ESP32_RMT_Driver.h

#include "driver/rmt.h"

#define APB_CLK_MHZ 80 // default RMT CLK source (80MHz)
#define RMT_CLK_DIV  2 // RMT CLK divider
#define RMT_TICK (RMT_CLK_DIV * 1000 / APB_CLK_MHZ) // 25ns

// timing parameters for WS2812B LEDs. you may need to
// tweek these if you're using a different kind of LED
#define T1_TICKS      250 / RMT_TICK // 250ns
#define T2_TICKS      625 / RMT_TICK // 625ns
#define T3_TICKS      375 / RMT_TICK // 375ns
#define RESET_TICKS 50000 / RMT_TICK // 50us

/*
 * Convert uint8_t type of data to rmt format data.
 */
static void IRAM_ATTR u8_to_rmt(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 rmt_item32_t bit0 = { {{ T1_TICKS,            1, T2_TICKS + T3_TICKS, 0 }} }; //Logical 0
    const rmt_item32_t bit1 = { {{ T1_TICKS + T2_TICKS, 1, T3_TICKS           , 0 }} }; //Logical 1
    const rmt_item32_t reset = { {{ RESET_TICKS / 2      , 0, RESET_TICKS / 2      , 0 }} }; //Reset
    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) {
        if (size < src_size - 1) { // have more pixel data, so translate into RMT items
            (pdest++)->val = (*psrc & B10000000) ? bit1.val : bit0.val;
            (pdest++)->val = (*psrc & B01000000) ? bit1.val : bit0.val;
            (pdest++)->val = (*psrc & B00100000) ? bit1.val : bit0.val;
            (pdest++)->val = (*psrc & B00010000) ? bit1.val : bit0.val;
            (pdest++)->val = (*psrc & B00001000) ? bit1.val : bit0.val;
            (pdest++)->val = (*psrc & B00000100) ? bit1.val : bit0.val;
            (pdest++)->val = (*psrc & B00000010) ? bit1.val : bit0.val;
            (pdest++)->val = (*psrc & B00000001) ? bit1.val : bit0.val;
            num += 8;
        }
        else { // no more pixel data, last RMT item is the reset pulse
            (pdest++)->val = reset.val;
            num++;
        }
        size++;
        psrc++;
    }
    *translated_size = size;
    *item_num = num;
}

/*
 * Initialize the RMT Tx channel
 */
static void rmt_tx_int(rmt_channel_t channel, uint8_t gpio) {
    rmt_config_t config;
    config.rmt_mode = RMT_MODE_TX;
    config.channel = channel;
    config.gpio_num = gpio_num_t(gpio);
    config.clk_div = RMT_CLK_DIV;
    config.mem_block_num = 1; // 64 pulse "items" per block
    config.tx_config.loop_en = 0;
    config.tx_config.carrier_en = 0;
    config.tx_config.idle_output_en = 1;
    config.tx_config.idle_level = RMT_IDLE_LEVEL_LOW;

    rmt_config(&config);
    rmt_driver_install(config.channel, 0, 0);
    rmt_translator_init(config.channel, u8_to_rmt);
}