Bit-banging a WS2812/WS2812B LED on Nordic nRF51 platform (nRF51422 or nRF51822)

nrf_ws2812.h

#define NOP() __asm volatile ( "NOP" )

void ws2812_init(void)
{
  NRF_GPIO->PIN_CNF[PIN_WS_DIN] = (GPIO_PIN_CNF_DIR_Output << GPIO_PIN_CNF_DIR_Pos)
                                | (GPIO_PIN_CNF_INPUT_Disconnect << GPIO_PIN_CNF_INPUT_Pos)
                                | (GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos)
                                | (GPIO_PIN_CNF_DRIVE_S0S1 << GPIO_PIN_CNF_DRIVE_Pos)
                                | (GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos);
}

void ws2812_rgb(uint8_t r, uint8_t g, uint8_t b)
{
  const uint8_t END = 1;
  int32_t a = (g<<24)|(r<<16)|(b<<8)|END;
  while (1) {
    if (a==END<<24)
      break;
    NRF_GPIO->OUTSET = (1<<PIN_WS_DIN);
    if (a >= 0)
    {
      a <<= 1;
      NOP();
      NRF_GPIO->OUTCLR = (1<<PIN_WS_DIN);
      NOP();
      NOP();
      NOP();
      NOP();
    }
    else
    {
      a <<= 1;
      NOP();
      NOP();
      NOP();
      NOP();
      NOP();
      NOP();
      NRF_GPIO->OUTCLR = (1<<PIN_WS_DIN);
      NOP();
    }
  }
}

This code assumes the CPU runs at 16MHz.

curious if you're using a level shifter or if you've manage to get it working at 3.3v.