Docs: Fix word_logic.rst

It somehow got lost in the rebase.
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Krystine Sherwin 2024-10-15 11:46:21 +13:00
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commit bc77575c22
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3 changed files with 47 additions and 45 deletions

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@ -23,6 +23,7 @@ Simulation models for the RTL cells can be found in the file
/cell/word_mem
/cell/word_fsm
/cell/word_arith
/cell/word_logic
/cell/word_spec
/cell/word_formal
/cell/word_debug

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@ -3,9 +3,6 @@ Coarse arithmetics
.. todo:: Add information about `$alu`, `$fa`, and `$lcu` cells.
Multiply-accumulate
~~~~~~~~~~~~~~~~~~~
The `$macc` cell type represents a generalized multiply and accumulate
operation. The cell is purely combinational. It outputs the result of summing up
a sequence of products and other injected summands.
@ -47,48 +44,6 @@ CONFIG parameter carries the following information:
B is an array of concatenated 1-bit-wide unsigned integers to also be summed up.
Arbitrary logic functions
~~~~~~~~~~~~~~~~~~~~~~~~~
The `$lut` cell type implements a single-output LUT (lookup table). It
implements an arbitrary logic function with its ``\LUT`` parameter to map input
port ``\A`` to values of ``\Y`` output port values. In psuedocode: ``Y =
\LUT[A]``. ``\A`` has width set by parameter ``\WIDTH`` and ``\Y`` has a width
of 1. Every logic function with a single bit output has a unique `$lut`
representation.
The `$sop` cell type implements a sum-of-products expression, also known as
disjunctive normal form (DNF). It implements an arbitrary logic function. Its
structure mimics a programmable logic array (PLA). Output port ``\Y`` is the sum
of products of the bits of the input port ``\A`` as defined by parameter
``\TABLE``. ``\A`` is ``\WIDTH`` bits wide. The number of products in the sum is
set by parameter ``\DEPTH``, and each product has two bits for each input bit -
for the presence of the unnegated and negated version of said input bit in the
product. Therefore the ``\TABLE`` parameter holds ``2 * \WIDTH * \DEPTH`` bits.
For example:
Let ``\WIDTH`` be 3. We would like to represent ``\Y =~\A[0] + \A[1]~\A[2]``.
There are 2 products to be summed, so ``\DEPTH`` shall be 2.
.. code-block::
~A[2]-----+
A[2]----+|
~A[1]---+||
A[1]--+|||
~A[0]-+||||
A[0]+|||||
|||||| product formula
010000 ~\A[0]
001001 \A[1]~\A[2]
So the value of ``\TABLE`` will become ``010000001001``.
Any logic function with a single bit output can be represented with ``$sop`` but
may have variously minimized or ordered summands represented in the ``\TABLE``
values.
.. autocellgroup:: arith
:members:
:source:

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@ -0,0 +1,46 @@
Arbitrary logic functions
-------------------------
The `$lut` cell type implements a single-output LUT (lookup table). It
implements an arbitrary logic function with its ``\LUT`` parameter to map input
port ``\A`` to values of ``\Y`` output port values. In psuedocode: ``Y =
\LUT[A]``. ``\A`` has width set by parameter ``\WIDTH`` and ``\Y`` has a width
of 1. Every logic function with a single bit output has a unique `$lut`
representation.
The `$sop` cell type implements a sum-of-products expression, also known as
disjunctive normal form (DNF). It implements an arbitrary logic function. Its
structure mimics a programmable logic array (PLA). Output port ``\Y`` is the sum
of products of the bits of the input port ``\A`` as defined by parameter
``\TABLE``. ``\A`` is ``\WIDTH`` bits wide. The number of products in the sum is
set by parameter ``\DEPTH``, and each product has two bits for each input bit -
for the presence of the unnegated and negated version of said input bit in the
product. Therefore the ``\TABLE`` parameter holds ``2 * \WIDTH * \DEPTH`` bits.
For example:
Let ``\WIDTH`` be 3. We would like to represent ``\Y =~\A[0] + \A[1]~\A[2]``.
There are 2 products to be summed, so ``\DEPTH`` shall be 2.
.. code-block::
~A[2]-----+
A[2]----+|
~A[1]---+||
A[1]--+|||
~A[0]-+||||
A[0]+|||||
|||||| product formula
010000 ~\A[0]
001001 \A[1]~\A[2]
So the value of ``\TABLE`` will become ``010000001001``.
Any logic function with a single bit output can be represented with ``$sop`` but
may have variously minimized or ordered summands represented in the ``\TABLE``
values.
.. autocellgroup:: logic
:members:
:source:
:linenos: