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Docs: opt_expr

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Krystine Sherwin 2024-01-17 08:32:14 +13:00
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docs/source/getting_started/example_synth.rst
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@ -155,13 +155,6 @@ the register uses an ``$adff`` cell. If we look at the terminal output we can
also see all of the different ``proc_*`` commands being called. We will look at
each of these in more detail in :doc:`/using_yosys/synthesis/proc`.
.. TODO:: intro ``opt_expr``
:doc:`/cmd/opt_expr`
- by default called at the end of :cmd:ref:`proc`
- can be disabled with ``-noopt``
- done here for... reasons?
Notice how in the top left of :ref:`addr_gen_proc` we have a floating wire,
generated from the initial assignment of 0 to the ``addr`` wire. However, this
initial assignment is not synthesizable, so this will need to be cleaned up
@ -176,15 +169,14 @@ at the same time by separating them with a colon: :yoscrypt:`opt_expr; clean`.
``addr_gen`` module after :yoscrypt:`opt_expr; clean`
You may also notice that the highlighted ``$eq`` cell input of ``255`` has been
converted to ``8'11111111``. Constant values are presented in the format
You may also notice that the highlighted ``$eq`` cell input of ``255`` has
changed to ``8'11111111``. Constant values are presented in the format
``<bit_width>'<bits>``, with 32-bit values instead using the decimal number.
This indicates that the constant input has been reduced from 32-bit wide to
8-bit wide. :cmd:ref:`opt_expr` performs simple expression rewriting and
constant folding, which we discuss in more detail in
:doc:`/using_yosys/synthesis/opt`.
.. TODO:: why doesn't the 32-bit value 1 get converted to 1'1?
8-bit wide. This is a side-effect of running :cmd:ref:`opt_expr`, which
performs constant folding and simple expression rewriting. For more on why
this happens, refer to :doc:`/using_yosys/synthesis/opt` and the :ref:`section
on opt_expr <adv_opt_expr>`.
.. note::