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samples: uart: async_api: added
Add a sample that utilises the ASYNC API to queue packets in bursts. Signed-off-by: Jordan Yates <[email protected]>
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‎samples/drivers/uart/async_api/CMakeLists.txt

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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(uart_async_api)
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target_sources(app PRIVATE src/main.c)

‎samples/drivers/uart/async_api/README.rst

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.. zephyr:code-sample:: uart_async
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:name: UART ASYNC API
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:relevant-api: uart_interface
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Demonstrate the use of the asynchronous API
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Overview
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********
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This sample demonstrates how to use the UART serial driver asynchronous
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API through a simple packet transmitter.
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Every 5 seconds, 1 to 4 data payloads are generated and queued for
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transmission. Every other 5 second period, receiving is enabled through
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the asynchronous API.
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By default, the UART peripheral that is normally used for the Zephyr shell
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is used, so that almost every board should be supported.
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Building and Running
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********************
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Build and flash the sample as follows, changing ``nrf52840dk/nrf52840`` for
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your board:
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.. zephyr-app-commands::
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:zephyr-app: samples/drivers/uart/async_api
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:board: nrf52840dk/nrf52840
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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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Loop 0: Packet: 0
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Loop 0: Packet: 1
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Loop 0: Packet: 2
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[00:00:05.001,919] <inf> sample: Loop 0: Sending 3 packets
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[00:00:05.002,008] <inf> sample: RX is now enabled
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Loop 1: Packet: 0
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[00:00:10.002,086] <inf> sample: Loop 1: Sending 1 packets
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[00:00:10.002,138] <inf> sample: RX is now disabled
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Loop 2: Packet: 0
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Loop 2: Packet: 1
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[00:00:15.002,215] <inf> sample: Loop 2: Sending 2 packets
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[00:00:15.002,293] <inf> sample: RX is now enabled
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[00:00:15.009,010] <inf> sample: RX_RDY
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68 65 6c 6c 6f 0a |hello.
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Loop 3: Packet: 0
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Loop 3: Packet: 1
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Loop 3: Packet: 2
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[00:00:20.002,343] <inf> sample: Loop 3: Sending 3 packets
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[00:00:20.002,424] <inf> sample: RX is now disabled
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Note that because the UART transmissions are triggered directly, they will
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appear in the serial logs **before** the ``LOG_INF`` message at the top of
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the loop, since log writes are typically deferred by several seconds

‎samples/drivers/uart/async_api/prj.conf

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CONFIG_LOG=y
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CONFIG_NET_BUF=y
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CONFIG_SERIAL=y
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CONFIG_UART_ASYNC_API=y
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CONFIG_TEST_RANDOM_GENERATOR=y

‎samples/drivers/uart/async_api/sample.yaml

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sample:
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name: UART ASYNC API driver sample
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tests:
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sample.drivers.uart.async_api:
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integration_platforms:
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- nrf52840dk/nrf52840
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tags:
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- serial
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- uart
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filter: CONFIG_SERIAL and
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CONFIG_UART_ASYNC_API and
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dt_chosen_enabled("zephyr,shell-uart")
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harness: keyboard

‎samples/drivers/uart/async_api/src/main.c

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/*
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* Copyright (c) 2025 Embeint Inc
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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/device.h>
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#include <zephyr/net_buf.h>
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#include <zephyr/logging/log.h>
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#include <zephyr/drivers/uart.h>
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#include <zephyr/random/random.h>
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/* change this to any other UART peripheral if desired */
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#define UART_DEVICE_NODE DT_CHOSEN(zephyr_shell_uart)
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/* Maximum number of packets to generate per iteration */
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#define LOOP_ITER_MAX_TX 4
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/* Maximum size of our TX packets */
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#define MAX_TX_LEN 32
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#define RX_CHUNK_LEN 32
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/* Buffer pool for our TX payloads */
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NET_BUF_POOL_DEFINE(tx_pool, LOOP_ITER_MAX_TX, MAX_TX_LEN, 0, NULL);
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struct k_fifo tx_queue;
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struct net_buf *tx_pending_buffer;
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uint8_t async_rx_buffer[2][RX_CHUNK_LEN];
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volatile uint8_t async_rx_buffer_idx;
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static const struct device *const uart_dev = DEVICE_DT_GET(UART_DEVICE_NODE);
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LOG_MODULE_REGISTER(sample, LOG_LEVEL_INF);
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static void uart_callback(const struct device *dev, struct uart_event *evt, void *user_data)
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{
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struct net_buf *buf;
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int rc;
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LOG_DBG("EVENT: %d", evt->type);
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switch (evt->type) {
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case UART_TX_DONE:
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LOG_DBG("TX complete %p", tx_pending_buffer);
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/* Free TX buffer */
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net_buf_unref(tx_pending_buffer);
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tx_pending_buffer = NULL;
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/* Handle any queued buffers */
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buf = k_fifo_get(&tx_queue, K_NO_WAIT);
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if (buf != NULL) {
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rc = uart_tx(dev, buf->data, buf->len, 0);
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if (rc != 0) {
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LOG_ERR("TX from ISR failed (%d)", rc);
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net_buf_unref(buf);
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} else {
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tx_pending_buffer = buf;
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}
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}
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break;
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case UART_RX_BUF_REQUEST:
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/* Return the next buffer index */
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LOG_DBG("Providing buffer index %d", async_rx_buffer_idx);
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rc = uart_rx_buf_rsp(dev, async_rx_buffer[async_rx_buffer_idx],
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sizeof(async_rx_buffer[0]));
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__ASSERT_NO_MSG(rc == 0);
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async_rx_buffer_idx = async_rx_buffer_idx ? 0 : 1;
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break;
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case UART_RX_BUF_RELEASED:
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case UART_RX_DISABLED:
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break;
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case UART_RX_RDY:
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LOG_HEXDUMP_INF(evt->data.rx.buf + evt->data.rx.offset,
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evt->data.rx.len, "RX_RDY");
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break;
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default:
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LOG_WRN("Unhandled event %d", evt->type);
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}
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}
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int main(void)
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{
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bool rx_enabled = false;
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struct net_buf *tx_buf;
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int loop_counter = 0;
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uint8_t num_tx;
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int tx_len;
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int rc;
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/* Register the async interrupt handler */
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uart_callback_set(uart_dev, uart_callback, (void *)uart_dev);
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while (1) {
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/* Wait a while until the next burst transmission */
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k_sleep(K_SECONDS(5));
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/* Each loop, try to send a random number of packets */
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num_tx = (sys_rand32_get() % LOOP_ITER_MAX_TX) + 1;
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LOG_INF("Loop %d: Sending %d packets", loop_counter, num_tx);
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for (int i = 0; i < num_tx; i++) {
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/* Allocate the data packet */
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tx_buf = net_buf_alloc(&tx_pool, K_FOREVER);
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/* Populate it with data */
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tx_len = snprintk(tx_buf->data, net_buf_tailroom(tx_buf),
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"Loop %d: Packet: %d\r\n", loop_counter, i);
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net_buf_add(tx_buf, tx_len);
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/* Queue packet for transmission */
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rc = uart_tx(uart_dev, tx_buf->data, tx_buf->len, SYS_FOREVER_US);
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if (rc == 0) {
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/* Store the pending buffer */
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tx_pending_buffer = tx_buf;
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} else if (rc == -EBUSY) {
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/* Transmission is already in progress */
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LOG_DBG("Queuing buffer %p", tx_buf);
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k_fifo_put(&tx_queue, tx_buf);
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} else {
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LOG_ERR("Unknown error (%d)", rc);
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}
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}
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/* Toggle the RX state */
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if (rx_enabled) {
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uart_rx_disable(uart_dev);
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} else {
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async_rx_buffer_idx = 1;
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uart_rx_enable(uart_dev, async_rx_buffer[0], RX_CHUNK_LEN, 100);
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}
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rx_enabled = !rx_enabled;
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LOG_INF("RX is now %s", rx_enabled ? "enabled" : "disabled");
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loop_counter += 1;
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}
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}

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