1 files changed, 92 insertions, 0 deletions
diff --git a/src/peripherals/clock.ts b/src/peripherals/clock.ts
new file mode 100644
index 0000000..1dbf4ba
--- /dev/null
+++ b/src/peripherals/clock.ts
@@ -0,0 +1,92 @@
+/**
+ * AVR8 Clock
+ * Part of AVR8js
+ * Reference: http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf
+ *
+ * Copyright (C) 2020, Uri Shaked
+ */
+
+import { CPU } from '../cpu/cpu';
+import { u32, u8 } from '../types';
+
+const CLKPCE = 128;
+
+export interface AVRClockConfig {
+  CLKPR: u8;
+}
+
+export const clockConfig: AVRClockConfig = {
+  CLKPR: 0x61,
+};
+
+const prescalers = [
+  1,
+  2,
+  4,
+  8,
+  16,
+  32,
+  64,
+  128,
+  256,
+
+  // The following values are "reserved" according to the datasheet, so we measured
+  // with a scope to figure them out (on ATmega328p)
+  2,
+  4,
+  8,
+  16,
+  32,
+  64,
+  128,
+];
+
+export class AVRClock {
+  private clockEnabledCycles = 0;
+  private prescalerValue = 1;
+  cyclesDelta = 0;
+
+  constructor(
+    private cpu: CPU,
+    private baseFreqHz: u32,
+    private config: AVRClockConfig = clockConfig
+  ) {
+    this.cpu.writeHooks[this.config.CLKPR] = (clkpr) => {
+      if ((!this.clockEnabledCycles || this.clockEnabledCycles < cpu.cycles) && clkpr === CLKPCE) {
+        this.clockEnabledCycles = this.cpu.cycles + 4;
+      } else if (this.clockEnabledCycles && this.clockEnabledCycles >= cpu.cycles) {
+        this.clockEnabledCycles = 0;
+        const index = clkpr & 0xf;
+        const oldPrescaler = this.prescalerValue;
+        this.prescalerValue = prescalers[index];
+        this.cpu.data[this.config.CLKPR] = index;
+        if (oldPrescaler !== this.prescalerValue) {
+          this.cyclesDelta =
+            (cpu.cycles + this.cyclesDelta) * (oldPrescaler / this.prescalerValue) - cpu.cycles;
+        }
+      }
+
+      return true;
+    };
+  }
+
+  get frequency() {
+    return this.baseFreqHz / this.prescalerValue;
+  }
+
+  get prescaler() {
+    return this.prescalerValue;
+  }
+
+  get timeNanos() {
+    return ((this.cpu.cycles + this.cyclesDelta) / this.frequency) * 1e9;
+  }
+
+  get timeMicros() {
+    return ((this.cpu.cycles + this.cyclesDelta) / this.frequency) * 1e6;
+  }
+
+  get timeMillis() {
+    return ((this.cpu.cycles + this.cyclesDelta) / this.frequency) * 1e3;
+  }
+}