Proposed fix for the behaviour of STP (#4)

* First fix for the behaviour of STP * Combining STP and JAM for better performance
visrealm · Feb 2, 2024 · 61f7371 · 61f7371
1 parent 07173c8
commit 61f7371
Showing 1 changed file with 7 additions and 6 deletions.
diff --git a/src/vrEmu6502.c b/src/vrEmu6502.c
@@ -59,6 +59,7 @@ struct vrEmu6502_s
   uint16_t currentOpcodeAddr;
 
   bool wai;
+  bool stp;
 
   uint16_t pc;
 
@@ -72,7 +73,6 @@ struct vrEmu6502_s
   uint16_t zpBase;
   uint16_t spBase;
   uint16_t tmpAddr;
-  bool jam;
 
   const vrEmu6502Opcode* opcodes;
   const char* mnemonicNames[256];
@@ -293,9 +293,9 @@ VR_EMU_6502_DLLEXPORT void vrEmu6502Reset(VrEmu6502* vr6502)
     vr6502->pc = read16(vr6502, RESET_VEC);
     vr6502->step = 0;
     vr6502->wai = false;
+    vr6502->stp = false;
     vr6502->currentOpcode = 0;
     vr6502->tmpAddr = 0;
-    vr6502->jam = 0;
 
     /* 65c02 clears D and sets I on reset */
     if (is65c02(vr6502))
@@ -325,7 +325,7 @@ static void beginInterrupt(VrEmu6502* vr6502, uint16_t addr)
  */
 VR_EMU_6502_DLLEXPORT void __time_critical_func(vrEmu6502Tick)(VrEmu6502* vr6502)
 {
-  if (vr6502->jam) return;
+  if (vr6502->stp) return;
 
   if (vr6502->step == 0)
   {
@@ -1789,8 +1789,9 @@ static void bbs7(VrEmu6502* vr6502, vrEmu6502AddrModeFn modeAddr) { bbs(vr6502,
  */
 static void stp(VrEmu6502* vr6502, vrEmu6502AddrModeFn modeAddr)
 {
-  if (modeAddr)
-    --vr6502->pc;
+  (void)modeAddr;
+
+  vr6502->stp = true;
 }
 
 /*
@@ -2006,7 +2007,7 @@ static void jam(VrEmu6502* vr6502, vrEmu6502AddrModeFn modeAddr)
   (void)modeAddr;
 
   vr6502->readFn(imm(vr6502), false);
-  vr6502->jam = 1;
+  vr6502->stp = true;
 }
 
 /* ------------------------------------------------------------------