feat(clock): Clock Prescale (CLKPR) support #68

close #68

1 files changed, 92 insertions, 0 deletions

diff --git a/src/peripherals/clock.spec.ts b/src/peripherals/clock.spec.ts
new file mode 100644
index 0000000..69fc832
--- /dev/null
+++ b/src/peripherals/clock.spec.ts
@@ -0,0 +1,92 @@
+import { CPU } from '../cpu/cpu';
+import { AVRClock, clockConfig } from './clock';
+
+// Clock Registers
+const CLKPC = 0x61;
+
+// Register bit names
+const CLKPCE = 128;
+
+describe('Clock', () => {
+  it('should set the prescaler when double-writing CLKPC', () => {
+    const cpu = new CPU(new Uint16Array(0x1000));
+    const clock = new AVRClock(cpu, 16e6, clockConfig);
+    cpu.writeData(CLKPC, CLKPCE);
+    cpu.writeData(CLKPC, 3); // Divide by 8 (2^3)
+    expect(clock.frequency).toEqual(2e6); // 2MHz
+    expect(cpu.readData(CLKPC)).toEqual(3);
+  });
+
+  it('should not update the prescaler if CLKPCE was not set CLKPC', () => {
+    const cpu = new CPU(new Uint16Array(0x1000));
+    const clock = new AVRClock(cpu, 16e6, clockConfig);
+    cpu.writeData(CLKPC, 3); // Divide by 8 (2^3)
+    expect(clock.frequency).toEqual(16e6); // still 16MHz
+    expect(cpu.readData(CLKPC)).toEqual(0);
+  });
+
+  it('should not update the prescaler if more than 4 cycles passed since setting CLKPCE', () => {
+    const cpu = new CPU(new Uint16Array(0x1000));
+    const clock = new AVRClock(cpu, 16e6, clockConfig);
+    cpu.writeData(CLKPC, CLKPCE);
+    cpu.cycles += 6;
+    cpu.writeData(CLKPC, 3); // Divide by 8 (2^3)
+    expect(clock.frequency).toEqual(16e6); // still 16MHz
+    expect(cpu.readData(CLKPC)).toEqual(0);
+  });
+
+  describe('prescaler property', () => {
+    it('should return the current prescaler value', () => {
+      const cpu = new CPU(new Uint16Array(0x1000));
+      const clock = new AVRClock(cpu, 16e6, clockConfig);
+      cpu.writeData(CLKPC, CLKPCE);
+      cpu.writeData(CLKPC, 5); // Divide by 32 (2^5)
+      cpu.cycles = 16e6;
+      expect(clock.prescaler).toEqual(32);
+    });
+  });
+
+  describe('time properties', () => {
+    it('should return current number of microseconds, derived from base freq + prescaler', () => {
+      const cpu = new CPU(new Uint16Array(0x1000));
+      const clock = new AVRClock(cpu, 16e6, clockConfig);
+      cpu.writeData(CLKPC, CLKPCE);
+      cpu.writeData(CLKPC, 2); // Divide by 4 (2^2)
+      cpu.cycles = 16e6;
+      expect(clock.timeMillis).toEqual(4000); // 4 seconds
+    });
+
+    it('should return current number of milliseconds, derived from base freq + prescaler', () => {
+      const cpu = new CPU(new Uint16Array(0x1000));
+      const clock = new AVRClock(cpu, 16e6, clockConfig);
+      cpu.writeData(CLKPC, CLKPCE);
+      cpu.writeData(CLKPC, 2); // Divide by 4 (2^2)
+      cpu.cycles = 16e6;
+      expect(clock.timeMicros).toEqual(4e6); // 4 seconds
+    });
+
+    it('should return current number of nanoseconds, derived from base freq + prescaler', () => {
+      const cpu = new CPU(new Uint16Array(0x1000));
+      const clock = new AVRClock(cpu, 16e6, clockConfig);
+      cpu.writeData(CLKPC, CLKPCE);
+      cpu.writeData(CLKPC, 2); // Divide by 4 (2^2)
+      cpu.cycles = 16e6;
+      expect(clock.timeNanos).toEqual(4e9); // 4 seconds
+    });
+
+    it('should correctly calculate time when changing the prescale value at runtime', () => {
+      const cpu = new CPU(new Uint16Array(0x1000));
+      const clock = new AVRClock(cpu, 16e6, clockConfig);
+      cpu.cycles = 16e6; // run 1 second at 16MHz
+      cpu.writeData(CLKPC, CLKPCE);
+      cpu.writeData(CLKPC, 2); // Divide by 4 (2^2)
+      cpu.cycles += 2 * 4e6; // run 2 more seconds at 4MhZ
+      expect(clock.timeMillis).toEqual(3000); // 3 seconds in total
+
+      cpu.writeData(CLKPC, CLKPCE);
+      cpu.writeData(CLKPC, 1); // Divide by 2 (2^1)
+      cpu.cycles += 0.5 * 8e6; // run 0.5 more seconds at 8MhZ
+      expect(clock.timeMillis).toEqual(3500); // 3.5 seconds in total
+    });
+  });
+});