fix(cpu): event system issue

`updateClockEvent()` and `clearClockEvent()` would sometimes mess up the list of events.
This could cause unexpected behavior when you have multiple timers running.

Also added regression tests for these methods.

2 files changed, 63 insertions, 2 deletions

diff --git a/src/cpu/cpu.spec.ts b/src/cpu/cpu.spec.ts
index a68f754..00fbcb3 100644
--- a/src/cpu/cpu.spec.ts
+++ b/src/cpu/cpu.spec.ts
@@ -5,4 +5,65 @@ describe('cpu', () => {
     const cpu = new CPU(new Uint16Array(1024), 0x1000);
     expect(cpu.SP).toEqual(0x10ff);
   });
+
+  describe('events', () => {
+    it('should execute queued events after the given number of cycles has passed', () => {
+      const cpu = new CPU(new Uint16Array(1024), 0x1000);
+      const events = [];
+      for (const i of [1, 4, 10]) {
+        cpu.addClockEvent(() => events.push([i, cpu.cycles]), i);
+      }
+      for (let i = 0; i < 10; i++) {
+        cpu.cycles++;
+        cpu.tick();
+      }
+      expect(events).toEqual([
+        [1, 1],
+        [4, 4],
+        [10, 10],
+      ]);
+    });
+
+    describe('updateClockEvent', () => {
+      it('should update the number of cycles for the given clock event', () => {
+        const cpu = new CPU(new Uint16Array(1024), 0x1000);
+        const events = [];
+        const callbacks = [];
+        for (const i of [1, 4, 10]) {
+          callbacks[i] = cpu.addClockEvent(() => events.push([i, cpu.cycles]), i);
+        }
+        cpu.updateClockEvent(callbacks[4], 2);
+        cpu.updateClockEvent(callbacks[1], 12);
+        for (let i = 0; i < 14; i++) {
+          cpu.cycles++;
+          cpu.tick();
+        }
+        expect(events).toEqual([
+          [4, 2],
+          [10, 10],
+          [1, 12],
+        ]);
+      });
+
+      describe('clearClockEvent', () => {
+        it('should remove the given clock event', () => {
+          const cpu = new CPU(new Uint16Array(1024), 0x1000);
+          const events = [];
+          const callbacks = [];
+          for (const i of [1, 4, 10]) {
+            callbacks[i] = cpu.addClockEvent(() => events.push([i, cpu.cycles]), i);
+          }
+          cpu.clearClockEvent(callbacks[4]);
+          for (let i = 0; i < 10; i++) {
+            cpu.cycles++;
+            cpu.tick();
+          }
+          expect(events).toEqual([
+            [1, 1],
+            [10, 10],
+          ]);
+        });
+      });
+    });
+  });
 });
diff --git a/src/cpu/cpu.ts b/src/cpu/cpu.ts
index fb98786..e7a2544 100644
--- a/src/cpu/cpu.ts
+++ b/src/cpu/cpu.ts
@@ -186,7 +186,7 @@ export class CPU implements ICPU {
   }
 
   updateClockEvent(callback: AVRClockEventCallback, cycles: number) {
-    const entry = this.clockEvents.find((item) => (item.callback = callback));
+    const entry = this.clockEvents.find((item) => item.callback === callback);
     if (entry) {
       entry.cycles = this.cycles + Math.max(1, cycles);
       this.updateClockEvents();
@@ -196,7 +196,7 @@ export class CPU implements ICPU {
   }
 
   clearClockEvent(callback: AVRClockEventCallback) {
-    const index = this.clockEvents.findIndex((item) => (item.callback = callback));
+    const index = this.clockEvents.findIndex((item) => item.callback === callback);
     if (index >= 0) {
       this.clockEvents.splice(index, 1);
       this.updateClockEvents();