esp8266/espneopixel.c

// Original version from https://github.com/adafruit/Adafruit_NeoPixel
// Modifications by dpgeorge to support auto-CPU-frequency detection

// This is a mash-up of the Due show() code + insights from Michael Miller's
// ESP8266 work for the NeoPixelBus library: github.com/Makuna/NeoPixelBus
// Needs to be a separate .c file to enforce ICACHE_RAM_ATTR execution.

#include "c_types.h"
#include "eagle_soc.h"
#include "user_interface.h"
#include "espneopixel.h"

#define NEO_KHZ400 (1)

static uint32_t _getCycleCount(void) __attribute__((always_inline));
static inline uint32_t _getCycleCount(void) {
  uint32_t ccount;
  __asm__ __volatile__("rsr %0,ccount":"=a" (ccount));
  return ccount;
}

void /*ICACHE_RAM_ATTR*/ esp_neopixel_write(uint8_t pin, uint8_t *pixels, uint32_t numBytes, bool is800KHz) {

  uint8_t *p, *end, pix, mask;
  uint32_t t, time0, time1, period, c, startTime, pinMask;

  pinMask   = 1 << pin;
  p         =  pixels;
  end       =  p + numBytes;
  pix       = *p++;
  mask      = 0x80;
  startTime = 0;

  uint32_t fcpu = system_get_cpu_freq() * 1000000;

#ifdef NEO_KHZ400
  if(is800KHz) {
#endif
    time0  = fcpu / 2500000; // 0.4us
    time1  = fcpu / 1250000; // 0.8us
    period = fcpu /  800000; // 1.25us per bit
#ifdef NEO_KHZ400
  } else { // 400 KHz bitstream
    time0  = fcpu / 2000000; // 0.5uS
    time1  = fcpu /  833333; // 1.2us
    period = fcpu /  400000; // 2.5us per bit
  }
#endif

  for(t = time0;; t = time0) {
    if(pix & mask) t = time1;                             // Bit high duration
    while(((c = _getCycleCount()) - startTime) < period); // Wait for bit start
    GPIO_REG_WRITE(GPIO_OUT_W1TS_ADDRESS, pinMask);       // Set high
    startTime = c;                                        // Save start time
    while(((c = _getCycleCount()) - startTime) < t);      // Wait high duration
    GPIO_REG_WRITE(GPIO_OUT_W1TC_ADDRESS, pinMask);       // Set low
    if(!(mask >>= 1)) {                                   // Next bit/byte
      if(p >= end) break;
      pix  = *p++;
      mask = 0x80;
    }
  }
  while((_getCycleCount() - startTime) < period); // Wait for last bit
}