archapi: Add new API for global constant routing

Signed-off-by: gatecat <[email protected]>

nexus/arch.h

@@ -1170,6 +1170,13 @@ struct Arch : BaseArch<ArchRanges>
     virtual bool checkWireAvail(WireId wire) const override { return getBoundWireNet(wire) == nullptr; }
     NetInfo *getBoundWireNet(WireId wire) const override { return tileStatus.at(wire.tile).boundwires.at(wire.index); }
 
+    IdString getWireConstantValue(WireId wire) const override
+    {
+        if (chip_wire_data(db, chip_info, wire).name == ID_LOCAL_VCC)
+            return id_VCC_DRV;
+        else
+            return {};
+    }
     // -------------------------------------------------
 
     PipId getPipByName(IdStringList name) const override;

nexus/pack.cc

@@ -325,6 +325,8 @@ struct NexusPacker
         CellInfo *new_cell = ctx->createCell(ctx->idf("$CONST_%s_DRV_", type.c_str(ctx)), type);
         new_cell->addOutput(id_Z);
         new_cell->connectPort(id_Z, new_net);
+        if (type == id_VCC_DRV)
+            new_net->constant_value = id_VCC_DRV;
         return new_net;
     }