esp-idf/examples/peripherals/rmt_tx/main/rmt_tx_main.c

/* RMT transmit example

   This example code is in the Public Domain (or CC0 licensed, at your option.)

   Unless required by applicable law or agreed to in writing, this
   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
   CONDITIONS OF ANY KIND, either express or implied.
*/
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_log.h"
#include "driver/rmt.h"

static const char *RMT_TX_TAG = "RMT Tx";

#define RMT_TX_CHANNEL RMT_CHANNEL_0
#define RMT_TX_GPIO 18
#define SAMPLE_CNT  (10)

/*
 * Prepare a raw table with a message in the Morse code
 *
 * The message is "ESP" : . ... .--.
 *
 * The table structure represents the RMT item structure:
 * {duration, level, duration, level}
 *
 */
rmt_item32_t items[] = {
    // E : dot
    {{{ 32767, 1, 32767, 0 }}}, // dot
    //
    {{{ 32767, 0, 32767, 0 }}}, // SPACE
    // S : dot, dot, dot
    {{{ 32767, 1, 32767, 0 }}}, // dot
    {{{ 32767, 1, 32767, 0 }}}, // dot
    {{{ 32767, 1, 32767, 0 }}}, // dot
    //
    {{{ 32767, 0, 32767, 0 }}}, // SPACE
    // P : dot, dash, dash, dot
    {{{ 32767, 1, 32767, 0 }}}, // dot
    {{{ 32767, 1, 32767, 1 }}},
    {{{ 32767, 1, 32767, 0 }}}, // dash
    {{{ 32767, 1, 32767, 1 }}},
    {{{ 32767, 1, 32767, 0 }}}, // dash
    {{{ 32767, 1, 32767, 0 }}}, // dot

    // RMT end marker
    {{{ 0, 1, 0, 0 }}}
};

//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 = {{{ 32767, 1, 15000, 0 }}}; //Logical 0
    const rmt_item32_t bit1 = {{{ 32767, 1, 32767, 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++) {
            if(*psrc & (0x1 << i)) {
                pdest->val =  bit1.val; 
            } else {
                pdest->val =  bit0.val;
            }
            num++;
            pdest++;
        }
        size++;
        psrc++;
    }
    *translated_size = size;
    *item_num = num;
}

/*
 * Initialize the RMT Tx channel
 */
static void rmt_tx_int()
{
    rmt_config_t config;
    config.rmt_mode = RMT_MODE_TX;
    config.channel = RMT_TX_CHANNEL;
    config.gpio_num = RMT_TX_GPIO;
    config.mem_block_num = 1;
    config.tx_config.loop_en = 0;
    // enable the carrier to be able to hear the Morse sound
    // if the RMT_TX_GPIO is connected to a speaker
    config.tx_config.carrier_en = 1;
    config.tx_config.idle_output_en = 1;
    config.tx_config.idle_level = 0;
    config.tx_config.carrier_duty_percent = 50;
    // set audible career frequency of 611 Hz
    // actually 611 Hz is the minimum, that can be set
    // with current implementation of the RMT API
    config.tx_config.carrier_freq_hz = 611;
    config.tx_config.carrier_level = 1;
    // set the maximum clock divider to be able to output
    // RMT pulses in range of about one hundred milliseconds
    config.clk_div = 255;

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

void app_main(void *ignore)
{
    ESP_LOGI(RMT_TX_TAG, "Configuring transmitter");
    rmt_tx_int();
    int number_of_items = sizeof(items) / sizeof(items[0]);
    const uint8_t sample[SAMPLE_CNT] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

    while (1) {
        ESP_ERROR_CHECK(rmt_write_items(RMT_TX_CHANNEL, items, number_of_items, true));
        ESP_LOGI(RMT_TX_TAG, "Transmission complete");
        vTaskDelay(1000 / portTICK_PERIOD_MS);
        ESP_ERROR_CHECK(rmt_write_sample(RMT_TX_CHANNEL, sample, SAMPLE_CNT, true));
        ESP_LOGI(RMT_TX_TAG, "Sample transmission complete");
        vTaskDelay(2000 / portTICK_PERIOD_MS);
    }
    vTaskDelete(NULL);
}