fix(cpu): Delay IRQ by one clock after CLI is called

gabe565 · Aug 26, 2024 · 48783d5 · 48783d5
1 parent 9433b19
commit 48783d5
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Showing 2 changed files with 7 additions and 1 deletion.
diff --git a/internal/cpu/cpu.go b/internal/cpu/cpu.go
@@ -52,6 +52,7 @@ type CPU struct {
 
 	NMIPending bool `msgpack:"alias:NmiPending"`
 	IRQPending bool `msgpack:"alias:IrqPending"`
+	irqDelay   uint8
 
 	Stall uint16
 
@@ -99,7 +100,11 @@ func (c *CPU) Step() uint {
 	if c.NMIPending {
 		c.nmi()
 	} else if c.IRQPending && !c.Status.InterruptDisable {
-		c.irq()
+		if c.irqDelay == 0 {
+			c.irq()
+		} else {
+			c.irqDelay--
+		}
 	}
 
 	code := c.ReadMem(c.ProgramCounter)

diff --git a/internal/cpu/instructions.go b/internal/cpu/instructions.go
@@ -326,6 +326,7 @@ func cld(c *CPU, _ AddressingMode) {
 // [CLI Instruction Reference]: https://www.nesdev.org/obelisk-6502-guide/reference.html#CLI
 func cli(c *CPU, _ AddressingMode) {
 	c.Status.InterruptDisable = false
+	c.irqDelay = 1
 }
 
 // clv - Clear Overflow Flag