2 files changed, 395 insertions, 0 deletions
diff --git a/src/peripherals/adc.spec.ts b/src/peripherals/adc.spec.ts
new file mode 100644
index 0000000..4eb9aff
--- /dev/null
+++ b/src/peripherals/adc.spec.ts
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+import { CPU } from '../cpu/cpu';
+import { asmProgram, TestProgramRunner } from '../utils/test-utils';
+import { AVRADC, adcConfig, ADCMuxInputType } from './adc';
+
+const R16 = 16;
+const R17 = 17;
+
+const ADMUX = 0x7c;
+const REFS0 = 1 << 6;
+
+const ADCSRA = 0x7a;
+const ADEN = 1 << 7;
+const ADSC = 1 << 6;
+const ADPS0 = 1 << 0;
+const ADPS1 = 1 << 1;
+const ADPS2 = 1 << 2;
+
+const ADCH = 0x79;
+const ADCL = 0x78;
+
+describe('ADC', () => {
+  it('should successfuly perform an ADC conversion', () => {
+    const { program } = asmProgram(`
+    ; register addresses
+    _REPLACE ADMUX, ${ADMUX}
+    _REPLACE ADCSRA, ${ADCSRA}
+    _REPLACE ADCH, ${ADCH}
+    _REPLACE ADCL, ${ADCL}
+
+    ; Configure mux - channel 0, reference: AVCC with external capacitor at AREF pin
+    ldi r24, ${REFS0}
+    sts ADMUX, r24
+
+    ; Start conversion with 128 prescaler
+    ldi r24, ${ADEN | ADSC | ADPS0 | ADPS1 | ADPS2}
+    sts ADCSRA, r24
+
+    ; Wait until conversion is complete
+  waitComplete:
+    lds r24, ${ADCSRA}
+    andi r24, ${ADSC}
+    brne waitComplete
+
+    ; Read the result
+    lds r16, ${ADCL}
+    lds r17, ${ADCH}
+
+    break
+  `);
+    const cpu = new CPU(program);
+    const adc = new AVRADC(cpu, adcConfig);
+    const runner = new TestProgramRunner(cpu);
+
+    const adcReadSpy = jest.spyOn(adc, 'onADCRead');
+    adc.channelValues[0] = 2.56; // should result in 2.56/5*1024 = 524
+
+    // Setup
+    runner.runInstructions(4);
+    expect(adcReadSpy).toHaveBeenCalledWith({ channel: 0, type: ADCMuxInputType.SingleEnded });
+
+    // Run the "waitComplete" loop for a few cycles
+    runner.runInstructions(12);
+
+    cpu.cycles += 128 * 25; // skip to the end of the conversion
+    cpu.tick();
+
+    // Now read the result
+    runner.runInstructions(5);
+
+    const low = cpu.data[R16];
+    const high = cpu.data[R17];
+    expect((high << 8) | low).toEqual(524); // 2.56 volts - see above
+  });
+
+  it('should read 0 when the ADC peripheral is not enabled', () => {
+    // This behavior was verified on real hardware, using the following test program:
+    // https://wokwi.com/arduino/projects/309156042450666050
+    // Thanks Oscar Oomens for spotting this!
+
+    const { program } = asmProgram(`
+    ; register addresses
+    _REPLACE ADMUX, ${ADMUX}
+    _REPLACE ADCSRA, ${ADCSRA}
+    _REPLACE ADCH, ${ADCH}
+    _REPLACE ADCL, ${ADCL}
+
+    ; Load some initial value into r16/r17 to make sure we actually read 0 later
+    ldi r16, 0xff
+    ldi r17, 0xff
+
+    ; Configure mux - channel 0, reference: AVCC with external capacitor at AREF pin
+    ldi r24, ${REFS0}
+    sts ADMUX, r24
+
+    ; Start conversion with 128 prescaler, but without enabling the ADC
+    ldi r24, ${ADSC | ADPS0 | ADPS1 | ADPS2}
+    sts ADCSRA, r24
+
+    ; Wait until conversion is complete
+  waitComplete:
+    lds r24, ${ADCSRA}
+    andi r24, ${ADSC}
+    brne waitComplete
+
+    ; Read the result
+    lds r16, ${ADCL}
+    lds r17, ${ADCH}
+
+    break
+  `);
+    const cpu = new CPU(program);
+    const adc = new AVRADC(cpu, adcConfig);
+    const runner = new TestProgramRunner(cpu, () => {
+      /* do nothing on break */
+    });
+
+    const adcReadSpy = jest.spyOn(adc, 'onADCRead');
+    adc.channelValues[0] = 2.56; // should result in 2.56/5*1024 = 524
+
+    // Setup
+    runner.runInstructions(6);
+    expect(adcReadSpy).not.toHaveBeenCalled();
+
+    // Run the "waitComplete" loop for a few cycles
+    runner.runInstructions(12);
+
+    cpu.cycles += 128 * 25; // skip to the end of the conversion
+    cpu.tick();
+
+    // Now read the result
+    runner.runToBreak();
+
+    const low = cpu.data[R16];
+    const high = cpu.data[R17];
+    expect((high << 8) | low).toEqual(0); // We should read 0 since the ADC hasn't been enabled
+  });
+});
diff --git a/src/peripherals/adc.ts b/src/peripherals/adc.ts
new file mode 100644
index 0000000..1e0e2d1
--- /dev/null
+++ b/src/peripherals/adc.ts
@@ -0,0 +1,258 @@
+/**
+ * AVR-8 ADC
+ * Part of AVR8js
+ * Reference: http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf
+ *
+ * Copyright (C) 2019, 2020, 2021 Uri Shaked
+ */
+
+import { AVRInterruptConfig, CPU } from '../cpu/cpu';
+import { u8 } from '../types';
+
+export enum ADCReference {
+  AVCC,
+  AREF,
+  Internal1V1,
+  Internal2V56,
+  Reserved,
+}
+
+export enum ADCMuxInputType {
+  SingleEnded,
+  Differential,
+  Constant,
+  Temperature,
+}
+
+export type ADCMuxInput =
+  | { type: ADCMuxInputType.Temperature }
+  | { type: ADCMuxInputType.Constant; voltage: number }
+  | { type: ADCMuxInputType.SingleEnded; channel: number }
+  | {
+      type: ADCMuxInputType.Differential;
+      positiveChannel: number;
+      negativeChannel: number;
+      gain: number;
+    };
+
+export type ADCMuxConfiguration = { [key: number]: ADCMuxInput };
+
+export interface ADCConfig {
+  ADMUX: u8;
+  ADCSRA: u8;
+  ADCSRB: u8;
+  ADCL: u8;
+  ADCH: u8;
+  DIDR0: u8;
+  adcInterrupt: u8;
+  numChannels: u8;
+  muxInputMask: u8;
+  muxChannels: ADCMuxConfiguration;
+  adcReferences: ADCReference[];
+}
+
+export const atmega328Channels: ADCMuxConfiguration = {
+  0: { type: ADCMuxInputType.SingleEnded, channel: 0 },
+  1: { type: ADCMuxInputType.SingleEnded, channel: 1 },
+  2: { type: ADCMuxInputType.SingleEnded, channel: 2 },
+  3: { type: ADCMuxInputType.SingleEnded, channel: 3 },
+  4: { type: ADCMuxInputType.SingleEnded, channel: 4 },
+  5: { type: ADCMuxInputType.SingleEnded, channel: 5 },
+  6: { type: ADCMuxInputType.SingleEnded, channel: 6 },
+  7: { type: ADCMuxInputType.SingleEnded, channel: 7 },
+  8: { type: ADCMuxInputType.Temperature },
+  14: { type: ADCMuxInputType.Constant, voltage: 1.1 },
+  15: { type: ADCMuxInputType.Constant, voltage: 0 },
+};
+
+const fallbackMuxInput = {
+  type: ADCMuxInputType.Constant,
+  voltage: 0,
+};
+
+export const adcConfig: ADCConfig = {
+  ADMUX: 0x7c,
+  ADCSRA: 0x7a,
+  ADCSRB: 0x7b,
+  ADCL: 0x78,
+  ADCH: 0x79,
+  DIDR0: 0x7e,
+  adcInterrupt: 0x2a,
+  numChannels: 8,
+  muxInputMask: 0xf,
+  muxChannels: atmega328Channels,
+  adcReferences: [
+    ADCReference.AREF,
+    ADCReference.AVCC,
+    ADCReference.Reserved,
+    ADCReference.Internal1V1,
+  ],
+};
+
+// Register bits:
+const ADPS_MASK = 0x7;
+const ADIE = 0x8;
+const ADIF = 0x10;
+const ADSC = 0x40;
+const ADEN = 0x80;
+
+const MUX_MASK = 0x1f;
+const ADLAR = 0x20;
+const MUX5 = 0x8;
+const REFS2 = 0x8;
+const REFS_MASK = 0x3;
+const REFS_SHIFT = 6;
+
+export class AVRADC {
+  /**
+   * ADC Channel values, in voltage (0..5). The number of channels depends on the chip.
+   *
+   * Changing the values here will change the ADC reading, unless you override onADCRead() with a custom implementation.
+   */
+  readonly channelValues = new Array(this.config.numChannels);
+
+  /** AVCC Reference voltage */
+  avcc = 5;
+
+  /** AREF Reference voltage */
+  aref = 5;
+
+  /**
+   * Invoked whenever the code performs an ADC read.
+   *
+   * The default implementation reads the result from the `channelValues` array, and then calls
+   * `completeADCRead()` after `sampleCycles` CPU cycles.
+   *
+   * If you override the default implementation, make sure to call `completeADCRead()` after
+   * `sampleCycles` cycles (or else the ADC read will never complete).
+   */
+  onADCRead: (input: ADCMuxInput) => void = (input) => {
+    // Default implementation
+    let voltage = 0;
+    switch (input.type) {
+      case ADCMuxInputType.Constant:
+        voltage = input.voltage;
+        break;
+      case ADCMuxInputType.SingleEnded:
+        voltage = this.channelValues[input.channel] ?? 0;
+        break;
+      case ADCMuxInputType.Differential:
+        voltage =
+          input.gain *
+          ((this.channelValues[input.positiveChannel] || 0) -
+            (this.channelValues[input.negativeChannel] || 0));
+        break;
+      case ADCMuxInputType.Temperature:
+        voltage = 0.378125; // 25 celcius
+        break;
+    }
+    const rawValue = (voltage / this.referenceVoltage) * 1024;
+    const result = Math.min(Math.max(Math.floor(rawValue), 0), 1023);
+    this.cpu.addClockEvent(() => this.completeADCRead(result), this.sampleCycles);
+  };
+
+  private converting = false;
+  private conversionCycles = 25;
+
+  // Interrupts
+  private ADC: AVRInterruptConfig = {
+    address: this.config.adcInterrupt,
+    flagRegister: this.config.ADCSRA,
+    flagMask: ADIF,
+    enableRegister: this.config.ADCSRA,
+    enableMask: ADIE,
+  };
+
+  constructor(private cpu: CPU, private config: ADCConfig) {
+    cpu.writeHooks[config.ADCSRA] = (value, oldValue) => {
+      if (value & ADEN && !(oldValue && ADEN)) {
+        this.conversionCycles = 25;
+      }
+      cpu.data[config.ADCSRA] = value;
+      cpu.updateInterruptEnable(this.ADC, value);
+      if (!this.converting && value & ADSC) {
+        if (!(value & ADEN)) {
+          // Special case: reading while the ADC is not enabled should return 0
+          this.cpu.addClockEvent(() => this.completeADCRead(0), this.sampleCycles);
+          return true;
+        }
+        let channel = this.cpu.data[this.config.ADMUX] & MUX_MASK;
+        if (cpu.data[config.ADCSRB] & MUX5) {
+          channel |= 0x20;
+        }
+        channel &= config.muxInputMask;
+        const muxInput = config.muxChannels[channel] ?? fallbackMuxInput;
+        this.converting = true;
+        this.onADCRead(muxInput);
+        return true; // don't update
+      }
+    };
+  }
+
+  completeADCRead(value: number) {
+    const { ADCL, ADCH, ADMUX, ADCSRA } = this.config;
+    this.converting = false;
+    this.conversionCycles = 13;
+    if (this.cpu.data[ADMUX] & ADLAR) {
+      this.cpu.data[ADCL] = (value << 6) & 0xff;
+      this.cpu.data[ADCH] = value >> 2;
+    } else {
+      this.cpu.data[ADCL] = value & 0xff;
+      this.cpu.data[ADCH] = (value >> 8) & 0x3;
+    }
+    this.cpu.data[ADCSRA] &= ~ADSC;
+    this.cpu.setInterruptFlag(this.ADC);
+  }
+
+  get prescaler() {
+    const { ADCSRA } = this.config;
+    const adcsra = this.cpu.data[ADCSRA];
+    const adps = adcsra & ADPS_MASK;
+    switch (adps) {
+      case 0:
+      case 1:
+        return 2;
+      case 2:
+        return 4;
+      case 3:
+        return 8;
+      case 4:
+        return 16;
+      case 5:
+        return 32;
+      case 6:
+        return 64;
+      case 7:
+      default:
+        return 128;
+    }
+  }
+
+  get referenceVoltageType() {
+    const { ADMUX, adcReferences } = this.config;
+    let refs = (this.cpu.data[ADMUX] >> REFS_SHIFT) & REFS_MASK;
+    if (adcReferences.length > 4 && this.cpu.data[ADMUX] & REFS2) {
+      refs |= 0x4;
+    }
+    return adcReferences[refs] ?? ADCReference.Reserved;
+  }
+
+  get referenceVoltage() {
+    switch (this.referenceVoltageType) {
+      case ADCReference.AVCC:
+        return this.avcc;
+      case ADCReference.AREF:
+        return this.aref;
+      case ADCReference.Internal1V1:
+        return 1.1;
+      case ADCReference.Internal2V56:
+        return 2.56;
+      default:
+        return this.avcc;
+    }
+  }
+
+  get sampleCycles() {
+    return this.conversionCycles * this.prescaler;
+  }
+}