trees of boolean ops to reduce functions
|
||||
opt_merge # merging identical cells
|
||||
opt_rmdff # remove/simplify registers with constant inputs
|
||||
opt_clean # remove unused objects (cells, wires) from design
|
||||
opt_expr # const folding and simple expression rewriting
|
||||
while [changed design]
|
||||
|
||||
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
|
||||
|
||||
hierarchy; proc; opt; memory; opt_expr;; fsm;;
|
||||
|
||||
The :cmd:ref:`opt_expr` pass
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
This pass performs const folding on the internal combinational cell types
|
||||
described in :doc:`/yosys_internals/formats/cell_library`. 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 ``$_AND_`` cells as used in :cmd:ref:`opt_expr`.
|
||||
:name: tab:opt_expr_and
|
||||
:align: center
|
||||
|
||||
========= ========= ===========
|
||||
A-Input B-Input Replacement
|
||||
========= ========= ===========
|
||||
any 0 0
|
||||
0 any 0
|
||||
1 1 1
|
||||
--------- --------- -----------
|
||||
X/Z X/Z X
|
||||
1 X/Z X
|
||||
X/Z 1 X
|
||||
--------- --------- -----------
|
||||
any X/Z 0
|
||||
X/Z any 0
|
||||
--------- --------- -----------
|
||||
:math:`a` 1 :math:`a`
|
||||
1 :math:`b` :math:`b`
|
||||
========= ========= ===========
|
||||
|
||||
.. todo:: How to format table?
|
||||
|
||||
:numref:`Table %s <tab:opt_expr_and>` shows the replacement rules used for
|
||||
optimizing an ``$_AND_`` gate. The first three rules implement the obvious const
|
||||
folding rules. Note that 'any' might include dynamic values calculated by other
|
||||
parts of the circuit. The following three lines propagate undef (X) states.
|
||||
These are the only three cases in which it is allowed to propagate an undef
|
||||
according to Sec. 5.1.10 of IEEE Std. 1364-2005 :cite:p:`Verilog2005`.
|
||||
|
||||
The next two lines assume the value 0 for undef states. These two rules are only
|
||||
used if no other substitutions are possible in the current module. If other
|
||||
substitutions are possible they are performed first, in the hope that the 'any'
|
||||
will change to an undef value or a 1 and therefore the output can be set to
|
||||
undef.
|
||||
|
||||
The last two lines simply replace an ``$_AND_`` gate with one constant-1 input
|
||||
with a buffer.
|
||||
|
||||
Besides this basic const folding the :cmd:ref:`opt_expr` pass can replace 1-bit
|
||||
wide ``$eq`` and ``$ne`` cells with buffers or not-gates if one input is
|
||||
constant.
|
||||
|
||||
The :cmd:ref:`opt_expr` pass is very conservative regarding optimizing ``$mux``
|
||||
cells, as these cells are often used to model decision-trees and breaking these
|
||||
trees can interfere with other optimizations.
|
||||
|
||||
The :cmd:ref:`opt_muxtree` pass
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
This pass optimizes trees of multiplexer cells by analyzing the select inputs.
|
||||
Consider the following simple example:
|
||||
|
||||
.. code:: verilog
|
||||
|
||||
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 :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 :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
|
||||
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 ``$reduce_or``
|
||||
cell that combines the original select bits.
|
||||
|
||||
Lastly this pass consolidates trees of ``$reduce_and`` cells and trees of
|
||||
``$reduce_or`` cells to single large ``$reduce_and`` or ``$reduce_or`` cells.
|
||||
|
||||
These three simple optimizations are performed in a loop until a stable result
|
||||
is produced.
|
||||
|
||||
The ``opt_rmdff`` pass
|
||||
~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
.. todo:: Update to ``opt_dff``
|
||||
|
||||
This pass identifies single-bit d-type flip-flops (``$_DFF_``, ``$dff``, and
|
||||
``$adff`` cells) with a constant data input and replaces them with a constant
|
||||
driver.
|
||||
|
||||
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 :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
|
||||
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 :cmd:ref:`opt_muxtree` to identify
|
||||
possible optimizations.
|
||||
|
||||
Example
|
||||
~~~~~~~
|
||||
|
||||
.. todo:: describe ``opt`` images
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/opt_01.*
|
||||
:class: width-helper
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/opt_01.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/opt_01.ys``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/opt_01.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/opt_01.v``
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/opt_02.*
|
||||
:class: width-helper
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/opt_02.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/opt_02.ys``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/opt_02.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/opt_02.v``
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/opt_03.*
|
||||
:class: width-helper
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/opt_03.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/opt_03.ys``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/opt_03.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/opt_03.v``
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/opt_04.*
|
||||
:class: width-helper
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/opt_04.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/opt_04.v``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/opt_04.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/opt_04.ys``
|
||||
|
||||
When to use :cmd:ref:`opt` or :cmd:ref:`clean`
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
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.
|
||||
|
||||
It is generally 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 these cases as the possible loss.
|
||||
|
||||
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.
|
||||
|
||||
Other optimizations
|
||||
-------------------
|
||||
|
||||
.. todo:: more on the other optimizations
|
||||
|
||||
- :doc:`/cmd/wreduce`
|
||||
- :doc:`/cmd/peepopt`
|
||||
- :doc:`/cmd/share`
|
||||
- :cmd:ref:`abc` and :cmd:ref:`abc9`, see also: :doc:`abc`.
|
||||
|
|
@ -1,4 +1,67 @@
|
|||
The :cmd:ref:`proc` command
|
||||
---------------------------
|
||||
Converting process blocks
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
text
|
||||
The Verilog frontend converts ``always``-blocks to RTL netlists for the
|
||||
expressions and "processess" for the control- and memory elements. The
|
||||
:cmd:ref:`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:
|
||||
|
||||
#. :cmd:ref:`proc_clean` removes empty branches and processes.
|
||||
#. :cmd:ref:`proc_rmdead` removes unreachable branches.
|
||||
#. :cmd:ref:`proc_prune`
|
||||
#. :cmd:ref:`proc_init` special handling of "initial" blocks.
|
||||
#. :cmd:ref:`proc_arst` identifies modeling of async resets.
|
||||
#. :cmd:ref:`proc_rom`
|
||||
#. :cmd:ref:`proc_mux` converts decision trees to multiplexer networks.
|
||||
#. :cmd:ref:`proc_dlatch`
|
||||
#. :cmd:ref:`proc_dff` extracts registers from processes.
|
||||
#. :cmd:ref:`proc_memwr`
|
||||
#. :cmd:ref:`proc_clean` this should remove all the processes, provided all went
|
||||
fine.
|
||||
|
||||
After all the ``proc_*`` commands, :yoscrypt:`opt_expr` is called. This can be
|
||||
disabled by calling :yoscrypt:`proc -noopt`. For more information about
|
||||
:cmd:ref:`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 :cmd:ref:`proc` is the first command in the actual synthesis procedure
|
||||
after design elaboration.
|
||||
|
||||
Example
|
||||
^^^^^^^
|
||||
|
||||
.. todo:: describe ``proc`` images
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/proc_01.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/proc_01.v``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/proc_01.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/proc_01.ys``
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/proc_01.*
|
||||
:class: width-helper
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/proc_02.*
|
||||
:class: width-helper
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/proc_02.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/proc_02.v``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/proc_02.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/proc_02.ys``
|
||||
|
||||
.. figure:: /_images/code_examples/synth_flow/proc_03.*
|
||||
:class: width-helper
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/proc_03.ys
|
||||
:language: yoscrypt
|
||||
:caption: ``docs/source/code_examples/synth_flow/proc_03.ys``
|
||||
|
||||
.. literalinclude:: /code_examples/synth_flow/proc_03.v
|
||||
:language: verilog
|
||||
:caption: ``docs/source/code_examples/synth_flow/proc_03.v``
|
||||
|
|
|
|||
|
|
@ -1,15 +1,5 @@
|
|||
Introduction to synthesis
|
||||
-------------------------
|
||||
|
||||
The generic ``synth``
|
||||
~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
The following commands are executed by the :cmd:ref:`synth` command:
|
||||
|
||||
.. literalinclude:: /cmd/synth.rst
|
||||
:start-at: begin:
|
||||
:end-before: .. raw:: latex
|
||||
:dedent:
|
||||
Synth commands
|
||||
--------------
|
||||
|
||||
Packaged ``synth_*`` commands
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
|
@ -38,3 +28,20 @@ being targeted.
|
|||
- :doc:`/cmd/synth_quicklogic`
|
||||
- :doc:`/cmd/synth_sf2`
|
||||
- :doc:`/cmd/synth_xilinx`
|
||||
|
||||
General synthesis
|
||||
~~~~~~~~~~~~~~~~~
|
||||
|
||||
In addition to the above hardware-specific synth commands, there is also
|
||||
:doc:`/cmd/prep`. This command is limited to coarse-grain synthesis, without
|
||||
getting into any architecture-specific mappings or optimizations. Among other
|
||||
things, this is useful for design verification.
|
||||
|
||||
The following commands are executed by the :cmd:ref:`prep` command:
|
||||
|
||||
.. literalinclude:: /cmd/prep.rst
|
||||
:start-at: begin:
|
||||
:end-before: .. raw:: latex
|
||||
:dedent:
|
||||
|
||||
The following sections will get more into what each of these commands do.
|
||||
|
|
|
|||
Loading…
Reference in New Issue