/*
  Smooth Frequency Sweep (DDS) on DAC (SAMD21 XIAO)
  -------------------------------------------------
  Generates a smooth sine wave on DAC A0, sweeping up and down
  between freq_start and freq_stop over sweep_period milliseconds.

  Uses:
    - Direct Digital Synthesis (DDS)
    - Timer TC5 for precise DAC timing

  Hardware:
    Seeeduino XIAO (SAMD21)
    DAC output on A0 (D0)
*/

#include <Arduino.h>
#include <math.h>

// ===== USER PARAMETERS =====
const float freq_start   = 100.0;     // Hz
const float freq_stop    = 1000.0;    // Hz
const unsigned long sweep_period = 5000; // ms (up + down)
const uint16_t amplitude = 2047;      // Max 4095 (12-bit DAC)

// ===== INTERNAL CONSTANTS =====
const uint16_t TABLE_SIZE = 256;      // Sine lookup table size
const float SAMPLE_RATE = 48000.0;    // DAC sample rate (Hz)

volatile uint16_t sineTable[TABLE_SIZE];
volatile uint32_t phaseAcc = 0;       // 32-bit phase accumulator
volatile uint32_t phaseInc = 0;       // Phase increment per sample

// DAC pin
const int dacPin = A0;

// Sweep control
unsigned long sweepStart = 0;
float currentFreq = freq_start;

// ===== TIMER ISR =====
void TC5_Handler(void) {
  // Clear interrupt flag
  TC5->COUNT16.INTFLAG.bit.MC0 = 1;

  // Increment phase accumulator
  phaseAcc += phaseInc;

  // Lookup sine sample
  uint16_t index = (phaseAcc >> 24) & 0xFF; // top 8 bits for 256-entry table
  analogWrite(dacPin, sineTable[index]);
}

// ===== SETUP FUNCTIONS =====
void setupSineTable() {
  for (uint16_t i = 0; i < TABLE_SIZE; i++) {
    float theta = (2.0f * PI * i) / TABLE_SIZE;
    sineTable[i] = amplitude + (uint16_t)(amplitude * sin(theta));
  }
}

void setupTimer() {
  // Enable GCLK for TC5
  GCLK->CLKCTRL.reg = GCLK_CLKCTRL_ID(TC5_GCLK_ID) |
                      GCLK_CLKCTRL_GEN_GCLK0 |
                      GCLK_CLKCTRL_CLKEN;
  while (GCLK->STATUS.bit.SYNCBUSY);

  // Disable timer
  TC5->COUNT16.CTRLA.reg &= ~TC_CTRLA_ENABLE;
  while (TC5->COUNT16.STATUS.bit.SYNCBUSY);

  // Configure timer for match frequency mode
  TC5->COUNT16.CTRLA.reg = TC_CTRLA_MODE_COUNT16 |
                           TC_CTRLA_WAVEGEN_MFRQ |
                           TC_CTRLA_PRESCALER_DIV1;

  // Set compare value for desired sample rate
  uint32_t compareValue = (uint32_t)(SystemCoreClock / SAMPLE_RATE);
  TC5->COUNT16.CC[0].reg = compareValue;
  while (TC5->COUNT16.STATUS.bit.SYNCBUSY);

  // Enable interrupt
  NVIC_EnableIRQ(TC5_IRQn);
  TC5->COUNT16.INTENSET.bit.MC0 = 1;

  // Enable timer
  TC5->COUNT16.CTRLA.reg |= TC_CTRLA_ENABLE;
  while (TC5->COUNT16.STATUS.bit.SYNCBUSY);
}

void setup() {
  analogWriteResolution(12);
  pinMode(dacPin, OUTPUT);
  setupSineTable();
  setupTimer();
  sweepStart = millis();
}

// ===== MAIN LOOP =====
void loop() {
  // Determine where we are in the sweep
  unsigned long elapsed = (millis() - sweepStart) % sweep_period;
  float half = sweep_period / 2.0;

  // Linear sweep up and down
  if (elapsed < half)
    currentFreq = freq_start + (freq_stop - freq_start) * (elapsed / half);
  else
    currentFreq = freq_stop - (freq_stop - freq_start) * ((elapsed - half) / half);

  // Update phase increment (DDS)
  // phaseInc = (currentFreq / SAMPLE_RATE) * 2^32
  phaseInc = (uint32_t)((currentFreq * 4294967296.0) / SAMPLE_RATE);
}