ecp5: Improve flipflop packing density
Signed-off-by: David Shah <dave@ds0.me>
This commit is contained in:
David Shah
parent
08cf545d9b
commit
aee2e01983
153
ecp5/pack.cc
153
ecp5/pack.cc
@ -57,12 +57,14 @@ class Ecp5Packer
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}
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// Print logic usgage
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int available_slices = 0;
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void print_logic_usage()
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{
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int total_luts = 0, total_ffs = 0;
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int total_ramluts = 0, total_ramwluts = 0;
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for (auto bel : ctx->getBels()) {
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if (ctx->getBelType(bel) == id_TRELLIS_SLICE) {
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available_slices += 1;
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total_luts += 2;
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total_ffs += 2;
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Loc l = ctx->getBelLocation(bel);
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@ -119,6 +121,58 @@ class Ecp5Packer
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}
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}
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// Check if a flipflop is available in a slice
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bool is_ff_available(CellInfo *slice, int ff)
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{
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if (get_net_or_empty(slice, (ff == 1) ? id_Q1 : id_Q0) != nullptr)
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return false;
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if (get_net_or_empty(slice, (ff == 1) ? id_M1 : id_M0) != nullptr)
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return false;
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return true;
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}
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// Check if a flipflop can be added to a slice
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bool can_add_ff_to_slice(CellInfo *slice, CellInfo *ff)
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{
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std::string clkmux = str_or_default(ff->params, ctx->id("CLKMUX"), "CLK");
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std::string lsrmux = str_or_default(ff->params, ctx->id("LSRMUX"), "LSR");
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bool has_dpram = str_or_default(slice->params, ctx->id("MODE"), "LOGIC") == "DPRAM";
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if (has_dpram) {
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std::string wckmux = str_or_default(slice->params, ctx->id("WCKMUX"), "WCK");
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std::string wremux = str_or_default(slice->params, ctx->id("WREMUX"), "WRE");
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if (wckmux != clkmux && !(wckmux == "WCK" && clkmux == "CLK"))
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return false;
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if (wremux != lsrmux && !(wremux == "WRE" && lsrmux == "LSR"))
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return false;
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}
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bool has_ff0 = get_net_or_empty(slice, id_Q0) != nullptr;
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bool has_ff1 = get_net_or_empty(slice, id_Q1) != nullptr;
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if (!has_ff0 && !has_ff1)
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return true;
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if (str_or_default(ff->params, ctx->id("GSR"), "DISABLED") !=
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str_or_default(slice->params, ctx->id("GSR"), "DISABLED"))
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return false;
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if (str_or_default(ff->params, ctx->id("SRMODE"), "LSR_OVER_CE") !=
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str_or_default(slice->params, ctx->id("SRMODE"), "LSR_OVER_CE"))
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return false;
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if (str_or_default(ff->params, ctx->id("CEMUX"), "1") != str_or_default(slice->params, ctx->id("CEMUX"), "1"))
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return false;
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if (str_or_default(ff->params, ctx->id("LSRMUX"), "LSR") !=
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str_or_default(slice->params, ctx->id("LSRMUX"), "LSR"))
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return false;
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if (str_or_default(ff->params, ctx->id("CLKMUX"), "CLK") !=
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str_or_default(slice->params, ctx->id("CLKMUX"), "CLK"))
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return false;
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if (net_or_nullptr(ff, ctx->id("CLK")) != net_or_nullptr(slice, ctx->id("CLK")))
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return false;
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if (net_or_nullptr(ff, ctx->id("CE")) != net_or_nullptr(slice, ctx->id("CE")))
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return false;
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if (net_or_nullptr(ff, ctx->id("LSR")) != net_or_nullptr(slice, ctx->id("LSR")))
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return false;
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return true;
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}
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const NetInfo *net_or_nullptr(CellInfo *cell, IdString port)
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{
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auto fnd = cell->ports.find(port);
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@ -1069,17 +1123,116 @@ class Ecp5Packer
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flush_cells();
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}
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// Find a cell that meets some criterea near an origin cell
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// Used for packing an FF into a nearby SLICE
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template <typename TFunc> CellInfo *find_nearby_cell(CellInfo *origin, TFunc Func)
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{
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std::unordered_set<CellInfo *> visited_cells;
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std::queue<CellInfo *> to_visit;
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visited_cells.insert(origin);
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to_visit.push(origin);
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int iter = 0;
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while (!to_visit.empty() && iter < 10000) {
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CellInfo *cursor = to_visit.front();
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to_visit.pop();
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if (Func(cursor))
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return cursor;
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for (const auto &port : cursor->ports) {
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NetInfo *pn = port.second.net;
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if (pn == nullptr)
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continue;
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// Skip high-fanout nets that are unlikely to be relevant
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if (pn->users.size() > 25)
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continue;
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// Add other ports on this net if not already visited
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auto visit_port = [&](const PortRef &port) {
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if (port.cell == nullptr)
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return;
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if (visited_cells.count(port.cell))
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return;
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// If not already visited; add the cell of this port to the queue
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to_visit.push(port.cell);
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visited_cells.insert(port.cell);
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};
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visit_port(pn->driver);
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for (const auto &usr : pn->users)
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visit_port(usr);
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}
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++iter;
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}
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return nullptr;
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}
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// Pack flipflops that weren't paired with a LUT
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float dense_pack_mode_thresh = 0.95f;
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void pack_remaining_ffs()
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{
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// Enter dense flipflop packing mode once utilisation exceeds a threshold (default: 95%)
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int used_slices = 0;
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for (auto &cell : ctx->cells)
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if (cell.second->type == id_TRELLIS_SLICE)
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++used_slices;
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log_info("Packing unpaired FFs into a SLICE...\n");
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for (auto cell : sorted(ctx->cells)) {
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CellInfo *ci = cell.second;
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if (is_ff(ctx, ci)) {
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bool pack_dense = used_slices > (dense_pack_mode_thresh * available_slices);
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if (pack_dense) {
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// If dense packing threshold exceeded; always try and pack the FF into an existing slice
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// Find a SLICE with space "near" the flipflop in the netlist
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std::vector<CellInfo *> ltile;
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CellInfo *target = find_nearby_cell(ci, [&](CellInfo *cursor) {
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if (cursor->type != id_TRELLIS_SLICE)
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return false;
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if (!cursor->constr_children.empty() || cursor->constr_parent != nullptr) {
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auto &constr_children = (cursor->constr_parent != nullptr)
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? cursor->constr_parent->constr_children
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: cursor->constr_children;
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// Skip big chains for performance
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if (constr_children.size() > 8)
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return false;
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// Have to check the whole of the tile for legality when dealing with chains, not just slice
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ltile.clear();
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if (cursor->constr_parent != nullptr)
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ltile.push_back(cursor->constr_parent);
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else
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ltile.push_back(cursor);
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for (auto c : constr_children)
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ltile.push_back(c);
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if (!can_add_ff_to_tile(ltile, cursor))
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return false;
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}
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if (!can_add_ff_to_slice(cursor, ci))
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return false;
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for (int i = 0; i < 2; i++)
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if (is_ff_available(cursor, i))
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return true;
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return false;
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});
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// If found, add the FF to this slice instead of creating a new one
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if (target != nullptr) {
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for (int i = 0; i < 2; i++) {
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if (is_ff_available(target, i)) {
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ff_to_slice(ctx, ci, target, i, false);
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goto ff_packed;
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}
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}
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}
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if (false) {
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ff_packed:
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packed_cells.insert(ci->name);
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continue;
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}
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}
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std::unique_ptr<CellInfo> slice =
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create_ecp5_cell(ctx, ctx->id("TRELLIS_SLICE"), ci->name.str(ctx) + "_SLICE");
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ff_to_slice(ctx, ci, slice.get(), 0, false);
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new_cells.push_back(std::move(slice));
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++used_slices;
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packed_cells.insert(ci->name);
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}
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}
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