ESP32 Forum

Posted: **Thu Sep 09, 2021 5:39 am**

I'm trying to use the RMT peripheral to bit-bang an array to a GPIO pin, but I'm not getting any output. I've gotten the expected output from the WS2812 driver example and used that example as a staring place for my implementation. I think the part that I'm having trouble understanding is the definition of rmt_item_t. If anyone can see what I'm doing wrong, please help! The code is below.

Code: Select all

#include "sdkconfig.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_log.h"
#include "driver/rmt.h"
#include "led_strip.h"
#include <string.h>

#define RMT_TX_CHANNEL RMT_CHANNEL_0
#define RMT_TX_PIN 21

#define DATA_LEN 10

static void IRAM_ATTR rmt_sample_to_rmt_t(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 = {{{500, 0, 0, 0}}}; //Logical 0
    const rmt_item32_t bit1 = {{{500, 1, 0, 0}}}; //Logical 1

    size_t size = 0;
    size_t num = 0;
    uint8_t *psrc = (uint8_t *)src;
    rmt_item32_t *pdest = dest;

    // loop over bytes in src array
    while (size < src_size && num < wanted_num)
    {
        for (int i = 0; i < 8; i++)
        {
            // LSB first
            if (*psrc & (1 << (i)))
                pdest->val = bit1.val;
            else
                pdest->val = bit0.val;
            num++;
            pdest++;
        }
        size++;
        psrc++;
    }
}

void app_main(void)
{
    rmt_config_t rmt_video_config = {.rmt_mode = RMT_MODE_TX,
                                     .channel = RMT_TX_CHANNEL,
                                     .gpio_num = RMT_TX_PIN,
                                     .clk_div = 16,  // 80MHz / 16 = 5MHz
                                     .mem_block_num = 1,
                                     .flags = 0,
                                     .tx_config = {
                                         .carrier_freq_hz = 22220 * 2,
                                         .carrier_level = RMT_CARRIER_LEVEL_HIGH,
                                         .idle_level = RMT_IDLE_LEVEL_LOW,
                                         .carrier_duty_percent = 50,
                                         .carrier_en = false,
                                         .loop_en = false,
                                         .idle_output_en = true}};

    // Configure and install RMT driver
    ESP_ERROR_CHECK(rmt_config(&rmt_video_config));
    ESP_ERROR_CHECK(rmt_driver_install(rmt_video_config.channel, 0, 0));
    ESP_ERROR_CHECK(rmt_translator_init(rmt_video_config.channel, rmt_sample_to_rmt_t));

    // fill an array with alternating zeros and ones
    uint8_t data[DATA_LEN] = {0};
    for (int i = 0; i < DATA_LEN; i++)
        data[i] = i % 2;

    while (1)
    {
        rmt_write_sample(rmt_video_config.channel, (const uint8_t *)&data, DATA_LEN, true);
        rmt_wait_tx_done(rmt_video_config.channel, 1000);

        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

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No output with RMT peripheral

No output with RMT peripheral