Merge pull request #863 from antmicro/pack_lutff
nexus: LUT and FF clustering
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gatecat
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fd2d4a8f99
@ -51,6 +51,8 @@ po::options_description NexusCommandHandler::getArchOptions()
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specific.add_options()("fasm", po::value<std::string>(), "fasm file to write");
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specific.add_options()("pdc", po::value<std::string>(), "physical constraints file");
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specific.add_options()("no-post-place-opt", "disable post-place repacking (debugging use only)");
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specific.add_options()("no-pack-lutff", "disable packing (clustering) LUTs and FFs together");
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specific.add_options()("carry-lutff-ratio", po::value<float>(), "ratio of FFs to be added to carry-chain LUT clusters");
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return specific;
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}
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@ -76,6 +78,15 @@ std::unique_ptr<Context> NexusCommandHandler::createContext(dict<std::string, Pr
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auto ctx = std::unique_ptr<Context>(new Context(chipArgs));
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if (vm.count("no-post-place-opt"))
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ctx->settings[ctx->id("no_post_place_opt")] = Property::State::S1;
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if (vm.count("no-pack-lutff"))
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ctx->settings[ctx->id("no_pack_lutff")] = Property::State::S1;
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if (vm.count("carry-lutff-ratio")) {
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float ratio = vm["carry-lutff-ratio"].as<float>();
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if (ratio < 0.0f || ratio > 1.0f) {
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log_error("Carry LUT+FF packing ration must be between 0.0 and 1.0");
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}
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ctx->settings[ctx->id("carry_lutff_ratio")] = ratio;
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}
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return ctx;
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}
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171
nexus/pack.cc
171
nexus/pack.cc
@ -2304,6 +2304,172 @@ struct NexusPacker
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}
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}
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FFControlSet gather_ff_settings(CellInfo* cell) {
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NPNR_ASSERT(cell->type == id_OXIDE_FF);
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FFControlSet ctrlset;
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ctrlset.async = str_or_default(cell->params, id_SRMODE, "LSR_OVER_CE") == "ASYNC";
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ctrlset.regddr_en = is_enabled(cell, id_REGDDR);
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ctrlset.gsr_en = is_enabled(cell, id_GSR);
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ctrlset.clkmux = ctx->id(str_or_default(cell->params, id_CLKMUX, "CLK")).index;
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ctrlset.cemux = ctx->id(str_or_default(cell->params, id_CEMUX, "CE")).index;
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ctrlset.lsrmux = ctx->id(str_or_default(cell->params, id_LSRMUX, "LSR")).index;
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ctrlset.clk = get_net_or_empty(cell, id_CLK);
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ctrlset.ce = get_net_or_empty(cell, id_CE);
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ctrlset.lsr = get_net_or_empty(cell, id_LSR);
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return ctrlset;
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}
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void pack_lutffs () {
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log_info("Inferring LUT+FF pairs...\n");
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float carry_ratio = 1.0f;
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if (ctx->settings.find(ctx->id("carry_lutff_ratio")) != ctx->settings.end()) {
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carry_ratio = ctx->setting<float>("carry_lutff_ratio");
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}
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// FF control settings/signals are slice-wide. The dict below is used
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// to track settings of FFs glued to clusters which may span more than
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// one slice (eg. carry-chains). For now it is assumed that all FFs
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// in one cluster share the same settings and control signals.
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dict<IdString, FFControlSet> cluster_ffinfo;
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size_t num_comb = 0;
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size_t num_ff = 0;
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size_t num_pair = 0;
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size_t num_glue = 0;
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for (auto &cell : ctx->cells) {
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CellInfo *ff = cell.second.get();
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if (ff->type != id_OXIDE_FF) {
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continue;
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}
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num_ff++;
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// Get input net
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// At the packing stage all inputs go to M
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NetInfo *di = get_net_or_empty(ff, id_M);
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if (di == nullptr || di->driver.cell == nullptr) {
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continue;
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}
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// Skip if there are multiple sinks on that net
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if (di->users.size() != 1) {
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continue;
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}
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// Check if the driver is a LUT and the direct connection is from F
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CellInfo* lut = di->driver.cell;
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if (lut->type != id_OXIDE_COMB) {
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continue;
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}
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if (di->driver.port != id_F &&
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di->driver.port != id_OFX)
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{
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continue;
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}
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// The FF must not use M and DI at the same time
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if (get_net_or_empty(ff, id_DI)) {
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continue;
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}
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// The LUT must be in LOGIC/CARRY mode
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if (str_or_default(lut->params, id_MODE, "LOGIC") != "LOGIC" &&
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str_or_default(lut->params, id_MODE, "LOGIC") != "CCU2") {
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continue;
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}
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// The FF cannot be in another cluster
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if (ff->cluster != ClusterId()) {
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continue;
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}
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// Get FF settings
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auto ffinfo = gather_ff_settings(ff);
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// A free LUT, create a new cluster
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if (lut->cluster == ClusterId()) {
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lut->cluster = lut->name;
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lut->constr_children.push_back(ff);
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ff->cluster = lut->name;
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ff->constr_x = 0;
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ff->constr_y = 0;
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ff->constr_z = 2;
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ff->constr_abs_z = false;
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num_pair++;
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}
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// Attach the FF to the existing cluster of the LUT
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else {
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// Check if the FF settings match those of others in this
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// cluster. If not then reject this FF.
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//
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// This is a greedy approach - the first attached FF will
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// enforce its settings on all following candidates. A better
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// approach would be to first form groups of matching FFs for
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// a cluster and then attach only the largest group to it.
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if (cluster_ffinfo.count(lut->cluster)) {
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if (ffinfo != cluster_ffinfo.at(lut->cluster)) {
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continue;
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}
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}
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// No order not to make too large carry clusters pack only the
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// given fraction of FFs there.
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if(str_or_default(lut->params, id_MODE, "LOGIC") == "CCU2") {
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float r = (float)(ctx->rng() % 1000) * 1e-3f;
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if (r > carry_ratio) {
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continue;
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}
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}
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// Get the cluster root
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CellInfo* root = ctx->cells.at(lut->cluster).get();
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// Constrain the FF relative to the LUT
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ff->cluster = root->cluster;
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ff->constr_x = lut->constr_x;
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ff->constr_y = lut->constr_y;
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ff->constr_z = lut->constr_z + 2;
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ff->constr_abs_z = lut->constr_abs_z;
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root->constr_children.push_back(ff);
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num_glue++;
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}
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// Reconnect M to DI
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rename_port(ctx, ff, id_M, id_DI);
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ff->params[id_SEL] = std::string("DL");
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// Store FF settings of the cluster
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if (!cluster_ffinfo.count(lut->cluster)) {
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cluster_ffinfo.emplace(lut->cluster, ffinfo);
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}
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}
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// Count OXIDE_COMB, OXIDE_FF are already counted
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for (auto &cell : ctx->cells) {
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CellInfo *ff = cell.second.get();
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if (ff->type == id_OXIDE_COMB) {
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num_comb++;
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}
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}
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// Print statistics
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log_info(" Created %zu LUT+FF pairs and extended %zu clusters using total %zu FFs and %zu LUTs\n",
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num_pair,
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num_glue,
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num_ff,
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num_comb
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);
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}
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explicit NexusPacker(Context *ctx) : ctx(ctx) {}
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void operator()()
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@ -2323,6 +2489,11 @@ struct NexusPacker
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pack_luts();
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pack_ip();
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handle_iologic();
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if (!bool_or_default(ctx->settings, ctx->id("no_pack_lutff"))) {
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pack_lutffs();
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}
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promote_globals();
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place_globals();
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generate_constraints();
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