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samples: drivers: add espressif rmt application
This sample application demonstrates usage of the Espressif RMT driver. Signed-off-by: Joel Guittet <joelguittet@gmail.com>
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‎samples/drivers/misc/espressif_rmt/CMakeLists.txt‎

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# Copyright (c) 2025 Joel Guittet (joelguittet@gmail.com)
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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(espressif_rmt)
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target_sources(app PRIVATE src/main.c src/led_strip_encoder.c)

‎samples/drivers/misc/espressif_rmt/Kconfig‎

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# Private config options for espressif_rmt sample
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# Copyright (c) 2025 Joel Guittet (joelguittet@gmail.com)
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# SPDX-License-Identifier: Apache-2.0
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mainmenu "Espressif RMT sample application"
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source "Kconfig.zephyr"

‎samples/drivers/misc/espressif_rmt/README.rst‎

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.. zephyr:code-sample:: rmt
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:name: Espressif Remote Control Transceiver (RMT)
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:relevant-api: rmt_interface
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Generate a WS2812 signal using the RMT driver API.
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Overview
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********
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This sample demonstrates how to use the :ref:`Espressif RMT driver API <rmt_api>`.
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You should connect a WS2812 strip to the RMT output of the board.
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Building and Running
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********************
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The RMT output is defined in the board's devicetree and pinmux file.
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Building and Running for esp32-devkitc
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======================================
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The sample can be built and executed for the
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:zephyr:board:`esp32_devkitc` as follows:
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.. zephyr-app-commands::
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:zephyr-app: samples/drivers/misc/espressif_rmt
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:board: esp32_devkitc/esp32/procpu
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:goals: build flash
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:compact:
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Sample output
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=============
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.. code-block:: console
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*** Booting Zephyr OS build v4.3.0-2805-g63ff14e3d8d0 ***
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Create RMT TX channel
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I (141) gpio: GPIO[12]| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
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Install led strip encoder
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Enable RMT TX channel
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Start LED rainbow chase
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After you seeing this log, you should see a rainbow chasing demonstration pattern.

‎samples/drivers/misc/espressif_rmt/prj.conf‎

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CONFIG_ESPRESSIF_RMT=y

‎samples/drivers/misc/espressif_rmt/sample.yaml‎

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sample:
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name: espressif_rmt
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tests:
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sample.drivers.misc.espressif_rmt:
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tags:
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- drivers
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filter: dt_compat_enabled("espressif,esp32-rmt")

‎samples/drivers/misc/espressif_rmt/socs/esp32_procpu.overlay‎

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/*
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* Copyright 2025 Joel Guittet (joelguittet@gmail.com)
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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/ {
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zephyr,user {
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rmt-output-gpios = <&gpio0 12 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
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};
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};
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&rmt {
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status = "okay";
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};

‎samples/drivers/misc/espressif_rmt/src/led_strip_encoder.c‎

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/*
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* SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include "esp_check.h"
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#include "led_strip_encoder.h"
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static const char *TAG = "led_encoder";
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typedef struct {
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rmt_encoder_t base;
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rmt_encoder_t *bytes_encoder;
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rmt_encoder_t *copy_encoder;
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int state;
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rmt_symbol_word_t reset_code;
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} rmt_led_strip_encoder_t;
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static size_t rmt_encode_led_strip(rmt_encoder_t *encoder, rmt_channel_handle_t channel, const void *primary_data, size_t data_size, rmt_encode_state_t *ret_state)
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{
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rmt_led_strip_encoder_t *led_encoder = __containerof(encoder, rmt_led_strip_encoder_t, base);
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rmt_encoder_handle_t bytes_encoder = led_encoder->bytes_encoder;
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rmt_encoder_handle_t copy_encoder = led_encoder->copy_encoder;
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rmt_encode_state_t session_state = RMT_ENCODING_RESET;
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rmt_encode_state_t state = RMT_ENCODING_RESET;
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size_t encoded_symbols = 0;
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switch (led_encoder->state) {
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case 0: // send RGB data
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encoded_symbols += bytes_encoder->encode(bytes_encoder, channel, primary_data, data_size, &session_state);
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if (session_state & RMT_ENCODING_COMPLETE) {
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led_encoder->state = 1; // switch to next state when current encoding session finished
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}
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if (session_state & RMT_ENCODING_MEM_FULL) {
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state |= RMT_ENCODING_MEM_FULL;
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goto out; // yield if there's no free space for encoding artifacts
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}
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// fall-through
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case 1: // send reset code
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encoded_symbols += copy_encoder->encode(copy_encoder, channel, &led_encoder->reset_code,
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sizeof(led_encoder->reset_code), &session_state);
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if (session_state & RMT_ENCODING_COMPLETE) {
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led_encoder->state = RMT_ENCODING_RESET; // back to the initial encoding session
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state |= RMT_ENCODING_COMPLETE;
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}
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if (session_state & RMT_ENCODING_MEM_FULL) {
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state |= RMT_ENCODING_MEM_FULL;
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goto out; // yield if there's no free space for encoding artifacts
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}
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}
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out:
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*ret_state = state;
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return encoded_symbols;
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}
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static esp_err_t rmt_del_led_strip_encoder(rmt_encoder_t *encoder)
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{
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rmt_led_strip_encoder_t *led_encoder = __containerof(encoder, rmt_led_strip_encoder_t, base);
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rmt_del_encoder(led_encoder->bytes_encoder);
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rmt_del_encoder(led_encoder->copy_encoder);
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free(led_encoder);
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return ESP_OK;
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}
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static esp_err_t rmt_led_strip_encoder_reset(rmt_encoder_t *encoder)
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{
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rmt_led_strip_encoder_t *led_encoder = __containerof(encoder, rmt_led_strip_encoder_t, base);
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rmt_encoder_reset(led_encoder->bytes_encoder);
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rmt_encoder_reset(led_encoder->copy_encoder);
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led_encoder->state = RMT_ENCODING_RESET;
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return ESP_OK;
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}
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esp_err_t rmt_new_led_strip_encoder(const led_strip_encoder_config_t *config, rmt_encoder_handle_t *ret_encoder)
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{
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esp_err_t ret = ESP_OK;
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rmt_led_strip_encoder_t *led_encoder = NULL;
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ESP_GOTO_ON_FALSE(config && ret_encoder, ESP_ERR_INVALID_ARG, err, TAG, "invalid argument");
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led_encoder = rmt_alloc_encoder_mem(sizeof(rmt_led_strip_encoder_t));
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ESP_GOTO_ON_FALSE(led_encoder, ESP_ERR_NO_MEM, err, TAG, "no mem for led strip encoder");
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led_encoder->base.encode = rmt_encode_led_strip;
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led_encoder->base.del = rmt_del_led_strip_encoder;
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led_encoder->base.reset = rmt_led_strip_encoder_reset;
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// different led strip might have its own timing requirements, following parameter is for WS2812
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rmt_bytes_encoder_config_t bytes_encoder_config = {
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.bit0 = {
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.level0 = 1,
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.duration0 = 0.3 * config->resolution / 1000000, // T0H=0.3us
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.level1 = 0,
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.duration1 = 0.9 * config->resolution / 1000000, // T0L=0.9us
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},
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.bit1 = {
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.level0 = 1,
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.duration0 = 0.9 * config->resolution / 1000000, // T1H=0.9us
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.level1 = 0,
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.duration1 = 0.3 * config->resolution / 1000000, // T1L=0.3us
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},
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.flags.msb_first = 1 // WS2812 transfer bit order: G7...G0R7...R0B7...B0
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};
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ESP_GOTO_ON_ERROR(rmt_new_bytes_encoder(&bytes_encoder_config, &led_encoder->bytes_encoder), err, TAG, "create bytes encoder failed");
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rmt_copy_encoder_config_t copy_encoder_config = {};
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ESP_GOTO_ON_ERROR(rmt_new_copy_encoder(&copy_encoder_config, &led_encoder->copy_encoder), err, TAG, "create copy encoder failed");
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uint32_t reset_ticks = config->resolution / 1000000 * 50 / 2; // reset code duration defaults to 50us
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led_encoder->reset_code = (rmt_symbol_word_t) {
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.level0 = 0,
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.duration0 = reset_ticks,
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.level1 = 0,
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.duration1 = reset_ticks,
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};
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*ret_encoder = &led_encoder->base;
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return ESP_OK;
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err:
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if (led_encoder) {
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if (led_encoder->bytes_encoder) {
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rmt_del_encoder(led_encoder->bytes_encoder);
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}
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if (led_encoder->copy_encoder) {
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rmt_del_encoder(led_encoder->copy_encoder);
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}
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free(led_encoder);
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}
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return ret;
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}

‎samples/drivers/misc/espressif_rmt/src/led_strip_encoder.h‎

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/*
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* SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#pragma once
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#include <stdint.h>
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#include <zephyr/drivers/misc/espressif_rmt/rmt_encoder.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* @brief Type of led strip encoder configuration
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*/
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typedef struct {
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uint32_t resolution; /*!< Encoder resolution, in Hz */
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} led_strip_encoder_config_t;
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/**
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* @brief Create RMT encoder for encoding LED strip pixels into RMT symbols
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*
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* @param[in] dev Pointer to the device structure for the driver instance
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* @param[in] config Encoder configuration
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* @param[out] ret_encoder Returned encoder handle
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* @return
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* - ESP_ERR_INVALID_ARG for any invalid arguments
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* - ESP_ERR_NO_MEM out of memory when creating led strip encoder
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* - ESP_OK if creating encoder successfully
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*/
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esp_err_t rmt_new_led_strip_encoder(const led_strip_encoder_config_t *config, rmt_encoder_handle_t *ret_encoder);
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#ifdef __cplusplus
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}
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#endif

‎samples/drivers/misc/espressif_rmt/src/main.c‎

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/*
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* Copyright (c) 2025 Joel Guittet (joelguittet@gmail.com)
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <zephyr/kernel.h>
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#include <zephyr/sys/printk.h>
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#include <zephyr/drivers/gpio.h>
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#include <zephyr/drivers/misc/espressif_rmt/rmt_tx.h>
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#include "led_strip_encoder.h"
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#define ZEPHYR_USER_NODE DT_PATH(zephyr_user)
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#if DT_NODE_HAS_PROP(ZEPHYR_USER_NODE, rmt_output_gpios)
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const struct gpio_dt_spec rmt_gpio = GPIO_DT_SPEC_GET(DT_PATH(zephyr_user), rmt_output_gpios);
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#else
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#error "Unsupported board: see README and check /zephyr,user node"
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#endif
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static const struct device *const rmt_dev = DEVICE_DT_GET_ONE(espressif_esp32_rmt);
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#define RMT_LED_STRIP_RESOLUTION_HZ 10000000 // 10MHz resolution, 1 tick = 0.1us (led strip needs a high resolution)
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#define EXAMPLE_LED_NUMBERS 24
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#define EXAMPLE_CHASE_SPEED_MS 10
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static uint8_t led_strip_pixels[EXAMPLE_LED_NUMBERS * 3];
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/**
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* @brief Simple helper function, converting HSV color space to RGB color space
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*
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* Wiki: https://en.wikipedia.org/wiki/HSL_and_HSV
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*
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*/
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void led_strip_hsv2rgb(uint32_t h, uint32_t s, uint32_t v, uint32_t *r, uint32_t *g, uint32_t *b)
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{
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h %= 360; // h -> [0,360]
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uint32_t rgb_max = v * 2.55f;
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uint32_t rgb_min = rgb_max * (100 - s) / 100.0f;
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uint32_t i = h / 60;
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uint32_t diff = h % 60;
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// RGB adjustment amount by hue
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uint32_t rgb_adj = (rgb_max - rgb_min) * diff / 60;
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switch (i) {
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case 0:
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*r = rgb_max;
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*g = rgb_min + rgb_adj;
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*b = rgb_min;
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break;
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case 1:
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*r = rgb_max - rgb_adj;
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*g = rgb_max;
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*b = rgb_min;
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break;
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case 2:
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*r = rgb_min;
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*g = rgb_max;
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*b = rgb_min + rgb_adj;
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break;
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case 3:
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*r = rgb_min;
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*g = rgb_max - rgb_adj;
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*b = rgb_max;
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break;
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case 4:
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*r = rgb_min + rgb_adj;
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*g = rgb_min;
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*b = rgb_max;
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break;
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default:
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*r = rgb_max;
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*g = rgb_min;
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*b = rgb_max - rgb_adj;
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break;
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}
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}
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int main(void)
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{
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uint32_t red = 0;
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uint32_t green = 0;
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uint32_t blue = 0;
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uint16_t hue = 0;
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uint16_t start_rgb = 0;
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if (!device_is_ready(rmt_dev)) {
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printk("RMT device %s is not ready\n", rmt_dev->name);
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return 0;
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}
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printk("Create RMT TX channel\n");
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rmt_channel_handle_t led_chan = NULL;
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rmt_tx_channel_config_t tx_chan_config = {
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.clk_src = RMT_CLK_SRC_DEFAULT, // select source clock
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.gpio_num = rmt_gpio.pin,
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.mem_block_symbols = 64, // increase the block size can make the LED less flickering
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.resolution_hz = RMT_LED_STRIP_RESOLUTION_HZ,
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.trans_queue_depth = 4, // set the number of transactions that can be pending in the background
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};
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ESP_ERROR_CHECK(rmt_new_tx_channel(&tx_chan_config, &led_chan));
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printk("Install led strip encoder\n");
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rmt_encoder_handle_t led_encoder = NULL;
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led_strip_encoder_config_t encoder_config = {
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.resolution = RMT_LED_STRIP_RESOLUTION_HZ,
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};
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ESP_ERROR_CHECK(rmt_new_led_strip_encoder(&encoder_config, &led_encoder));
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printk("Enable RMT TX channel\n");
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ESP_ERROR_CHECK(rmt_enable(led_chan));
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printk("Start LED rainbow chase\n");
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rmt_transmit_config_t tx_config = {
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.loop_count = 0, // no transfer loop
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};
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while (1) {
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for (int i = 0; i < 3; i++) {
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for (int j = i; j < EXAMPLE_LED_NUMBERS; j += 3) {
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// Build RGB pixels
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hue = j * 360 / EXAMPLE_LED_NUMBERS + start_rgb;
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led_strip_hsv2rgb(hue, 100, 100, &red, &green, &blue);
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led_strip_pixels[j * 3 + 0] = green;
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led_strip_pixels[j * 3 + 1] = blue;
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led_strip_pixels[j * 3 + 2] = red;
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}
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// Flush RGB values to LEDs
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ESP_ERROR_CHECK(rmt_transmit(led_chan, led_encoder, led_strip_pixels, sizeof(led_strip_pixels), &tx_config));
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ESP_ERROR_CHECK(rmt_tx_wait_all_done(led_chan, K_FOREVER));
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k_sleep(K_MSEC(EXAMPLE_CHASE_SPEED_MS));
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memset(led_strip_pixels, 0, sizeof(led_strip_pixels));
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ESP_ERROR_CHECK(rmt_transmit(led_chan, led_encoder, led_strip_pixels, sizeof(led_strip_pixels), &tx_config));
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ESP_ERROR_CHECK(rmt_tx_wait_all_done(led_chan, K_FOREVER));
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k_sleep(K_MSEC(EXAMPLE_CHASE_SPEED_MS));
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}
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start_rgb += 60;
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}
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}

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