ESP8266 WS2812 RGB LED Driver in C

The purpose of this repository is to provide a stand-alone routine in C to drive WS2812 (Neopixel) RGB LEDs from an ESP8266. The routine, ws2812_write(), is in user_main.c. (Also necessary is the small _getCycleCount() routine.) These routines can be copied into an existing project file or can be placed in a new project file.

My goal was to address the needs of developers, like myself, who want to get something working quickly and who are not currently using a larger environment on the ESP8266, such as Arduino or NodeMCU.

Example Usage

#define WS2812_LED_GPIO 2

static void ICACHE_FLASH_ATTR update_leds(void)
{
	uint8_t colors[21] = {0, 0, 0, 32, 0, 0,   0, 32, 0,   0, 0, 32,   32, 32, 0,  32, 0, 32,  0, 32, 32 };
	
	ws2812_write(WS2812_LED_GPIO, colors, 21);
}

Notes

• The color sequence is Green-Red-Blue (GRB) and not the traditional Red-Green-Blue (RGB)
• See AdaFruit's extensive NeoPixel Überguide

Credits

The ws2812_write() routine is copied from @kbeckmann's NodeMCU repository. For more information see the related post Bit-banging two pins simultaneously on ESP8266

The Makefile is copied from Tuan PM's MQTT repository. I flattened the directory structure and made some minor changes to the Makefile.

References

• @adafruit's Neopixel Library: Handles the ESP8266 and the ESP32
• @cnlohr's original ws2812 project
• @cnlohr's I2C approach to driving ws2812: Reduces the CPU load by offloading the waveform creation to the I2C core
• @kbeckmann's Single pin and two pin bit-banging: Provides a version of ws2812_write() that simultaneously updates the LEDs on two GPIO pins.
• Scargill's Tech Blog

GPIO Set-up

The ESP8266 pin must be configured as a GPIO pin.

For pin 2, for example, these lines are necessary:

    // Set pin mux for Pin 2 to "GPIO Alternate Function"
    PIN_FUNC_SELECT(PERIPHS_IO_MUX_GPIO2_U, FUNC_GPIO2); 
    
    // Enable pin 2
    GPIO_REG_WRITE(GPIO_ENABLE_W1TS_ADDRESS, (1<<2));

Routines (for copy-and-paste)

If you just want to get started and are not interested in the comments, then you can copy and paste these two routines. See user_main.c to read the comments for these routines.

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

static void ws2812_write(uint8_t pin, uint8_t *pixels, uint32_t length) 
{
	uint8_t *p, *end, pixel, mask;
	uint32_t t, t0h, t1h, ttot, c, start_time, pin_mask;

	pin_mask = 1 << pin;
	p =  pixels;
	end =  p + length;
	pixel = *p++;
	mask = 0x80;
	start_time = 0;
	t0h  = (1000 * system_get_cpu_freq()) / 3333;  // 0.30us (spec=0.35 +- 0.15)
	t1h  = (1000 * system_get_cpu_freq()) / 1666;  // 0.60us (spec=0.70 +- 0.15)
	ttot = (1000 * system_get_cpu_freq()) /  800;  // 1.25us (MUST be >= 1.25)

	ets_intr_lock();

	while (true)
	{
		t = (pixel & mask) ? t1h : t0h;

		while (((c = _getCycleCount()) - start_time) < ttot); // Wait for the previous bit to finish
		GPIO_REG_WRITE(GPIO_OUT_W1TS_ADDRESS, pin_mask);      // Set pin high
		
		start_time = c;                                       // Save the start time
		while (((c = _getCycleCount()) - start_time) < t);    // Wait for high time to finish
		GPIO_REG_WRITE(GPIO_OUT_W1TC_ADDRESS, pin_mask);      // Set pin low
		
		if (!(mask >>= 1))                 					  // Next bit/byte
		{                 
			if (p >= end)
				break;

			pixel= *p++;
			mask = 0x80;
		}
	}
	
	ets_intr_unlock();
}