From 6d154cfa1300cf88c1556657b37f7fbcc8da8d6a Mon Sep 17 00:00:00 2001 From: David Shah Date: Mon, 25 Jun 2018 15:39:46 +0200 Subject: ice40: Creating a carry chain splitter function Signed-off-by: David Shah --- common/nextpnr.h | 6 ++-- ice40/pack.cc | 12 ++++---- ice40/place_legaliser.cc | 78 ++++++++++++++++++++++++++++++++++++++++++------ 3 files changed, 77 insertions(+), 19 deletions(-) diff --git a/common/nextpnr.h b/common/nextpnr.h index df9d7e3e..71a52758 100644 --- a/common/nextpnr.h +++ b/common/nextpnr.h @@ -207,13 +207,13 @@ struct BaseCtx IdString::initialize_add(this, "", 0); IdString::initialize_arch(this); } - + ~BaseCtx() { - for(auto &item : nets) { + for (auto &item : nets) { delete item.second; } - for(auto &item : cells) { + for (auto &item : cells) { delete item.second; } delete idstring_str_to_idx; diff --git a/ice40/pack.cc b/ice40/pack.cc index 85c1af8c..54e6dad2 100644 --- a/ice40/pack.cc +++ b/ice40/pack.cc @@ -258,7 +258,7 @@ static void pack_constants(Context *ctx) std::vector dead_nets; - bool gnd_used = false, vcc_used = false; + bool gnd_used = false; for (auto net : sorted(ctx->nets)) { NetInfo *ni = net.second; @@ -268,7 +268,6 @@ static void pack_constants(Context *ctx) dead_nets.push_back(net.first); } else if (ni->driver.cell != nullptr && ni->driver.cell->type == ctx->id("VCC")) { set_net_constant(ctx, ni, vcc_net, true); - vcc_used = true; dead_nets.push_back(net.first); } } @@ -277,11 +276,10 @@ static void pack_constants(Context *ctx) ctx->cells[gnd_cell->name] = gnd_cell; ctx->nets[gnd_net->name] = gnd_net; } - - if (vcc_used) { - ctx->cells[vcc_cell->name] = vcc_cell; - ctx->nets[vcc_net->name] = vcc_net; - } + // Vcc cell always inserted for now, as it may be needed during carry legalisation (TODO: trim later if actually + // never used?) + ctx->cells[vcc_cell->name] = vcc_cell; + ctx->nets[vcc_net->name] = vcc_net; for (auto dn : dead_nets) ctx->nets.erase(dn); diff --git a/ice40/place_legaliser.cc b/ice40/place_legaliser.cc index a4e8da0c..0372ad6c 100644 --- a/ice40/place_legaliser.cc +++ b/ice40/place_legaliser.cc @@ -27,13 +27,18 @@ NEXTPNR_NAMESPACE_BEGIN +struct CellChain +{ + std::vector cells; +}; + // Generic chain finder template -std::vector> find_chains(const Context *ctx, F1 cell_type_predicate, F2 get_previous, - F3 get_next, size_t min_length = 2) +std::vector find_chains(const Context *ctx, F1 cell_type_predicate, F2 get_previous, F3 get_next, + size_t min_length = 2) { std::set chained; - std::vector> chains; + std::vector chains; for (auto cell : sorted(ctx->cells)) { if (chained.find(cell.first) != chained.end()) continue; @@ -45,15 +50,15 @@ std::vector> find_chains(const Context *ctx, F1 cell_typ start = prev_start; prev_start = get_previous(ctx, start); } - std::vector chain; + CellChain chain; CellInfo *end = start; while (end != nullptr) { - chain.push_back(end); + chain.cells.push_back(end); end = get_next(ctx, end); } - if (chain.size() >= min_length) { + if (chain.cells.size() >= min_length) { chains.push_back(chain); - for (auto c : chain) + for (auto c : chain.cells) chained.insert(c->name); } } @@ -95,7 +100,7 @@ class PlacementLegaliser private: bool legalise_carries() { - std::vector> carry_chains = find_chains( + std::vector carry_chains = find_chains( ctx, is_lc, [](const Context *ctx, const CellInfo *cell) { return net_driven_by(ctx, cell->ports.at(ctx->id("CIN")).net, is_lc, ctx->id("COUT")); @@ -103,15 +108,63 @@ class PlacementLegaliser [](const Context *ctx, const CellInfo *cell) { return net_only_drives(ctx, cell->ports.at(ctx->id("COUT")).net, is_lc, ctx->id("CIN"), false); }); - // TODO + for (auto chain : carry_chains) { + } return true; } + // Split a carry chain into multiple legal chains + std::vector split_carry_chain(Context *ctx, CellChain &carryc) + { + bool start_of_chain = true; + std::vector chains; + std::vector tile; + const int max_length = (ctx->chip_info->height - 2) * 8 - 2; + auto curr_cell = carryc.cells.begin(); + while (curr_cell != carryc.cells.end()) { + CellInfo *cell = *curr_cell; + if (tile.size() >= 8) { + tile.clear(); + } + if (start_of_chain) { + tile.clear(); + chains.emplace_back(); + start_of_chain = false; + if (cell->ports.at(ctx->id("CIN")).net) { + // CIN is not constant and not part of a chain. Must feed in from fabric + CellInfo *feedin = make_carry_feed_in(cell, cell->ports.at(ctx->id("CIN"))); + chains.back().cells.push_back(feedin); + tile.push_back(feedin); + } + } + tile.push_back(cell); + chains.back().cells.push_back(cell); + bool split_chain = (!ctx->logicCellsCompatible(tile)) || (int(chains.back().cells.size()) > max_length); + if (split_chain) { + CellInfo *passout = make_carry_pass_out(cell->ports.at(ctx->id("COUT"))); + tile.pop_back(); + chains.back().cells.back() = passout; + start_of_chain = true; + } else { + NetInfo *carry_net = cell->ports.at(ctx->id("COUT")).net; + if (carry_net != nullptr && carry_net->users.size() > 1) { + CellInfo *passout = make_carry_pass_out(cell->ports.at(ctx->id("COUT"))); + chains.back().cells.push_back(passout); + tile.push_back(passout); + } + ++curr_cell; + } + } + return chains; + } + + // Insert a logic cell to legalise a COUT->fabric connection CellInfo *make_carry_pass_out(PortInfo &cout_port) { assert(cout_port.net != nullptr); CellInfo *lc = create_ice_cell(ctx, ctx->id("ICESTORM_LC")); lc->params[ctx->id("LUT_INIT")] = "65280"; // 0xff00: O = I3 + lc->params[ctx->id("CARRY_ENABLE")] = "1"; lc->ports.at(ctx->id("O")).net = cout_port.net; NetInfo *co_i3_net = new NetInfo(); co_i3_net->name = ctx->id(lc->name.str(ctx) + "$I3"); @@ -125,11 +178,18 @@ class PlacementLegaliser o_r.cell = lc; cout_port.net->driver = o_r; lc->ports.at(ctx->id("I3")).net = co_i3_net; + // I1=1 feeds carry up the chain, so no need to actually break the chain + lc->ports.at(ctx->id("I1")).net = ctx->nets.at(ctx->id("$PACKER_VCC_NET")); + PortRef i1_r; + i1_r.port = ctx->id("I1"); + i1_r.cell = lc; + ctx->nets.at(ctx->id("$PACKER_VCC_NET"))->users.push_back(i1_r); ctx->cells[lc->name] = lc; createdCells.insert(lc->name); return lc; } + // Insert a logic cell to legalise a CIN->fabric connection CellInfo *make_carry_feed_in(CellInfo *cin_cell, PortInfo &cin_port) { assert(cin_port.net != nullptr); -- cgit v1.2.3