nexus: Add resource cost overrides

Signed-off-by: gatecat <gatecat@ds0.me>

nexus/arch.cc

@@ -705,6 +705,21 @@ void Arch::pre_routing()
         }
     }
 }
+namespace {
+float router2_base_cost(Context *ctx, WireId wire, PipId pip, float crit_weight)
+{
+    (void)crit_weight; // unused
+    if (pip != PipId()) {
+        auto &data = ctx->pip_data(pip);
+        if (data.flags & PIP_ZERO_RR_COST)
+            return 1e-12;
+        if (data.flags & PIP_DRMUX_C)
+            return 1e15;
+    }
+    return ctx->getDelayNS(ctx->getPipDelay(pip).maxDelay() + ctx->getWireDelay(wire).maxDelay() +
+                           ctx->getDelayEpsilon());
+}
+} // namespace
 
 bool Arch::route()
 {
@@ -719,7 +734,9 @@ bool Arch::route()
     if (router == "router1") {
         result = router1(getCtx(), Router1Cfg(getCtx()));
     } else if (router == "router2") {
-        router2(getCtx(), Router2Cfg(getCtx()));
+        Router2Cfg cfg(getCtx());
+        cfg.get_base_cost = router2_base_cost;
+        router2(getCtx(), cfg);
         result = true;
     } else {
         log_error("Nexus architecture does not support router '%s'\n", router.c_str());
@@ -1030,7 +1047,7 @@ const std::vector<std::string> Arch::availablePlacers = {"sa",
 
 };
 
-const std::string Arch::defaultRouter = "router1";
+const std::string Arch::defaultRouter = "router2";
 const std::vector<std::string> Arch::availableRouters = {"router1", "router2"};
 
 NEXTPNR_NAMESPACE_END

nexus/arch.h

@@ -87,6 +87,8 @@ enum PipFlags
 {
     PIP_FIXED_CONN = 0x8000,
     PIP_LUT_PERM = 0x4000,
+    PIP_ZERO_RR_COST = 0x2000,
+    PIP_DRMUX_C = 0x1000,
 };
 
 NPNR_PACKED_STRUCT(struct PipInfoPOD {