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Recognise asynchronous set/reset.

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This commit is contained in:
nella 2026-06-15 15:44:50 +02:00
parent 8869ce61dc
commit a5bdb29d7f
2 changed files with 177 additions and 18 deletions
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126
passes/proc/proc_dlatch.cc
View file

@ -201,6 +201,77 @@ struct proc_dlatch_db_t
sig[index] = State::Sx;
cell->setPort(ID::A, sig);
}
bool sibling_undef = true;
for (int i = 0; i < (is_bwmux ? 1 : GetSize(sig_s)); i++)
if (sig_b[i*width + index] != State::Sx)
sibling_undef = false;
if (!sibling_undef) {
if (!is_bwmux) {
for (int i = 0; i < GetSize(sig_s); i++)
n = make_inner(sig_s[i], State::S0, n);
} else {
n = make_inner(sig_s[index], State::S0, n);
}
}
children.insert(n);
}
for (int i = 0; i < (is_bwmux ? 1 : GetSize(sig_s)); i++) {
n = find_mux_feedback(sig_b[i*width + index], needle, set_undef);
if (n != false_node) {
if (set_undef && sig_b[i*width + index] == needle) {
SigSpec sig = cell->getPort(ID::B);
sig[i*width + index] = State::Sx;
cell->setPort(ID::B, sig);
}
bool sibling_undef = (sig_a[index] == State::Sx);
if (!is_bwmux)
for (int j = 0; j < GetSize(sig_s); j++)
if (j != i && sig_b[j*width + index] != State::Sx)
sibling_undef = false;
if (!sibling_undef)
n = make_inner(sig_s[is_bwmux ? index : i], State::S1, n);
children.insert(n);
}
}
if (children.empty())
return false_node;
return make_inner(children);
}
int find_mux_constant(SigBit haystack, State needle, bool set_undef)
{
if (sigusers[haystack] > 1)
set_undef = false;
if (haystack == SigBit(needle))
return true_node;
auto it = mux_drivers.find(haystack);
if (it == mux_drivers.end())
return false_node;
Cell *cell = it->second.first;
int index = it->second.second;
log_assert(cell->type.in(ID($mux), ID($pmux), ID($bwmux)));
bool is_bwmux = (cell->type == ID($bwmux));
SigSpec sig_a = sigmap(cell->getPort(ID::A));
SigSpec sig_b = sigmap(cell->getPort(ID::B));
SigSpec sig_s = sigmap(cell->getPort(ID::S));
int width = GetSize(sig_a);
pool<int> children;
int n = find_mux_constant(sig_a[index], needle, set_undef);
if (n != false_node) {
if (set_undef && sig_a[index] == SigBit(needle)) {
SigSpec sig = cell->getPort(ID::A);
sig[index] = State::Sx;
cell->setPort(ID::A, sig);
}
if (!is_bwmux) {
for (int i = 0; i < GetSize(sig_s); i++)
n = make_inner(sig_s[i], State::S0, n);
@ -211,9 +282,9 @@ struct proc_dlatch_db_t
}
for (int i = 0; i < (is_bwmux ? 1 : GetSize(sig_s)); i++) {
n = find_mux_feedback(sig_b[i*width + index], needle, set_undef);
n = find_mux_constant(sig_b[i*width + index], needle, set_undef);
if (n != false_node) {
if (set_undef && sig_b[i*width + index] == needle) {
if (set_undef && sig_b[i*width + index] == SigBit(needle)) {
SigSpec sig = cell->getPort(ID::B);
sig[i*width + index] = State::Sx;
cell->setPort(ID::B, sig);
@ -349,7 +420,7 @@ void proc_dlatch(proc_dlatch_db_t &db, RTLIL::Process *proc)
{
RTLIL::SigSig latches_bits, nolatches_bits;
dict<SigBit, SigBit> latches_out_in;
dict<SigBit, int> latches_hold;
dict<SigBit, int> latches_hold, latches_rst, latches_set;
std::string src = proc->get_src_attribute();
for (auto sr : proc->syncs)
@ -381,15 +452,31 @@ void proc_dlatch(proc_dlatch_db_t &db, RTLIL::Process *proc)
latches_out_in.sort();
for (auto &it : latches_out_in) {
int n = db.find_mux_feedback(it.second, it.first, true);
if (n == db.false_node) {
if (db.find_mux_feedback(it.second, it.first, false) == db.false_node) {
nolatches_bits.first.append(it.first);
nolatches_bits.second.append(it.second);
} else {
latches_bits.first.append(it.first);
latches_bits.second.append(it.second);
latches_hold[it.first] = n;
continue;
}
latches_bits.first.append(it.first);
latches_bits.second.append(it.second);
int nrst = db.find_mux_constant(it.second, State::S0, false);
int nset = db.find_mux_constant(it.second, State::S1, false);
bool has_rst = (nrst != db.false_node);
bool has_set = (nset != db.false_node);
if (has_rst && !has_set)
nrst = db.find_mux_constant(it.second, State::S0, true);
else if (has_set && !has_rst)
nset = db.find_mux_constant(it.second, State::S1, true);
else
nrst = nset = db.false_node;
int n = db.find_mux_feedback(it.second, it.first, true);
log_assert(n != db.false_node);
latches_hold[it.first] = n;
latches_rst[it.first] = nrst;
latches_set[it.first] = nset;
}
int offset = 0;
@ -423,20 +510,35 @@ void proc_dlatch(proc_dlatch_db_t &db, RTLIL::Process *proc)
while (offset < GetSize(latches_bits.first))
{
int width = 1;
int n = latches_hold[latches_bits.first[offset]];
Wire *w = latches_bits.first[offset].wire;
SigBit obit = latches_bits.first[offset];
int n = latches_hold[obit];
int nrst = latches_rst[obit];
int nset = latches_set[obit];
Wire *w = obit.wire;
if (w != nullptr)
{
while (offset+width < GetSize(latches_bits.first) &&
n == latches_hold[latches_bits.first[offset+width]] &&
nrst == latches_rst[latches_bits.first[offset+width]] &&
nset == latches_set[latches_bits.first[offset+width]] &&
w == latches_bits.first[offset+width].wire)
width++;
SigSpec lhs = latches_bits.first.extract(offset, width);
SigSpec rhs = latches_bits.second.extract(offset, width);
Cell *cell = db.module->addDlatch(NEW_ID, db.module->Not(NEW_ID, db.make_hold(n, src)), rhs, lhs);
SigBit en = db.module->Not(NEW_ID, db.make_hold(n, src));
bool has_rst = (nrst != db.false_node);
bool has_set = (nset != db.false_node);
Cell *cell;
if (has_rst)
cell = db.module->addAdlatch(NEW_ID, en, db.make_hold(nrst, src), rhs, lhs, RTLIL::Const(State::S0, width));
else if (has_set)
cell = db.module->addAdlatch(NEW_ID, en, db.make_hold(nset, src), rhs, lhs, RTLIL::Const(State::S1, width));
else
cell = db.module->addDlatch(NEW_ID, en, rhs, lhs);
cell->set_src_attribute(src);
db.generated_dlatches.insert(cell);

69
passes/techmap/dfflegalize.cc
View file

@ -370,10 +370,16 @@ struct DffLegalizePass : public Pass {
else
fail_ff(ff, "initialized dffs with async set and reset are not supported");
} else {
if (!supported_cells[FF_DLATCHSR])
fail_ff(ff, "dlatch with async set and reset are not supported");
else
fail_ff(ff, "initialized dlatch with async set and reset are not supported");
if (!supported_dlatch) {
if (!supported_cells[FF_DLATCHSR])
fail_ff(ff, "dlatch with async set and reset are not supported");
else
fail_ff(ff, "initialized dlatch with async set and reset are not supported");
}
if (ff.cell)
log_warning("Emulating async set + reset latch with a plain D latch and logic for %s.%s\n", ff.module->name.unescape(), ff.cell->name.unescape());
emulate_dlatch(ff);
return;
}
}
@ -449,6 +455,51 @@ struct DffLegalizePass : public Pass {
legalize_ff(ff_sel);
}
void emulate_dlatch(FfData &ff) {
// emulate adlatch or dlatchsr
log_assert(!ff.has_clk);
log_assert(ff.has_aload);
log_assert(ff.width == 1);
auto active_high = [&](SigBit sig, bool pol) -> SigBit {
if (pol)
return sig;
return ff.is_fine ? ff.module->NotGate(NEW_ID, sig) : ff.module->Not(NEW_ID, sig)[0];
};
auto do_mux = [&](SigBit a, SigBit b, SigBit s) -> SigBit {
return ff.is_fine ? ff.module->MuxGate(NEW_ID, a, b, s) : ff.module->Mux(NEW_ID, a, b, s)[0];
};
auto do_or = [&](SigBit a, SigBit b) -> SigBit {
return ff.is_fine ? ff.module->OrGate(NEW_ID, a, b) : ff.module->Or(NEW_ID, a, b)[0];
};
SigBit en = active_high(ff.sig_aload, ff.pol_aload);
SigBit d = ff.sig_ad;
if (ff.has_sr) {
SigBit set = active_high(ff.sig_set[0], ff.pol_set);
SigBit clr = active_high(ff.sig_clr[0], ff.pol_clr);
// clr > set > load > hold
d = do_mux(d, State::S1, set);
d = do_mux(d, State::S0, clr);
en = do_or(en, do_or(set, clr));
ff.has_sr = false;
}
if (ff.has_arst) {
SigBit arst = active_high(ff.sig_arst[0], ff.pol_arst);
d = do_mux(d, ff.val_arst[0], arst);
en = do_or(en, arst);
ff.has_arst = false;
}
ff.sig_ad = d;
ff.sig_aload = en;
ff.pol_aload = true;
legalize_dlatch(ff);
}
void legalize_dff(FfData &ff) {
if (!try_flip(ff, supported_dff)) {
if (!supported_dff)
@ -742,8 +793,14 @@ struct DffLegalizePass : public Pass {
void legalize_adlatch(FfData &ff) {
if (!try_flip(ff, supported_adlatch)) {
if (!supported_adlatch)
fail_ff(ff, "D latches with async set or reset are not supported");
if (!supported_adlatch) {
if (!supported_dlatch)
fail_ff(ff, "D latches with async set or reset are not supported");
if (ff.cell)
log_warning("Emulating async reset latch with a plain D latch and logic for %s.%s\n", ff.module->name.unescape(), ff.cell->name.unescape());
emulate_dlatch(ff);
return;
}
if (!(supported_dlatch & (INIT_0 | INIT_1)))
fail_ff(ff, "initialized D latches are not supported");