mirrors/yosys
3
0
Fork 0
mirror of https://github.com/YosysHQ/yosys synced 2025-04-23 09:05:32 +00:00
Code Activity

dfflegalize: Add special support for const-D latches.

Browse source 
Those can be created by `opt_dff` when optimizing `$adff` with const
clock, or with D == Q.  Make dfflegalize do the opposite transform
when such dlatches would be otherwise unimplementable.
This commit is contained in:
Marcelina Kościelnicka 2020-07-06 22:52:05 +02:00
parent 000fd08198
commit e9c2c1b717
2 changed files with 71 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

18
passes/techmap/dfflegalize.cc
View file

@ -659,6 +659,24 @@ flip_dqisr:;
// This init value is not supported at all...
if (supported_dlatch & flip_initmask(initmask))
goto flip_dqi;
if ((sig_d == State::S0 && (supported_adff0 & initmask)) ||
(sig_d == State::S1 && (supported_adff1 & initmask)) ||
(sig_d == State::S0 && (supported_adff1 & flip_initmask(initmask))) ||
(sig_d == State::S1 && (supported_adff0 & flip_initmask(initmask)))
) {
// Special case: const-D dlatch can be converted into adff with const clock.
ff_type = (sig_d == State::S0) ? FF_ADFF0 : FF_ADFF1;
if (ff_neg & NEG_E) {
ff_neg &= ~NEG_E;
ff_neg |= NEG_R;
}
sig_r = sig_e;
sig_d = State::Sx;
sig_c = State::S1;
continue;
}
if (!supported_dlatch)
reason = "dlatch are not supported";
else