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nexus: Bel search function for DCC placement

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Signed-off-by: David Shah <dave@ds0.me>
This commit is contained in:
David Shah 2020-10-14 11:55:04 +01:00
parent da1e3c8612
commit 2df4d212c3
1 changed files with 56 additions and 2 deletions
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58
nexus/pack.cc
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@ -24,6 +24,7 @@
#include "util.h"
#include <boost/algorithm/string.hpp>
#include <queue>
NEXTPNR_NAMESPACE_BEGIN
@ -529,7 +530,7 @@ struct NexusPacker
}
}
BelId get_io_bel(CellInfo *ci)
BelId get_bel_attr(const CellInfo *ci)
{
if (!ci->attrs.count(id_BEL))
return BelId();
@ -621,7 +622,7 @@ struct NexusPacker
rename_port(ctx, ci, id_O, id_B);
}
// Get the IO bel
BelId bel = get_io_bel(ci);
BelId bel = get_bel_attr(ci);
// Set the cell type to the bel type
IdString type = ctx->getBelType(bel);
NPNR_ASSERT(type != IdString());
@ -645,6 +646,59 @@ struct NexusPacker
trim_design();
}
// Using a BFS, search for bels of a given type either upstream or downstream of another cell
void find_connected_bels(const CellInfo *cell, IdString port, IdString dest_type, IdString dest_pin, int iter_limit,
std::vector<BelId> &candidates)
{
int iter = 0;
std::queue<WireId> visit;
std::unordered_set<WireId> seen_wires;
std::unordered_set<BelId> seen_bels;
BelId bel = get_bel_attr(cell);
NPNR_ASSERT(bel != BelId());
WireId start_wire = ctx->getBelPinWire(bel, port);
NPNR_ASSERT(start_wire != WireId());
PortType dir = ctx->getBelPinType(bel, port);
visit.push(start_wire);
while (!visit.empty() && (iter++ < iter_limit)) {
WireId cursor = visit.front();
// Check to see if we have reached a valid bel pin
for (auto bp : ctx->getWireBelPins(cursor)) {
if (ctx->getBelType(bp.bel) != dest_type)
continue;
if (dest_pin != IdString() && bp.pin != dest_pin)
continue;
if (seen_bels.count(bp.bel))
continue;
seen_bels.insert(bp.bel);
candidates.push_back(bp.bel);
}
// Search in the appropriate direction up/downstream of the cursor
if (dir == PORT_OUT) {
for (PipId p : ctx->getPipsDownhill(cursor))
if (ctx->checkPipAvail(p)) {
WireId dst = ctx->getPipDstWire(p);
if (seen_wires.count(dst))
continue;
seen_wires.insert(dst);
visit.push(dst);
}
} else {
for (PipId p : ctx->getPipsUphill(cursor))
if (ctx->checkPipAvail(p)) {
WireId src = ctx->getPipSrcWire(p);
if (seen_wires.count(src))
continue;
seen_wires.insert(src);
visit.push(src);
}
}
}
}
explicit NexusPacker(Context *ctx) : ctx(ctx) {}
void operator()()