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ws2812 driver

Prerequisites

Expected STM32CubeMX configuration:

  1. Let's say you use timer 2, channel 3:

  1. Select prescaler and counter period. For 72 MHz clock, this should be 0 and 90 respectively.

  1. Enable DMA memory to peripheral:

  1. Enable global interrupt.

Usage example:

...
#include "rgb_color.h"
static Leds_Color_t leds;
...

void application_init() {
    ...
    ws2812bInit(3, &htim2, TIM_CHANNEL_3);
    ...
}

void application_set_red_blue_purple_colors() {
    // Set predefined Red color for the first LED
    rgbLedSetValue(&leds.colors[0], RGB_LED_RED_COLOR);

    // Set predefined Blue color for the second LED
    rgbLedSetValue(&leds.colors[1], RGB_LED_BLUE_COLOR);

    // Set custom color for the third LED
    leds.colors[2].shades.blue = 255;
    leds.colors[2].shades.green = 0;
    leds.colors[2].shades.red = 255;

    // Serialize colors to the DMA buffer and start it
    ws2812bSetColors(&leds);
    ws2812bStartOnce();
}

Implementation details

Reference: WS2812B datasheet

Required config for timer:

  • timer freq = 72 000 000
  • timer prescaller = 0
  • pwm period or 1 bit = 90 timer ticks = 1.25 us:
  • transfer bit=1 => T1H = 0.8 us => 57.6 ticks
  • transfer bit=0 => T0H = 0.4 us => 28.8 ticks

Performance:

Number of LEDs Bits required Duration
1 24 30 us
3 72 90 us
10 230 0.3 ms
15 345 0.45 ms
32 768 0.96 ms
216 5184 6.480 ms

RAM requirements:

  • LED's color buffer requires 3 bytes for each LED.
  • DMA serialization buffer requires 24 bytes for each LED.