yosys/docs/source/using_yosys/synthesis/index.rst

Synthesis in detail
-------------------

Synthesis can generally be broken down into coarse-grain synthesis, and
fine-grain synthesis.  We saw this in :doc:`/getting_started/example_synth`
where a design was loaded and elaborated and then went through a series of
coarse-grain optimizations before being mapped to hard blocks and fine-grain
cells.  Most commands in Yosys will target either coarse-grain representation or
fine-grain representation, with only a select few compatible with both states.

Commands such as `proc`, `fsm`, and `memory` rely on the additional information
in the coarse-grain representation, along with a number of optimizations such as
`wreduce`, `share`, and `alumacc`.  `opt` provides optimizations which are
useful in both states, while `techmap` is used to convert coarse-grain cells to
the corresponding fine-grain representation.

Single-bit cells (logic gates, FFs) as well as LUTs, half-adders, and
full-adders make up the bulk of the fine-grain representation and are necessary
for commands such as `abc`\ /`abc9`, `simplemap`, `dfflegalize`, and
`memory_map`.

.. toctree::
   :maxdepth: 3

   synth
   proc
   fsm
   memory
   opt
   techmap_synth
   extract
   abc
   cell_libs