prevent NMI from occurring multiple times at almost the same timing

ichirin2501 · Feb 9, 2024 · 7affd81 · 7affd81
1 parent bb7afae
commit 7affd81
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Showing 2 changed files with 8 additions and 3 deletions.
diff --git a/nes/cpu.go b/nes/cpu.go
@@ -381,6 +381,11 @@ func (cpu *CPU) pollInterrupts() {
 	}
 }
 
+func (cpu *CPU) clearNMIInterruptState() {
+	cpu.nmiSignal = false
+	cpu.nmiTriggered = false
+}
+
 func (cpu *CPU) Read(addr uint16) byte {
 	cpu.bus.RunDMAIfOccurred(true)
 	cpu.pollInterruptSignals()

diff --git a/nes/instruction.go b/nes/instruction.go
@@ -470,10 +470,10 @@ func (cpu *CPU) brk() {
 	// As far as I checked with cpu_interrupts_v2/2-nmi_and_brk.nes,
 	// it seems to be expecting the NMI edge detector timing.
 	if cpu.nmiSignal || cpu.nmiTriggered {
-		cpu.nmiSignal = false
 		cpu.push(cpu.P.Byte() | 0x30)
 		cpu.P.SetInterruptDisable(true)
 		cpu.PC = cpu.read16(0xFFFA)
+		cpu.clearNMIInterruptState()
 	} else {
 		cpu.push(cpu.P.Byte() | 0x30)
 		cpu.P.SetInterruptDisable(true)
@@ -504,7 +504,6 @@ ref: https://www.nesdev.org/wiki/CPU_interrupts#IRQ_and_NMI_tick-by-tick_executi
 */
 func (cpu *CPU) nmi() {
 	cpu.interrupting = true
-	cpu.nmiSignal = false
 
 	cpu.Read(cpu.PC) // dummy read
 	cpu.Read(cpu.PC) // dummy read
@@ -513,6 +512,7 @@ func (cpu *CPU) nmi() {
 	cpu.P.SetInterruptDisable(true)
 	cpu.PC = cpu.read16(0xFFFA)
 
+	cpu.clearNMIInterruptState()
 	cpu.interrupting = false
 }
 
@@ -522,10 +522,10 @@ func (cpu *CPU) irq() {
 	cpu.Read(cpu.PC) // dummy read
 	cpu.push16(cpu.PC)
 	if cpu.nmiSignal || cpu.nmiTriggered {
-		cpu.nmiSignal = false
 		cpu.push(cpu.P.Byte() | 0x20)
 		cpu.P.SetInterruptDisable(true)
 		cpu.PC = cpu.read16(0xFFFA)
+		cpu.clearNMIInterruptState()
 	} else {
 		cpu.push(cpu.P.Byte() | 0x20)
 		cpu.P.SetInterruptDisable(true)