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booth: Redo baseline architecture summation

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Redo the summation logic: strive for some degree of balance on the
generated Wallace tree, emit an `$add` cell for the final summation.
This commit is contained in:
Martin Povišer 2023-11-22 14:59:54 +01:00
parent beb5cb55a5
commit d6566eb344
1 changed files with 44 additions and 11 deletions
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55
passes/techmap/booth.cc
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@ -67,6 +67,7 @@ struct BoothPassWorker {
SigMap sigmap;
int booth_counter;
bool lowpower = false;
bool mapped_cpa = false;
BoothPassWorker(RTLIL::Module *module) : module(module), sigmap(module) { booth_counter = 0; }
@ -297,6 +298,36 @@ struct BoothPassWorker {
}
}
SigSig WallaceSum(int width, std::vector<SigSpec> summands)
{
for (auto &s : summands)
s.extend_u0(width);
while (summands.size() > 2) {
std::vector<SigSpec> new_summands;
int i;
for (i = 0; i < (int) summands.size() - 2; i += 3) {
SigSpec x = module->addWire(NEW_ID, width);
SigSpec y = module->addWire(NEW_ID, width);
BuildBitwiseFa(module, NEW_ID.str(), summands[i], summands[i + 1],
summands[i + 2], x, y);
new_summands.push_back(y);
new_summands.push_back({x.extract(0, width - 1), State::S0});
}
new_summands.insert(new_summands.begin(), summands.begin() + i, summands.end());
std::swap(summands, new_summands);
}
if (!summands.size())
return SigSig(SigSpec(width, State::S0), SigSpec(width, State::S0));
else if (summands.size() == 1)
return SigSig(summands[0], SigSpec(width, State::S0));
else
return SigSig(summands[0], summands[1]);
}
/*
Build Multiplier.
-------------------------
@ -365,19 +396,16 @@ struct BoothPassWorker {
// Later on yosys will clean up unused constants
// DebugDumpAlignPP(aligned_pp);
SigSpec s_vec;
SigSpec c_vec;
std::vector<std::vector<RTLIL::Cell *>> debug_csa_trees;
debug_csa_trees.resize(z_sz);
BuildCSATree(module, aligned_pp, s_vec, c_vec, debug_csa_trees);
SigSig wtree_sum = WallaceSum(z_sz, aligned_pp);
// Debug code: Dump out the csa trees
// DumpCSATrees(debug_csa_trees);
// Build the CPA to do the final accumulation.
BuildCPA(module, s_vec, c_vec, Z);
log_assert(wtree_sum.second[0] == State::S0);
if (mapped_cpa)
BuildCPA(module, wtree_sum.first, {State::S0, wtree_sum.second.extract_end(1)}, Z);
else
module->addAdd(NEW_ID, wtree_sum.first, {wtree_sum.second.extract_end(1), State::S0}, Z);
}
/*
@ -1130,10 +1158,14 @@ struct BoothPass : public Pass {
log_header(design, "Executing BOOTH pass (map to Booth multipliers).\n");
size_t argidx;
bool mapped_cpa = false;
bool lowpower = false;
for (argidx = 1; argidx < args.size(); argidx++) {
break;
if (args[argidx] == "-lowpower")
if (args[argidx] == "-mapped_cpa")
// Have an undocumented option which helps with multiplier
// verification using specialized tools (AMulet2 in particular)
mapped_cpa = true;
else if (args[argidx] == "-lowpower")
lowpower = true;
else
break;
@ -1145,6 +1177,7 @@ struct BoothPass : public Pass {
for (auto mod : design->selected_modules()) {
if (!mod->has_processes_warn()) {
BoothPassWorker worker(mod);
worker.mapped_cpa = mapped_cpa;
worker.lowpower = lowpower;
worker.run();
total += worker.booth_counter;