gatemate: Override router2 cost function to account for low-delay pips

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

himbaechel/arch.cc

@@ -300,7 +300,9 @@ bool Arch::route()
     if (router == "router1") {
         result = router1(getCtx(), Router1Cfg(getCtx()));
     } else if (router == "router2") {
-        router2(getCtx(), Router2Cfg(getCtx()));
+        Router2Cfg cfg(getCtx());
+        uarch->configureRouter2(cfg);
+        router2(getCtx(), cfg);
         result = true;
     } else {
         log_error("Himbächel architecture does not support router '%s'\n", router.c_str());

himbaechel/himbaechel_api.h

@@ -56,6 +56,7 @@ struct Context;
 
 struct PlacerHeapCfg;
 struct PlacerStaticCfg;
+struct Router2Cfg;
 
 namespace po = boost::program_options;
 
@@ -149,6 +150,8 @@ struct HimbaechelAPI
     virtual void configurePlacerHeap(PlacerHeapCfg &cfg) {};
     virtual void configurePlacerStatic(PlacerStaticCfg &cfg);
 
+    virtual void configureRouter2(Router2Cfg &cfg) {};
+
     virtual std::string getDefaultRouter() const { return "router1"; };
 
     virtual ~HimbaechelAPI() {};

himbaechel/uarch/gatemate/gatemate.cc

@@ -24,6 +24,7 @@
 #include "nextpnr_assertions.h"
 #include "placer_heap.h"
 #include "placer_static.h"
+#include "router2.h"
 
 #define GEN_INIT_CONSTIDS
 #define HIMBAECHEL_CONSTIDS "uarch/gatemate/constids.inc"
@@ -1079,6 +1080,15 @@ void GateMateImpl::configurePlacerStatic(PlacerStaticCfg &cfg)
     }
 }
 
+void GateMateImpl::configureRouter2(Router2Cfg &cfg) {
+    cfg.get_base_cost = [](Context *ctx, WireId wire, PipId pip, float crit_weight) {
+        float delay_cost = ctx->getDelayNS(ctx->getPipDelay(pip).maxDelay() + ctx->getWireDelay(wire).maxDelay() + ctx->getDelayEpsilon());
+        const float rr_cost = 0.5f; // fundamental cost of using a routing resource
+        return delay_cost + rr_cost * (1.0f - crit_weight);
+        // return delay_cost;
+    };
+}
+
 int GateMateImpl::get_dff_config(CellInfo *dff) const
 {
     int val = 0;

himbaechel/uarch/gatemate/gatemate.h

@@ -79,6 +79,7 @@ struct GateMateImpl : HimbaechelAPI
 
     void configurePlacerHeap(PlacerHeapCfg &cfg) override;
     void configurePlacerStatic(PlacerStaticCfg &cfg) override;
+    void configureRouter2(Router2Cfg &cfg) override;
 
     bool isPipInverting(PipId pip) const override;