2 files changed, 56 insertions, 13 deletions

diff --git a/src/peripherals/timer.spec.ts b/src/peripherals/timer.spec.ts
index 7750f26..9f50239 100644
--- a/src/peripherals/timer.spec.ts
+++ b/src/peripherals/timer.spec.ts
@@ -203,19 +203,62 @@ describe('timer', () => {
   });
 
   describe('16 bit timers', () => {
+    it('should increment 16-bit TCNT by 1', () => {
+      const timer = new AVRTimer(cpu, timer1Config);
+      cpu.writeData(0x85, 0x22); // TCNT1 <- 0x2233
+      cpu.writeData(0x84, 0x33); // ...
+      expect(timer.TCNT).toEqual(0x2233);
+      cpu.writeData(0x80, 0x0); // WGM1 <- 0 (Normal)
+      cpu.writeData(0x81, 0x1); // TCCR1B.CS <- 1
+      cpu.cycles = 1;
+      timer.tick();
+      expect(cpu.dataView.getUint16(0x84, true)).toEqual(0x2234); // TCNT1 should increment
+    });
+
     it('should set OCF0A flag when timer equals OCRA (16 bit mode)', () => {
       const timer = new AVRTimer(cpu, timer1Config);
       cpu.writeData(0x84, 0xee); // TCNT1 <- 0x10ee
       cpu.writeData(0x85, 0x10); // ...
       cpu.writeData(0x88, 0xef); // OCR1A <- 0x10ef
       cpu.writeData(0x89, 0x10); // ...
-      cpu.writeData(0x80, 0x0); // WGM1 <- 0 (Normal)
-      cpu.writeData(0x81, 0x1); // TCCR1B.CS <- 1
+      cpu.writeData(0x80, 0x0); // TCCR1A <- 0 (Normal Mode)
+      cpu.writeData(0x81, 0x1); // TCCR1B <- CS10
       cpu.cycles = 1;
       timer.tick();
-      expect(cpu.data[0x36]).toEqual(2); // TIFR0 should have OCF0A bit on
+      expect(cpu.data[0x36]).toEqual(2); // TIFR1 should have OCF1A bit on
       expect(cpu.pc).toEqual(0);
       expect(cpu.cycles).toEqual(1);
     });
+
+    it('should generate an overflow interrupt if timer overflows and interrupts enabled', () => {
+      const timer = new AVRTimer(cpu, timer1Config);
+      cpu.writeData(0x85, 0x3); // TCNT1 <- 0x3ff
+      cpu.writeData(0x84, 0xff); // ...
+      cpu.writeData(0x80, 0x3); // TCCR1A <- WGM10 | WGM11 (Fast PWM, 10-bit)
+      cpu.writeData(0x81, 0x9); // TCCR1B <- WGM12 | CS10
+      console.log(timer.CS);
+      cpu.data[0x6f] = 0x1; // TIMSK1: TOIE1
+      cpu.data[95] = 0x80; // SREG: I-------
+      cpu.cycles = 1;
+      timer.tick();
+      expect(cpu.dataView.getUint16(0x84, true)).toEqual(0); // TCNT should be 0
+      expect(cpu.data[0x36]).toEqual(0); // TOV bit in TIFR should be clear
+      expect(cpu.pc).toEqual(0x1a);
+      expect(cpu.cycles).toEqual(3);
+    });
+
+    it('should reset the timer once it reaches ICR value in mode 12', () => {
+      const timer = new AVRTimer(cpu, timer1Config);
+      cpu.writeData(0x85, 0x50); // TCNT1 <- 0x500f
+      cpu.writeData(0x84, 0x0f); // ...
+      cpu.writeData(0x87, 0x50); // ICR1 <- 0x5010
+      cpu.writeData(0x86, 0x10); // ...
+      cpu.writeData(0x81, 0x19); // TCCR1B <- WGM13 | WGM12 | CS10
+      cpu.cycles = 2; // 2 cycles should increment timer twice, beyond ICR1
+      timer.tick();
+      expect(cpu.dataView.getUint16(0x84, true)).toEqual(0); // TCNT should be 0
+      expect(cpu.data[0x36]).toEqual(0); // TOV bit in TIFR should be clear
+      expect(cpu.cycles).toEqual(2);
+    });
   });
 });
diff --git a/src/peripherals/timer.ts b/src/peripherals/timer.ts
index ea66671..6e805ee 100644
--- a/src/peripherals/timer.ts
+++ b/src/peripherals/timer.ts
@@ -206,11 +206,15 @@ export class AVRTimer {
     this.registerHook(config.OCRB, (value: u16) => {
       this.ocrB = value;
     });
-    cpu.writeHooks[config.TCCRA] = () => {
+    cpu.writeHooks[config.TCCRA] = (value) => {
+      this.cpu.data[config.TCCRA] = value;
       this.updateWGMConfig();
+      return true;
     };
-    cpu.writeHooks[config.TCCRB] = () => {
+    cpu.writeHooks[config.TCCRB] = (value) => {
+      this.cpu.data[config.TCCRB] = value;
       this.updateWGMConfig();
+      return true;
     };
   }
 
@@ -237,7 +241,7 @@ export class AVRTimer {
   set TCNT(value: u16) {
     this.cpu.data[this.config.TCNT] = value & 0xff;
     if (this.config.bits === 16) {
-      this.cpu.data[this.config.TCNT + 1] = (value >> 16) & 0xff;
+      this.cpu.data[this.config.TCNT + 1] = (value >> 8) & 0xff;
     }
   }
 
@@ -255,7 +259,7 @@ export class AVRTimer {
 
   get ICR() {
     // Only available for 16-bit timers
-    return this.cpu.data[this.config.ICR];
+    return (this.cpu.data[this.config.ICR + 1] << 8) | this.cpu.data[this.config.ICR];
   }
 
   get CS() {
@@ -280,12 +284,8 @@ export class AVRTimer {
 
   private registerHook(address: number, hook: (value: u16) => void) {
     if (this.config.bits === 16) {
-      this.cpu.writeHooks[address] = (value: u8) => {
-        hook(this.cpu.data[address + 1] | value);
-      };
-      this.cpu.writeHooks[address + 1] = (value: u8) => {
-        hook((value << 8) | this.cpu.data[address]);
-      };
+      this.cpu.writeHooks[address] = (value: u8) => hook((this.cpu.data[address + 1] << 8) | value);
+      this.cpu.writeHooks[address + 1] = (value: u8) => hook((value << 8) | this.cpu.data[address]);
     } else {
       this.cpu.writeHooks[address] = hook;
     }