diff options
Diffstat (limited to 'nexus/pack.cc')
| -rw-r--r-- | nexus/pack.cc | 171 |
1 files changed, 171 insertions, 0 deletions
diff --git a/nexus/pack.cc b/nexus/pack.cc index 281a7cf2..0c771e82 100644 --- a/nexus/pack.cc +++ b/nexus/pack.cc @@ -2304,6 +2304,172 @@ struct NexusPacker } } + FFControlSet gather_ff_settings(CellInfo* cell) { + NPNR_ASSERT(cell->type == id_OXIDE_FF); + + FFControlSet ctrlset; + ctrlset.async = str_or_default(cell->params, id_SRMODE, "LSR_OVER_CE") == "ASYNC"; + ctrlset.regddr_en = is_enabled(cell, id_REGDDR); + ctrlset.gsr_en = is_enabled(cell, id_GSR); + ctrlset.clkmux = ctx->id(str_or_default(cell->params, id_CLKMUX, "CLK")).index; + ctrlset.cemux = ctx->id(str_or_default(cell->params, id_CEMUX, "CE")).index; + ctrlset.lsrmux = ctx->id(str_or_default(cell->params, id_LSRMUX, "LSR")).index; + ctrlset.clk = get_net_or_empty(cell, id_CLK); + ctrlset.ce = get_net_or_empty(cell, id_CE); + ctrlset.lsr = get_net_or_empty(cell, id_LSR); + + return ctrlset; + } + + void pack_lutffs () { + log_info("Inferring LUT+FF pairs...\n"); + + float carry_ratio = 1.0f; + if (ctx->settings.find(ctx->id("carry_lutff_ratio")) != ctx->settings.end()) { + carry_ratio = ctx->setting<float>("carry_lutff_ratio"); + } + + // FF control settings/signals are slice-wide. The dict below is used + // to track settings of FFs glued to clusters which may span more than + // one slice (eg. carry-chains). For now it is assumed that all FFs + // in one cluster share the same settings and control signals. + dict<IdString, FFControlSet> cluster_ffinfo; + + size_t num_comb = 0; + size_t num_ff = 0; + size_t num_pair = 0; + size_t num_glue = 0; + + for (auto &cell : ctx->cells) { + CellInfo *ff = cell.second.get(); + if (ff->type != id_OXIDE_FF) { + continue; + } + + num_ff++; + + // Get input net + // At the packing stage all inputs go to M + NetInfo *di = get_net_or_empty(ff, id_M); + if (di == nullptr || di->driver.cell == nullptr) { + continue; + } + + // Skip if there are multiple sinks on that net + if (di->users.size() != 1) { + continue; + } + + // Check if the driver is a LUT and the direct connection is from F + CellInfo* lut = di->driver.cell; + if (lut->type != id_OXIDE_COMB) { + continue; + } + if (di->driver.port != id_F && + di->driver.port != id_OFX) + { + continue; + } + + // The FF must not use M and DI at the same time + if (get_net_or_empty(ff, id_DI)) { + continue; + } + + // The LUT must be in LOGIC/CARRY mode + if (str_or_default(lut->params, id_MODE, "LOGIC") != "LOGIC" && + str_or_default(lut->params, id_MODE, "LOGIC") != "CCU2") { + continue; + } + + // The FF cannot be in another cluster + if (ff->cluster != ClusterId()) { + continue; + } + + // Get FF settings + auto ffinfo = gather_ff_settings(ff); + + // A free LUT, create a new cluster + if (lut->cluster == ClusterId()) { + + lut->cluster = lut->name; + lut->constr_children.push_back(ff); + + ff->cluster = lut->name; + ff->constr_x = 0; + ff->constr_y = 0; + ff->constr_z = 2; + ff->constr_abs_z = false; + + num_pair++; + } + // Attach the FF to the existing cluster of the LUT + else { + + // Check if the FF settings match those of others in this + // cluster. If not then reject this FF. + // + // This is a greedy approach - the first attached FF will + // enforce its settings on all following candidates. A better + // approach would be to first form groups of matching FFs for + // a cluster and then attach only the largest group to it. + if (cluster_ffinfo.count(lut->cluster)) { + if (ffinfo != cluster_ffinfo.at(lut->cluster)) { + continue; + } + } + + // No order not to make too large carry clusters pack only the + // given fraction of FFs there. + if(str_or_default(lut->params, id_MODE, "LOGIC") == "CCU2") { + float r = (float)(ctx->rng() % 1000) * 1e-3f; + if (r > carry_ratio) { + continue; + } + } + + // Get the cluster root + CellInfo* root = ctx->cells.at(lut->cluster).get(); + + // Constrain the FF relative to the LUT + ff->cluster = root->cluster; + ff->constr_x = lut->constr_x; + ff->constr_y = lut->constr_y; + ff->constr_z = lut->constr_z + 2; + ff->constr_abs_z = lut->constr_abs_z; + root->constr_children.push_back(ff); + + num_glue++; + } + + // Reconnect M to DI + rename_port(ctx, ff, id_M, id_DI); + ff->params[id_SEL] = std::string("DL"); + + // Store FF settings of the cluster + if (!cluster_ffinfo.count(lut->cluster)) { + cluster_ffinfo.emplace(lut->cluster, ffinfo); + } + } + + // Count OXIDE_COMB, OXIDE_FF are already counted + for (auto &cell : ctx->cells) { + CellInfo *ff = cell.second.get(); + if (ff->type == id_OXIDE_COMB) { + num_comb++; + } + } + + // Print statistics + log_info(" Created %zu LUT+FF pairs and extended %zu clusters using total %zu FFs and %zu LUTs\n", + num_pair, + num_glue, + num_ff, + num_comb + ); + } + explicit NexusPacker(Context *ctx) : ctx(ctx) {} void operator()() @@ -2323,6 +2489,11 @@ struct NexusPacker pack_luts(); pack_ip(); handle_iologic(); + + if (!bool_or_default(ctx->settings, ctx->id("no_pack_lutff"))) { + pack_lutffs(); + } + promote_globals(); place_globals(); generate_constraints(); |