/* NeoPixel Driver using AVR Hardware and Events - see http://www.technoblogy.com/show?5BQG

   David Johnson-Davies - www.technoblogy.com - 20th August 2025
   AVR128DA28 @ 24 MHz (internal oscillator; BOD disabled)
   
   CC BY 4.0
   Licensed under a Creative Commons Attribution 4.0 International license: 
   http://creativecommons.org/licenses/by/4.0/
*/

const int NumPixels = 20;

union { uint8_t col[NumPixels][3]; uint8_t out[NumPixels*3]; } Buffer;
volatile int BufPtr;
enum colour { GRN, RED, BLU };

void setup() {

  // Configure Timer/Counter Type A to generate two waveforms
  PORTMUX.TCAROUTEA = PORTMUX_TCA0_PORTA_gc;              // Clear routing
  TCA0.SINGLE.CTRLD = 0;                                  // Normal mode
  PORTA.DIRSET = PIN0_bm | PIN1_bm;                       // WO0 and WO1 outputs
  TCA0.SINGLE.CTRLA = TCA_SINGLE_CLKSEL_DIV1_gc;          // Clock divided by 1
  TCA0.SINGLE.CTRLB = TCA_SINGLE_WGMODE_SINGLESLOPE_gc    // Single-slope PWM ...
    | TCA_SINGLE_CMP0EN_bm | TCA_SINGLE_CMP1EN_bm;        // waveform on WO0 and WO1
  TCA0.SINGLE.PER = 30-1;                                 // Period is 1250ns
  TCA0.SINGLE.CMP0 = 8-1;                                 // WO0 (PA0) is 333.33ns
  TCA0.SINGLE.CMP1 = 17-1;                                // WO1 (PA1) is 708.33ns

  // Configure SPI0 in client mode
  PORTA.DIRSET = PIN5_bm;                                 // MISO output
  SPI0.CTRLB = SPI_BUFEN_bm | SPI_BUFWR_bm                // Buffer mode ...
    | SPI_MODE_0_gc;                                      // transfer mode 0
  SPI0.CTRLA = SPI_ENABLE_bm;                             // Enable in client mode

  // Use CCL to make a gate between TCA0 WO0, TCA0 WO1, and MISO
  CCL.LUT1CTRLB = CCL_INSEL0_TCA0_gc | CCL_INSEL1_TCA0_gc;// TCA0 WO0 and WO1
  CCL.LUT1CTRLC = CCL_INSEL2_EVENTA_gc;                   // LUT1 EVENTA
  CCL.TRUTH1 = 0b11001010;
  CCL.LUT1CTRLA = CCL_OUTEN_bm | CCL_ENABLE_bm;           // Enable, output on PC3

  CCL.CTRLA = CCL_ENABLE_bm;                              // Enable CCL last

  // Use Events to copy the MISO output to LUT1 IN2
  EVSYS.CHANNEL0 = EVSYS_CHANNEL0_PORTA_PIN5_gc;          // Link PA5 ...
  EVSYS.USERCCLLUT1A = EVSYS_USER_CHANNEL0_gc;            // ... to LUT1 EVENTA

  // Use Events to copy PD4 to PA7
  PORTMUX.EVSYSROUTEA = PORTMUX_EVOUTA_ALT1_gc;           // EVOUTA on PA7
  EVSYS.CHANNEL2 = EVSYS_CHANNEL2_PORTD_PIN4_gc;          // Link PD4 ...
  EVSYS.USEREVSYSEVOUTA = EVSYS_USER_CHANNEL2_gc;         // ... and PA7

  // Pins
  PORTD.OUTSET = PIN4_bm;
  PORTD.DIRSET = PIN4_bm;                                 // PD4 EN output high
  PORTF.DIRSET = PIN0_bm;                                 // PF0 Error output low
}

ISR(SPI0_INT_vect) {
  if (BufPtr < NumPixels*3) {                             // More data to write?
    SPI0.DATA = Buffer.out[BufPtr++];                     // Output byte, clears flag
  } else if (SPI0.INTFLAGS & SPI_TXCIF_bm) {              // Shift register empty?
    PORTD.OUTSET = PIN4_bm;                               // Take EN high to stop SPI
    TCA0.SINGLE.CMP0 = 0;                                 // WO0 constant low signal
    TCA0.SINGLE.CMP1 = 0;                                 // WO1 constant low signal
    SPI0.INTFLAGS = SPI_TXCIF_bm;                         // Clear flag
    SPI0.INTCTRL = 0;                                     // Disable interrupts
  } else {
    SPI0.INTFLAGS = SPI_DREIF_bm;                         // Clear flag
    SPI0.INTCTRL = SPI0.INTCTRL &~SPI_DREIE_bm;           // Disable DREIF interrupt
  }
}

void StartTransfer () {
  BufPtr = 0;
  SPI0.DATA = Buffer.out[BufPtr++];                       // Initial data
  SPI0.DATA = Buffer.out[BufPtr++];                       // Initial data
  SPI0.INTCTRL = SPI_DREIE_bm | SPI_TXCIE_bm;             // Enable interrupts
  TCA0.SINGLE.CTRLA &= ~TCA_SINGLE_ENABLE_bm;             // Stop Timer/Counter
  TCA0.SINGLE.CMP0 = 8-1;                                 // WO0 (PA0) is 333.33ns
  TCA0.SINGLE.CMP1 = 17-1;                                // WO1 (PA1) is 708.33ns
  TCA0.SINGLE.CNT = 0;                                    // Clear Timer/Counter
  PORTD.OUTCLR = PIN4_bm;                                 // EN low to start output
  TCA0.SINGLE.CTRLA |= TCA_SINGLE_ENABLE_bm;              // Start Timer/Counter
}

// Demo - Colour Waves **********************************************

int fix (int y) {
  y = y % 768;
  if (y >= 256) y = 511 - y;
  if (y < 0) y = 0;
  return y;
}

void Waves () {
  unsigned long t = millis();
  StartTransfer();                                        // Runs under interrupt
  for (int p=0; p<NumPixels; p++) {                       // Update LEDs
    int c = t/10 + (768 * p)/20;
    while (BufPtr <= p*3);                                // Wait until output
    Buffer.col[p][GRN] = fix(c);
    Buffer.col[p][RED] = fix(c+256);
    Buffer.col[p][BLU] = fix(c+512);
  }
  if (millis() - t >= 20) PORTF.OUTSET = PIN0_bm;         // Error light
  else while (millis() - t < 20);                         // Wait until 20ms tick
}

void loop() {
  Waves();
}