Fix Timer IRQ Timing ( #141 )

pce-devel · Apr 9, 2024 · a813eb0 · a813eb0
1 parent 82fb278
commit a813eb0
Showing 1 changed file with 9 additions and 1 deletion.
diff --git a/mednafen/src/pce/huc6280.cpp b/mednafen/src/pce/huc6280.cpp
@@ -42,7 +42,10 @@ namespace MDFN_IEN_PCE
 INLINE void HuC6280::LastCycle(void)
 {
  /*assert(((P & I_FLAG) ? 0 : (uint32)~0) == PIMaskCache);*/
- IRQSample = (IRQlow & IRQMask) & PIMaskCache;
+
+ // TIMER interrupt to be tested after opcodes, not one cycle early
+ //
+ IRQSample = (((IRQlow & IRQMask) & PIMaskCache) & ~IQTIMER);
  IFlagSample = P & I_FLAG;
  ADDCYC(1);
 }
@@ -604,6 +607,11 @@ NO_INLINE void HuC6280::RunSub(void)
 	  }
          }
 
+         // TIMER interrupt to be tested after opcodes, not one cycle early
+         //
+         if (!IFlagSample)
+           IRQSample |= (IRQlow & IRQMask & IQTIMER);
+
 	 if(IRQSample | IRQlow)
 	 {
           if(MDFN_UNLIKELY(IRQSample & IQRESET))