cpu: add JAM instructions

1 files changed, 12 insertions, 0 deletions

diff --git a/cpu/cpu.go b/cpu/cpu.go
index 79199a2..fb673b7 100644
--- a/cpu/cpu.go
+++ b/cpu/cpu.go
@@ -16,6 +16,7 @@ type CPU struct {
 
 	Bus    Bus
 	Cycles uint64
+	Jammed bool
 
 	extraCycles int
 }
@@ -65,9 +66,13 @@ func (c *CPU) Reset() {
 	c.Status = FlagU | FlagI
 	c.PC = c.read16(vectorReset)
 	c.Cycles = 7
+	c.Jammed = false
 }
 
 func (c *CPU) IRQ() {
+	if c.Jammed {
+		return
+	}
 	if c.flag(FlagI) {
 		return
 	}
@@ -76,6 +81,9 @@ func (c *CPU) IRQ() {
 }
 
 func (c *CPU) NMI() {
+	if c.Jammed {
+		return
+	}
 	c.interrupt(vectorNMI, false)
 	c.Cycles += 7
 }
@@ -94,6 +102,10 @@ func (c *CPU) interrupt(vector uint16, brk bool) {
 }
 
 func (c *CPU) Step() int {
+	if c.Jammed {
+		c.Cycles++
+		return 1
+	}
 	before := c.Cycles
 
 	opcode := c.read(c.PC)