Merge pull request #356 from YosysHQ/ecp5-ff-density
ecp5: Improve flipflop packing density
This commit is contained in:
David Shah
GitHub
commit
b4e9f5c3a6
153
ecp5/pack.cc
153
ecp5/pack.cc
@ -57,12 +57,14 @@ class Ecp5Packer
|
||||
}
|
||||
|
||||
// Print logic usgage
|
||||
int available_slices = 0;
|
||||
void print_logic_usage()
|
||||
{
|
||||
int total_luts = 0, total_ffs = 0;
|
||||
int total_ramluts = 0, total_ramwluts = 0;
|
||||
for (auto bel : ctx->getBels()) {
|
||||
if (ctx->getBelType(bel) == id_TRELLIS_SLICE) {
|
||||
available_slices += 1;
|
||||
total_luts += 2;
|
||||
total_ffs += 2;
|
||||
Loc l = ctx->getBelLocation(bel);
|
||||
@ -119,6 +121,58 @@ class Ecp5Packer
|
||||
}
|
||||
}
|
||||
|
||||
// Check if a flipflop is available in a slice
|
||||
bool is_ff_available(CellInfo *slice, int ff)
|
||||
{
|
||||
if (get_net_or_empty(slice, (ff == 1) ? id_Q1 : id_Q0) != nullptr)
|
||||
return false;
|
||||
if (get_net_or_empty(slice, (ff == 1) ? id_M1 : id_M0) != nullptr)
|
||||
return false;
|
||||
return true;
|
||||
}
|
||||
|
||||
// Check if a flipflop can be added to a slice
|
||||
bool can_add_ff_to_slice(CellInfo *slice, CellInfo *ff)
|
||||
{
|
||||
std::string clkmux = str_or_default(ff->params, ctx->id("CLKMUX"), "CLK");
|
||||
std::string lsrmux = str_or_default(ff->params, ctx->id("LSRMUX"), "LSR");
|
||||
|
||||
bool has_dpram = str_or_default(slice->params, ctx->id("MODE"), "LOGIC") == "DPRAM";
|
||||
if (has_dpram) {
|
||||
std::string wckmux = str_or_default(slice->params, ctx->id("WCKMUX"), "WCK");
|
||||
std::string wremux = str_or_default(slice->params, ctx->id("WREMUX"), "WRE");
|
||||
if (wckmux != clkmux && !(wckmux == "WCK" && clkmux == "CLK"))
|
||||
return false;
|
||||
if (wremux != lsrmux && !(wremux == "WRE" && lsrmux == "LSR"))
|
||||
return false;
|
||||
}
|
||||
bool has_ff0 = get_net_or_empty(slice, id_Q0) != nullptr;
|
||||
bool has_ff1 = get_net_or_empty(slice, id_Q1) != nullptr;
|
||||
if (!has_ff0 && !has_ff1)
|
||||
return true;
|
||||
if (str_or_default(ff->params, ctx->id("GSR"), "DISABLED") !=
|
||||
str_or_default(slice->params, ctx->id("GSR"), "DISABLED"))
|
||||
return false;
|
||||
if (str_or_default(ff->params, ctx->id("SRMODE"), "LSR_OVER_CE") !=
|
||||
str_or_default(slice->params, ctx->id("SRMODE"), "LSR_OVER_CE"))
|
||||
return false;
|
||||
if (str_or_default(ff->params, ctx->id("CEMUX"), "1") != str_or_default(slice->params, ctx->id("CEMUX"), "1"))
|
||||
return false;
|
||||
if (str_or_default(ff->params, ctx->id("LSRMUX"), "LSR") !=
|
||||
str_or_default(slice->params, ctx->id("LSRMUX"), "LSR"))
|
||||
return false;
|
||||
if (str_or_default(ff->params, ctx->id("CLKMUX"), "CLK") !=
|
||||
str_or_default(slice->params, ctx->id("CLKMUX"), "CLK"))
|
||||
return false;
|
||||
if (net_or_nullptr(ff, ctx->id("CLK")) != net_or_nullptr(slice, ctx->id("CLK")))
|
||||
return false;
|
||||
if (net_or_nullptr(ff, ctx->id("CE")) != net_or_nullptr(slice, ctx->id("CE")))
|
||||
return false;
|
||||
if (net_or_nullptr(ff, ctx->id("LSR")) != net_or_nullptr(slice, ctx->id("LSR")))
|
||||
return false;
|
||||
return true;
|
||||
}
|
||||
|
||||
const NetInfo *net_or_nullptr(CellInfo *cell, IdString port)
|
||||
{
|
||||
auto fnd = cell->ports.find(port);
|
||||
@ -1069,17 +1123,116 @@ class Ecp5Packer
|
||||
flush_cells();
|
||||
}
|
||||
|
||||
// Find a cell that meets some criterea near an origin cell
|
||||
// Used for packing an FF into a nearby SLICE
|
||||
template <typename TFunc> CellInfo *find_nearby_cell(CellInfo *origin, TFunc Func)
|
||||
{
|
||||
std::unordered_set<CellInfo *> visited_cells;
|
||||
std::queue<CellInfo *> to_visit;
|
||||
visited_cells.insert(origin);
|
||||
to_visit.push(origin);
|
||||
int iter = 0;
|
||||
while (!to_visit.empty() && iter < 10000) {
|
||||
CellInfo *cursor = to_visit.front();
|
||||
to_visit.pop();
|
||||
if (Func(cursor))
|
||||
return cursor;
|
||||
for (const auto &port : cursor->ports) {
|
||||
NetInfo *pn = port.second.net;
|
||||
if (pn == nullptr)
|
||||
continue;
|
||||
// Skip high-fanout nets that are unlikely to be relevant
|
||||
if (pn->users.size() > 25)
|
||||
continue;
|
||||
// Add other ports on this net if not already visited
|
||||
auto visit_port = [&](const PortRef &port) {
|
||||
if (port.cell == nullptr)
|
||||
return;
|
||||
if (visited_cells.count(port.cell))
|
||||
return;
|
||||
// If not already visited; add the cell of this port to the queue
|
||||
to_visit.push(port.cell);
|
||||
visited_cells.insert(port.cell);
|
||||
};
|
||||
visit_port(pn->driver);
|
||||
for (const auto &usr : pn->users)
|
||||
visit_port(usr);
|
||||
}
|
||||
++iter;
|
||||
}
|
||||
return nullptr;
|
||||
}
|
||||
|
||||
// Pack flipflops that weren't paired with a LUT
|
||||
float dense_pack_mode_thresh = 0.95f;
|
||||
void pack_remaining_ffs()
|
||||
{
|
||||
// Enter dense flipflop packing mode once utilisation exceeds a threshold (default: 95%)
|
||||
int used_slices = 0;
|
||||
for (auto &cell : ctx->cells)
|
||||
if (cell.second->type == id_TRELLIS_SLICE)
|
||||
++used_slices;
|
||||
|
||||
log_info("Packing unpaired FFs into a SLICE...\n");
|
||||
for (auto cell : sorted(ctx->cells)) {
|
||||
CellInfo *ci = cell.second;
|
||||
if (is_ff(ctx, ci)) {
|
||||
bool pack_dense = used_slices > (dense_pack_mode_thresh * available_slices);
|
||||
if (pack_dense) {
|
||||
// If dense packing threshold exceeded; always try and pack the FF into an existing slice
|
||||
// Find a SLICE with space "near" the flipflop in the netlist
|
||||
std::vector<CellInfo *> ltile;
|
||||
CellInfo *target = find_nearby_cell(ci, [&](CellInfo *cursor) {
|
||||
if (cursor->type != id_TRELLIS_SLICE)
|
||||
return false;
|
||||
if (!cursor->constr_children.empty() || cursor->constr_parent != nullptr) {
|
||||
auto &constr_children = (cursor->constr_parent != nullptr)
|
||||
? cursor->constr_parent->constr_children
|
||||
: cursor->constr_children;
|
||||
// Skip big chains for performance
|
||||
if (constr_children.size() > 8)
|
||||
return false;
|
||||
// Have to check the whole of the tile for legality when dealing with chains, not just slice
|
||||
ltile.clear();
|
||||
if (cursor->constr_parent != nullptr)
|
||||
ltile.push_back(cursor->constr_parent);
|
||||
else
|
||||
ltile.push_back(cursor);
|
||||
for (auto c : constr_children)
|
||||
ltile.push_back(c);
|
||||
if (!can_add_ff_to_tile(ltile, cursor))
|
||||
return false;
|
||||
}
|
||||
if (!can_add_ff_to_slice(cursor, ci))
|
||||
return false;
|
||||
for (int i = 0; i < 2; i++)
|
||||
if (is_ff_available(cursor, i))
|
||||
return true;
|
||||
return false;
|
||||
});
|
||||
|
||||
// If found, add the FF to this slice instead of creating a new one
|
||||
if (target != nullptr) {
|
||||
for (int i = 0; i < 2; i++) {
|
||||
if (is_ff_available(target, i)) {
|
||||
ff_to_slice(ctx, ci, target, i, false);
|
||||
goto ff_packed;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
if (false) {
|
||||
ff_packed:
|
||||
packed_cells.insert(ci->name);
|
||||
continue;
|
||||
}
|
||||
}
|
||||
|
||||
std::unique_ptr<CellInfo> slice =
|
||||
create_ecp5_cell(ctx, ctx->id("TRELLIS_SLICE"), ci->name.str(ctx) + "_SLICE");
|
||||
ff_to_slice(ctx, ci, slice.get(), 0, false);
|
||||
new_cells.push_back(std::move(slice));
|
||||
++used_slices;
|
||||
packed_cells.insert(ci->name);
|
||||
}
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user