samples: boards: espressif: ulp: Add Echo Sample

Add an echo sample based on polling API from UART.

Signed-off-by: Lucas Tamborrino <lucas.tamborrino@espressif.com>

Author: LucasTambor

samples/boards/espressif/ulp/lp_core/echo_ulp/CMakeLists.txt

@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+set(REMOTE_ZEPHYR_DIR ${CMAKE_CURRENT_BINARY_DIR}/../echo_ulp_lpcore/zephyr)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+
+message(STATUS "${CONFIG_BOARD_TARGET} compile as Master in this sample")
+project(echo_ulp_hpcore)
+
+target_sources(app PRIVATE src/main.c)

samples/boards/espressif/ulp/lp_core/echo_ulp/Kconfig.sysbuild

@@ -0,0 +1,8 @@
+# Copyright (c) 2025 Espressif Systems (Shanghai) Co., Ltd.
+# SPDX-License-Identifier: Apache-2.0
+
+source "share/sysbuild/Kconfig"
+
+config ULP_REMOTE_BOARD
+	string
+	default "esp32c6_devkitc/esp32c6/lpcore" if $(BOARD) = "esp32c6_devkitc"

samples/boards/espressif/ulp/lp_core/echo_ulp/README.rst

@@ -0,0 +1,39 @@
+.. zephyr:code-sample:: echo-ulp
+   :name: Echo ULP
+
+   Leverage Zephyr's UART API to use the LP UART on the ESP32-C6's LP core.
+
+Overview
+********
+
+This sample application demonstrates how to use poll-based APIs from the Zephyr
+UART driver subsystem. It reads characters from the LP UART using
+:c:func:`uart_poll_in` and echoes them back using :c:func:`uart_poll_out`.
+
+Building and Flashing
+*********************
+
+Build the sample code as follows:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/boards/espressif/ulp/lp_core/echo_ulp
+   :board: esp32c6_devkitc/esp32c6/hpcore
+   :west-args: --sysbuild
+   :goals: build
+   :compact:
+
+Flash it to the device with the command:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/boards/espressif/ulp/lp_core/echo_ulp
+   :board: esp32c6_devkitc/esp32c6/hpcore
+   :west-args: --sysbuild
+   :goals: flash
+   :compact:
+
+Sample Output
+=============
+
+.. code-block:: console
+
+    UART echo example started. Type something...

samples/boards/espressif/ulp/lp_core/echo_ulp/app.overlay

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2025 Espressif Systems (Shanghai) Co., Ltd.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&lp_uart {
+	status = "okay";
+};

samples/boards/espressif/ulp/lp_core/echo_ulp/prj.conf

@@ -0,0 +1 @@
+CONFIG_ULP_COPROC_ENABLED=y

samples/boards/espressif/ulp/lp_core/echo_ulp/remote/CMakeLists.txt

@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+
+message(STATUS "${BOARD} compiles as remote in this sample")
+project(echo_ulp_lpcore)
+
+target_sources(app PRIVATE src/main.c)

samples/boards/espressif/ulp/lp_core/echo_ulp/remote/prj.conf

@@ -0,0 +1,3 @@
+CONFIG_MAIN_STACK_SIZE=1024
+CONFIG_ISR_STACK_SIZE=64
+CONFIG_IDLE_STACK_SIZE=32

samples/boards/espressif/ulp/lp_core/echo_ulp/remote/src/main.c

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2025 Espressif Systems (Shanghai) Co., Ltd.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdio.h>
+#include <zephyr/device.h>
+#include <zephyr/drivers/uart.h>
+
+#define UART_DEVICE_NODE DT_NODELABEL(lp_uart)
+
+int main(void)
+{
+	const struct device *uart_dev = DEVICE_DT_GET(UART_DEVICE_NODE);
+	char c;
+	int ret = 0;
+
+	printf("UART echo example started. Type something...\n");
+
+	while (1) {
+		ret = uart_poll_in(uart_dev, &c);
+		if (ret == 0) {
+			/* Echo character back out */
+			uart_poll_out(uart_dev, c);
+			if (c == '\r') {
+				uart_poll_out(uart_dev, '\n');
+			}
+		}
+	}
+
+	return 0;
+}

samples/boards/espressif/ulp/lp_core/echo_ulp/sample.yaml

@@ -0,0 +1,9 @@
+sample:
+  name: ESP32-C6 LP_CORE Echo Sample
+tests:
+  sample.boards.espressif.ulp.lp_core.echo_ulp:
+    platform_allow:
+      - esp32c6_devkitc/esp32c6/hpcore
+    tags:
+      - samples
+    sysbuild: true

samples/boards/espressif/ulp/lp_core/echo_ulp/src/main.c

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2025 Espressif Systems (Shanghai) Co., Ltd.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdio.h>
+#include <zephyr/sys/poweroff.h>
+#include <esp_sleep.h>
+#include <ulp_lp_core.h>
+#include <zephyr/kernel.h>
+
+int main(void)
+{
+	while (1) {
+		k_sleep(K_MSEC(1000));
+	}
+
+	return 0;
+}