diff options
Diffstat (limited to 'nexus/pack.cc')
| -rw-r--r-- | nexus/pack.cc | 29 |
1 files changed, 15 insertions, 14 deletions
diff --git a/nexus/pack.cc b/nexus/pack.cc index be298ef0..8200f845 100644 --- a/nexus/pack.cc +++ b/nexus/pack.cc @@ -2307,6 +2307,11 @@ struct NexusPacker 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"); + } + size_t num_comb = 0; size_t num_ff = 0; size_t num_pair = 0; @@ -2338,7 +2343,6 @@ struct NexusPacker continue; } if (di->driver.port != id_F && - di->driver.port != id_F1 && di->driver.port != id_OFX) { continue; @@ -2377,27 +2381,24 @@ struct NexusPacker // Attach the FF to the existing cluster of the LUT else { - // Find the cluster root - CellInfo* root = nullptr; - if (!lut->constr_children.empty()) { - root = lut; - } - else { - for (auto &it : ctx->cells) { - if (it.second->cluster == lut->cluster && !it.second->constr_children.empty()) { - root = it.second.get(); - break; - } + // 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; } } - NPNR_ASSERT(root != nullptr); + + // 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 = false; + ff->constr_abs_z = lut->constr_abs_z; root->constr_children.push_back(ff); num_glue++; |