1 files changed, 19 insertions, 0 deletions
diff --git a/src/cpu/interrupt.spec.ts b/src/cpu/interrupt.spec.ts
index cc54e3c..c64724d 100644
--- a/src/cpu/interrupt.spec.ts
+++ b/src/cpu/interrupt.spec.ts
@@ -16,4 +16,23 @@ describe('avrInterrupt', () => {
     expect(cpu.data[0x7f]).toEqual(0x5); // Return addr high
     expect(cpu.data[95]).toEqual(0b00000001); // SREG: -------C
   });
+
+  it('should push a 3-byte return address when running in 22-bit PC mode (issue #58)', () => {
+    const cpu = new CPU(new Uint16Array(0x80000));
+    expect(cpu.pc22Bits).toEqual(true);
+
+    cpu.pc = 0x10520;
+    cpu.data[94] = 0;
+    cpu.data[93] = 0x80; // SP <- 0x80
+    cpu.data[95] = 0b10000001; // SREG <- I------C
+
+    avrInterrupt(cpu, 5);
+    expect(cpu.cycles).toEqual(2);
+    expect(cpu.pc).toEqual(5);
+    expect(cpu.data[93]).toEqual(0x7d); // SP should decrement by 3
+    expect(cpu.data[0x80]).toEqual(0x20); // Return addr low
+    expect(cpu.data[0x7f]).toEqual(0x05); // Return addr high
+    expect(cpu.data[0x7e]).toEqual(0x1); // Return addr extended
+    expect(cpu.data[95]).toEqual(0b00000001); // SREG: -------C
+  });
 });