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samples: zbus: add ZBus multidomain UART forwarder sample
Add sample application demonstrating ZBus multidomain communication over UART between two devices. Shows practical usage of shadow channels and proxy agents for inter-domain message forwarding. The sample consists of two devices: - Device A: Acts as request publisher with master request_channel - Device B: Acts as request listener/responder with shadow request_channel Device A publishes periodic requests which are automatically forwarded via UART to Device B. Device B processes requests and sends responses back through the response_channel, demonstrating bidirectional multidomain zbus communication. Key features demonstrated: - ZBUS_MULTIDOMAIN_CHAN_DEFINE for shared conditional channel definitions - ZBUS_PROXY_AGENT_DEFINE for UART backend configuration - Shadow vs master channel behavior - Automatic message forwarding via proxy agents Signed-off-by: Trond F. Christiansen <[email protected]>
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‎samples/subsys/zbus/uart_forwarder/common/common.h‎

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#ifndef COMMON_H
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#define COMMON_H
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#include <zephyr/zbus/zbus.h>
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/* Sample data structures for request and response */
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struct request_data {
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int request_id;
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int min_value;
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int max_value;
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};
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struct response_data {
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int response_id;
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int value;
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};
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/* Conditional compilation for device-specific code, needed if channels should be included on a
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* subset of applications devices
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*/
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#if defined(ZBUS_DEVICE_A) || defined(ZBUS_DEVICE_B)
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#define include_on_device_a_b 1
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#else
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#define include_on_device_a_b 0
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#endif
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/* Define shared channels for request and response
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* request_channel is master on device A and shadow on device B
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* response_channel is shadow on device A and master on device B
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*/
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ZBUS_MULTIDOMAIN_CHAN_DEFINE(request_channel, struct request_data, NULL, NULL, ZBUS_OBSERVERS_EMPTY,
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ZBUS_MSG_INIT(0), IS_ENABLED(ZBUS_DEVICE_A), include_on_device_a_b);
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ZBUS_MULTIDOMAIN_CHAN_DEFINE(response_channel, struct response_data, NULL, NULL,
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ZBUS_OBSERVERS_EMPTY, ZBUS_MSG_INIT(0), IS_ENABLED(ZBUS_DEVICE_B),
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include_on_device_a_b);
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#endif /* COMMON_H */

‎samples/subsys/zbus/uart_forwarder/dev_a/CMakeLists.txt‎

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#
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# Copyright (c) 2025 Nordic Semiconductor ASA
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#
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# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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#
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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(zbus_uart_forwarder_dev_a)
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zephyr_library_include_directories(
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src
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../common
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)
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# Define which device this is
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zephyr_compile_definitions(ZBUS_DEVICE_A=1)
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target_sources(app PRIVATE src/main.c)

‎samples/subsys/zbus/uart_forwarder/dev_a/Kconfig‎

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#
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# Copyright (c) 2025 Nordic Semiconductor ASA
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#
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# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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#
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source "Kconfig.zephyr"

‎samples/subsys/zbus/uart_forwarder/dev_a/boards/nrf5340dk_nrf5340_cpuapp.overlay‎

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/*
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* Copyright (c) 2025 Nordic Semiconductor ASA
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*
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* SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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*/
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&uart1 {
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status = "okay";
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current-speed = <1000000>;
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/delete-property/ hw-flow-control;
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};
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&uart2 {
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compatible = "nordic,nrf-uarte";
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status = "okay";
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current-speed = <1000000>;
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pinctrl-0 = <&uart2_default>;
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pinctrl-1 = <&uart2_sleep>;
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pinctrl-names = "default", "sleep";
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/delete-property/ hw-flow-control;
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};
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&pinctrl {
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uart2_default: uart2_default {
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group1 {
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psels = <NRF_PSEL(UART_TX, 1, 7)>,
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<NRF_PSEL(UART_RTS, 0, 9)>;
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};
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group2 {
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psels = <NRF_PSEL(UART_RX, 1, 6)>,
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<NRF_PSEL(UART_CTS, 0, 8)>;
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bias-pull-up;
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};
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};
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uart2_sleep: uart2_sleep {
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group1 {
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psels = <NRF_PSEL(UART_TX, 1, 7)>,
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<NRF_PSEL(UART_RX, 1, 6)>,
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<NRF_PSEL(UART_RTS, 0, 9)>,
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<NRF_PSEL(UART_CTS, 0, 8)>;
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low-power-enable;
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};
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};
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};

‎samples/subsys/zbus/uart_forwarder/dev_a/prj.conf‎

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# Copyright (c) 2025 Nordic Semiconductor ASA
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# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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CONFIG_LOG=y
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# CONFIG_LOG_MODE_MINIMAL=y
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CONFIG_LOG_DBG_COLOR_BLUE=y
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CONFIG_SERIAL=y
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CONFIG_UART_ASYNC_API=y
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CONFIG_UART_1_NRF_ASYNC_LOW_POWER=y
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CONFIG_UART_2_NRF_ASYNC_LOW_POWER=y
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CONFIG_ZBUS=y
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CONFIG_ZBUS_MULTIDOMAIN=y
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CONFIG_ZBUS_MULTIDOMAIN_UART=y
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CONFIG_ZBUS_MULTIDOMAIN_LOG_LEVEL_INF=y

‎samples/subsys/zbus/uart_forwarder/dev_a/src/main.c‎

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/*
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* Copyright (c) 2025 Nordic Semiconductor ASA
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*
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* SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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*/
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#include <zephyr/kernel.h>
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#include <zephyr/logging/log.h>
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#include <string.h>
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#include <zephyr/zbus/zbus.h>
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#include <zephyr/zbus/multidomain/zbus_multidomain.h>
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#include "common.h"
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LOG_MODULE_REGISTER(main, LOG_LEVEL_DBG);
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/* NOTE: Shared channels request_channel and response_channel are defined in common.h */
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/* Set up proxy agent for UART1 and add response channel to be forwarded */
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ZBUS_PROXY_AGENT_DEFINE(uart1_proxy, ZBUS_MULTIDOMAIN_TYPE_UART, uart1);
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ZBUS_PROXY_ADD_CHANNEL(uart1_proxy, request_channel);
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/* Log response data coming from the response channel */
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void uart_forwarder_listener_cb(const struct zbus_channel *chan)
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{
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const struct response_data *data = zbus_chan_const_msg(chan);
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LOG_INF("Received message on channel %s", chan->name);
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LOG_INF("Response ID: %d, Value: %d", data->response_id, data->value);
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}
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ZBUS_LISTENER_DEFINE(uart_forwarder_listener, uart_forwarder_listener_cb);
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ZBUS_CHAN_ADD_OBS(response_channel, uart_forwarder_listener, 0);
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bool print_channel_info(const struct zbus_channel *chan)
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{
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if (!chan) {
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LOG_ERR("Channel is NULL");
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return false;
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}
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LOG_INF("Channel %s is a %s channel", chan->name,
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ZBUS_CHANNEL_IS_SHADOW(chan) ? "shadow" : "master");
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return true;
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}
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int main(void)
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{
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LOG_INF("ZBUS Multidomain UART Forwarder Sample Application");
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zbus_iterate_over_channels(print_channel_info);
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struct request_data data = {.request_id = 1, .min_value = -1, .max_value = 1};
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while (1) {
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int ret = zbus_chan_pub(&request_channel, &data, K_MSEC(100));
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if (ret < 0) {
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LOG_ERR("Failed to publish on channel %s: %d", request_channel.name, ret);
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} else {
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LOG_INF("Published on channel %s. Request ID=%d, Min=%d, Max=%d",
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request_channel.name, data.request_id, data.min_value,
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data.max_value);
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}
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data.request_id++;
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data.min_value -= 1;
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data.max_value += 1;
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k_sleep(K_SECONDS(5));
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}
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return 0;
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}

‎samples/subsys/zbus/uart_forwarder/dev_b/CMakeLists.txt‎

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#
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# Copyright (c) 2025 Nordic Semiconductor ASA
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#
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# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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#
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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(zbus_uart_forwarder_dev_b)
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zephyr_library_include_directories(
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src
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../common
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)
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# Define which device this is
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zephyr_compile_definitions(ZBUS_DEVICE_B=1)
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target_sources(app PRIVATE src/main.c)

‎samples/subsys/zbus/uart_forwarder/dev_b/Kconfig‎

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#
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# Copyright (c) 2025 Nordic Semiconductor ASA
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#
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# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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#
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source "Kconfig.zephyr"

‎samples/subsys/zbus/uart_forwarder/dev_b/boards/nrf5340dk_nrf5340_cpuapp.overlay‎

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/*
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* Copyright (c) 2025 Nordic Semiconductor ASA
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*
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* SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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*/
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&uart1 {
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status = "okay";
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current-speed = <1000000>;
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/delete-property/ hw-flow-control;
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};
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&uart2 {
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compatible = "nordic,nrf-uarte";
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status = "okay";
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current-speed = <1000000>;
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pinctrl-0 = <&uart2_default>;
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pinctrl-1 = <&uart2_sleep>;
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pinctrl-names = "default", "sleep";
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/delete-property/ hw-flow-control;
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};
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&pinctrl {
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uart2_default: uart2_default {
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group1 {
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psels = <NRF_PSEL(UART_TX, 1, 7)>,
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<NRF_PSEL(UART_RTS, 0, 9)>;
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};
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group2 {
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psels = <NRF_PSEL(UART_RX, 1, 6)>,
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<NRF_PSEL(UART_CTS, 0, 8)>;
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bias-pull-up;
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};
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};
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uart2_sleep: uart2_sleep {
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group1 {
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psels = <NRF_PSEL(UART_TX, 1, 7)>,
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<NRF_PSEL(UART_RX, 1, 6)>,
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<NRF_PSEL(UART_RTS, 0, 9)>,
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<NRF_PSEL(UART_CTS, 0, 8)>;
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low-power-enable;
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};
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};
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};

‎samples/subsys/zbus/uart_forwarder/dev_b/prj.conf‎

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# Copyright (c) 2025 Nordic Semiconductor ASA
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# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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CONFIG_LOG=y
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# CONFIG_LOG_MODE_MINIMAL=y
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CONFIG_LOG_DBG_COLOR_BLUE=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
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CONFIG_UART_1_NRF_ASYNC_LOW_POWER=y
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CONFIG_UART_2_NRF_ASYNC_LOW_POWER=y
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CONFIG_ZBUS=y
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CONFIG_ZBUS_MULTIDOMAIN=y
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CONFIG_ZBUS_MULTIDOMAIN_UART=y
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CONFIG_ZBUS_MULTIDOMAIN_LOG_LEVEL_INF=y

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