The new bitwise case equality (`$bweqx`) and bitwise mux (`$bwmux`)
cells enable compact encoding and decoding of 3-valued logic signals
using multiple 2-valued signals.
The previous approach only initialized past_d and past_ad while for FST
cosim we also need to initialize the other past values like past_clk,
etc. Also to properly initialize them, we need to run a combinational
update step in case any of the wires feeding into the FF are private or
otherwise not part of the FST.
Otherwise the final values will not show up in gtkwave waveforms
when looking at the generated traces.
Signed-off-by: Claire Xenia Wolf <claire@clairexen.net>
* Change simlib's $mux cell to use the ternary operator as $_MUX_
already does
* Stop opt_expr -keepdc from changing S=x to S=0
* Change const eval of $mux and $pmux to match the updated simlib
(fixes sim)
* The sat behavior of $mux already matches the updated simlib
The verilog frontend uses $mux for the ternary operators and this
changes all interpreations of the $mux cell (that I found) to match the
verilog simulation behavior for the ternary operator. For 'if' and
'case' expressions the frontend may also use $mux but uses $eqx if the
verilog simulation behavior is requested with the '-ifx' option.
For $pmux there is a remaining mismatch between the sat behavior and the
simlib behavior. Resolving this requires more discussion, as the $pmux
cell does not directly correspond to a specific verilog construct.
This reverts commit 08be796cb8, reversing
changes made to 38dbb44fa0.
This fixes#2728. PR #641 did not actually "fix" #639.
The actual issue in #639 is not equiv_make, but assumptions in equiv_simple
that are not true for the test case provided in #639.
This is a complete rewrite of the FF replacing code.
The previous implementation tried to implement the negative hold time by
wrapping async control signals individually with pulse stretching. This
did not correctly model the interaction between different simultaneously
changing inputs (e.g. a falling ALOAD together with a changing AD would
load the changed AD instead of the value AD had when ALOAD was high; a
falling CLR could mask a raising SET for one cycle; etc.).
The new approach first has the logic for all updates using only sampled
values followed by the logic for all updates using only current values.
That way, e.g., a falling ALOAD will load the sampled AD value but a
still active ALOAD will load the current AD value.
The new code also has deterministic behavior for the initial state: no
operation is active when that operation would depend on a specific
previous signal value. This also means clk2fflogic will no longer
generate any additional uninitialized FFs.
I also documented the negative hold time behavior in the help message,
copying the relevant part from async2sync's help messages.
In 2fcc1ee72e, the following is apparantly added in order to mark any
number of undefined LUT inputs:
lut_a.append(RTLIL::Const(State::Sx, minlut - input_nodes.size()));
However this can only be done if the number of input nodes is less
than minlut.
This fixes#3317
After speaking with the author of ABC he let me know that ifraig is a very old command, and that &get; &fraig -x; &put is over 100x faster than ifraig with improved PPA results.
After making the change I confirmed that this is in fact a major speed up. On our internal designs in O(millions) of standard cells we saw multi hour reductions in runtime.
Also included is an improvement to the dress command. Using AIG based transformations removes the spec it SATs against. Proving the input blif will make sure that no matter what commands are run the dress command can still do its job. I noticed a regression against some LUT mapping jobs that prompted me to fix this.
Uses the regex below to search (using vscode):
^\t\tlog\("(.{10,}(?<!\\n)|.{81,}\\n)"\);
Finds any log messages double indented (which help messages are)
and checks if *either* there are is no newline character at the end,
*or* the number of characters before the newline is more than 80.
Verific generates a lot of FFs with an unused async load and we cannot
always optimize that away before running clk2fflogic, so check for that
special case here.
Find FFs with undefined initialization values for which changing the
initialization does not change the observable behavior and initialize
them. For -ff2anyinit, this reduces the number of generated $anyinit
cells that drive wires with private names.
This attribute can be used by formal backends to indicate which clocks
were mapped to the global clock. Update the btor and smt2 backend which
already handle clock inputs to understand this attribute.
These can be used to protect undefined flip-flop initialization values
from optimizations that are not sound for formal verification and can
help mapping all solver-provided values in witness traces for flows that
use different backends simultaneously.
Claire Xenia Wolf
Jannis Harder
Miodrag Milanovic
N. Engelhardt
KrystalDelusion
Kamyar Mohajerani
Dag Lem
Ethan Mahintorabi
KrystalDelusion
Aki Van Ness