archapi: Add getArcDelayOverride

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

common/kernel/arch_api.h

@@ -119,6 +119,7 @@ template <typename R> struct ArchAPI : BaseCtx
     virtual bool getBudgetOverride(const NetInfo *net_info, const PortRef &sink, delay_t &budget) const = 0;
     virtual delay_t estimateDelay(WireId src, WireId dst) const = 0;
     virtual BoundingBox getRouteBoundingBox(WireId src, WireId dst) const = 0;
+    virtual bool getArcDelayOverride(const NetInfo *net_info, const PortRef &sink, DelayQuad &delay) const = 0;
     // Decal methods
     virtual typename R::DecalGfxRangeT getDecalGraphics(DecalId decal) const = 0;
     virtual DecalXY getBelDecal(BelId bel) const = 0;

common/kernel/base_arch.h

@@ -317,6 +317,10 @@ template <typename R> struct BaseArch : ArchAPI<R>
     {
         return false;
     }
+    virtual bool getArcDelayOverride(const NetInfo *net_info, const PortRef &sink, DelayQuad &delay) const override
+    {
+        return false;
+    }
 
     // Decal methods
     virtual typename R::DecalGfxRangeT getDecalGraphics(DecalId decal) const override

common/kernel/context.cc

@@ -128,6 +128,12 @@ delay_t Context::getNetinfoRouteDelay(const NetInfo *net_info, const PortRef &us
     if (src_wire == WireId())
         return 0;
 
+    DelayQuad quad_result;
+    if (getArcDelayOverride(net_info, user_info, quad_result)) {
+        // Arch overrides delay
+        return quad_result.maxDelay();
+    }
+
     delay_t max_delay = 0;
 
     for (auto dst_wire : getNetinfoSinkWires(net_info, user_info)) {
@@ -173,6 +179,11 @@ DelayQuad Context::getNetinfoRouteDelayQuad(const NetInfo *net_info, const PortR
 
     DelayQuad result(std::numeric_limits<delay_t>::max(), std::numeric_limits<delay_t>::lowest());
 
+    if (getArcDelayOverride(net_info, user_info, result)) {
+        // Arch overrides delay
+        return result;
+    }
+
     for (auto dst_wire : getNetinfoSinkWires(net_info, user_info)) {
         WireId cursor = dst_wire;
         DelayQuad delay{0};

docs/archapi.md

@@ -551,6 +551,14 @@ Overwrite or modify (in-place) the timing budget for a given arc. Returns a bool
 
 *BaseArch default: returns false*
 
+### bool getArcDelayOverride(const NetInfo \*net_info, const PortRef &sink, DelayQuad &delay) const
+
+This allows an arch to provide a more precise method for calculating the delay for a routed arc than
+summing wire and pip delays; for example a SPICE simulation. If available, `delay` should be set and
+`true` returned.
+
+*BaseArch default: returns false*
+
 Flow Methods
 ------------
 

fpga_interchange/arch.h

@@ -709,6 +709,11 @@ struct Arch : ArchAPI<ArchRanges>
     uint32_t getDelayChecksum(delay_t v) const final { return v; }
     bool getBudgetOverride(const NetInfo *net_info, const PortRef &sink, delay_t &budget) const final;
 
+    bool getArcDelayOverride(const NetInfo *net_info, const PortRef &sink, DelayQuad &delay) const final
+    {
+        return false;
+    }
+
     // -------------------------------------------------
 
     void place_iobufs(WireId pad_wire, NetInfo *net,