blinky-esp/main/rmt_leds.cpp

static const char *TAG = "rmt_leds";
#include <esp_log.h>

#include <freertos/FreeRTOS.h>
#include <freertos/task.h>

#include "rmt_leds.hpp"


#define WS2811_PULSE_WIDTH_NS 1250

#define RMT_TX_CHANNEL RMT_CHANNEL_0


static int bit_ticks;


static void IRAM_ATTR ws2811_rmt_adapter(
            const void *src, rmt_item32_t *dest, size_t src_size,
            size_t wanted_num, size_t *translated_size, size_t *item_num
        ) {
    if (src == NULL || dest == NULL) {
        *translated_size = 0;
        *item_num = 0;
        return;
    }

    const uint32_t short_ticks = bit_ticks / 3;
    const uint32_t long_ticks = bit_ticks - short_ticks;
    const rmt_item32_t bit0 = {{{ short_ticks, 1, long_ticks, 0 }}}; // Logical 0
    const rmt_item32_t bit1 = {{{ long_ticks, 1, short_ticks, 0 }}}; // Logical 1
    size_t size = 0;
    size_t num = 0;
    uint8_t *psrc = (uint8_t *)src;
    rmt_item32_t *pdest = dest;
    while (size < src_size && num < wanted_num) {
        for (int i = 0; i < 8; i++) {
            // MSB first
            if (*psrc & (1 << (7 - i))) {
                pdest->val =  bit1.val;
            } else {
                pdest->val =  bit0.val;
            }
            num++;
            pdest++;
        }
        size++;
        psrc++;
    }

    *translated_size = size;
    *item_num = num;
}


RMT_LEDs::RMT_LEDs(gpio_num_t _gpio, int length) :
            LEDStrip(length), gpio(_gpio), channel(RMT_CHANNEL_MAX) {
    rmt_config_t config = RMT_DEFAULT_CONFIG_TX(gpio, RMT_TX_CHANNEL);
    // set counter clock to 40MHz
    config.clk_div = 2;

    ESP_ERROR_CHECK(rmt_config(&config));
    channel = config.channel;
    ESP_ERROR_CHECK(rmt_driver_install(channel, 0, 0));

    uint32_t counter_clk_hz = 0;
    int err = rmt_get_counter_clock(channel, &counter_clk_hz);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "Failed to read RMT counter: %d", err);
        return;
    }

    rmt_translator_init(channel, ws2811_rmt_adapter);

    // ns -> ticks
    bit_ticks = ((uint64_t)counter_clk_hz * WS2811_PULSE_WIDTH_NS) / 1e9;

    ESP_LOGI(TAG, "Each bit is %d RMT ticks", bit_ticks);

    configure(length);
}

RMT_LEDs::~RMT_LEDs() {
    ESP_ERROR_CHECK(rmt_driver_uninstall(channel));
}

void RMT_LEDs::configure(int n_leds) {
    // We don't own the RMT buffer
}

void RMT_LEDs::show() {
    esp_err_t err;

    err = rmt_wait_tx_done(channel, 0);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "RMT TX incomplete: %d", err);
        return;
    }

    err = rmt_write_sample(channel, (uint8_t*)pixels, length * 3, false);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "Failed to write sample to RMT: %d", err);
    }
}