05.05.2016 WS2811 / Arduino PoC - working!

///////////////////////////////////////
//
//  WS2811 Test Sketch
//
//  04.05.2016: First Version
//  05.05.2016: Manual timing via NOP doesn't work.
//              Switching to timer2 (PD3)
//              Finally works! https://youtu.be/hwUaI-tJ2UE
//
///////////////////////////////////////

/* Description of the WS2811 protocol:
 *
 * https://cdn-shop.adafruit.com/datasheets/WS2811.pdf
 *
 *  0 is 0.5µs high, 2µs low
 *  1 is 1.2µs high, 1.3µs low
 *  half of those values for the 800kHz modules
 *
 *  Timing between bits is less critical - 3µs are ok.
 *  >6-9µs leads to reset=latching the data to the LEDs
 *
 *  Thus trying bitbang on PD3
 *
 */

#define LEDNO 50
#define OFF 4
#define ON 9
#define BITLENGTH 20

uint8_t red = 0;
uint8_t green = 85;
uint8_t blue = 170;
uint8_t leds = 0;

void setup() {
  DDRD |= (1<<PD3);  // set PD3 as Output
  PORTD &= ~(1<<PD3);  // set PD3 low
  // disable Arduino lib timer 0
  TCCR0A = 0;
  TCCR0B = 0;

  TCCR2B = 0;  // reset TIMER2
  TCCR2A = 0;
  OCR2A = BITLENGTH;  // Total length of a bit for WS2811
  for (int i=0; i<LEDNO; i++) {
    send_bits(0, 0, 0);
  }
  delay_us(50);
}

inline void set_timer() {
  TIFR2 |= (1<<TOV2);  // Alternatively, TOV2 is cleared by writing a logic one to the flag
  while (!(TIFR2 & (1 << TOV2)));  // Wait for overflow to occur
  TCNT2 = 0;
}

void send_bits(byte red, byte green, byte blue) {
  cli();  // stop interrupts
  TCCR2A = (1 << COM2B1) | (1 << WGM21) | (1 << WGM20);  // FastPWM to OCR2A
  // COM2B1: Clear OC2B on Compare Match, set OC2B at BOTTOM
  // WGM21, WGM20: Fast PWM ...
  TCCR2B = (1 << WGM22) | (1 << CS20);  // No prescaling; starts PWM
  // WGM22: ... Fast PWM Top OCR2A; CS20 = No prescaler

// manual unrolling - ugly!
// red ...
  TCNT2 = 0;
  (red & (1<<7)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (red & (1<<6)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (red & (1<<5)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (red & (1<<4)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (red & (1<<3)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (red & (1<<2)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (red & (1<<1)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (red & (1<<0)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();

// green ...
  (green & (1<<7)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (green & (1<<6)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (green & (1<<5)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (green & (1<<4)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (green & (1<<3)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (green & (1<<2)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (green & (1<<1)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (green & (1<<0)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();

// blue ...
  (blue & (1<<7)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (blue & (1<<6)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (blue & (1<<5)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (blue & (1<<4)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (blue & (1<<3)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (blue & (1<<2)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (blue & (1<<1)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  set_timer();
  (blue & (1<<0)) ? OCR2B = ON : OCR2B = OFF;  // set timer for bit on or off
  TIFR2 |= (1<<TOV2);  // Alternatively, TOV2 is cleared by writing a logic one to the flag
  while (!(TIFR2 & (1 << TOV2)));  // Wait for overflow to occur

  sei();  // start interrupts
  while (TCNT2 < ON);
  TCCR2B = 0;  // Reset TIMER2 again
  TCCR2A = 0;  // and switching it off.
  PORTD &= ~(1<<PD3);  // set PD3 low
}

// --- some weirdo delay function --------------------------------------------
void delay_us (int16_t us) {
  for (uint16_t i=0; i<us; i++) {
      for (int j=0; j<16; j++) {
        asm volatile ("nop");
      }
  }
}

void loop() {
/*
  for (int i=0; i<LEDNO; i++) {
    red++;
    green++;
    blue++;
    send_bits(red, green, blue);
  }
  delay_us(50);
  delay_us(30000);
*/

// /*
  for (int k=0; k<3; k++) {
    switch (k) {
     case 0: red = 255; green = 0; blue = 0; break;
     case 1: red = 0; green = 255; blue = 0; break;
     case 2: red = 0; green = 0; blue = 255; break;
    }
    for (int i=0; i<LEDNO; i++) {
      for (int j=0; j<LEDNO; j++) {
        (i==j) ? send_bits(red, green, blue) : send_bits(0, 0, 0);
      }
      delay_us(50);
      delay_us(10000);
    }
  }
//  */
}