Added modbus lib and test

software/modbus_test/.gitignore

@@ -0,0 +1 @@
+build

software/modbus_test/.vscode/c_cpp_properties.json

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+{
+    "configurations": [
+        {
+            "name": "Win32",
+            "includePath": [
+                "${workspaceFolder}/**"
+            ],
+            "defines": [
+                "_DEBUG",
+                "UNICODE",
+                "_UNICODE"
+            ]
+        }
+    ],
+    "version": 4
+}

software/modbus_test/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+list(APPEND BOARD_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/..)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(hello_world)
+
+target_sources(app PRIVATE src/main.c)
+target_sources(app PRIVATE ../lib/modbus.c)
+target_include_directories(app PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}/../lib
+)

software/modbus_test/boards/nucleo_f103rb.overlay

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+&usart1 {
+	status = "okay";
+	current-speed = <9600>;
+	modbus0 {
+		compatible = "zephyr,modbus-serial";
+		status = "okay";
+		// de-gpios = <&arduino_header 15 GPIO_ACTIVE_LOW>;	/* D9 */
+	};
+};

software/modbus_test/prj.conf

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+CONFIG_LOG=y
+CONFIG_LOG_DEFAULT_LEVEL=3
+CONFIG_CBPRINTF_FP_SUPPORT=y
+
+CONFIG_UART_CONSOLE=y # Console on USART1
+#CONFIG_RTT_CONSOLE=y
+#CONFIG_USE_SEGGER_RTT=y
+
+CONFIG_UART_INTERRUPT_DRIVEN=y
+CONFIG_UART_LINE_CTRL=n
+
+CONFIG_MODBUS=y
+CONFIG_MODBUS_ROLE_CLIENT=y

software/modbus_test/src/main.c

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+/* Testing MODBUS functionality
+   This code initializes a Modbus client, sets minimum and maximum water levels,
+   reads the current water level, and logs the results.
+   You can set the zero point and the 2m point for water level in lines 32 and 38.
+*/
+#include <zephyr/logging/log.h>
+#include <zephyr/kernel.h>
+#include <zephyr/drivers/gpio.h>
+
+#include "modbus.h"
+
+LOG_MODULE_REGISTER(main, CONFIG_LOG_DEFAULT_LEVEL);
+
+/* 1000 msec = 1 sec */
+#define SLEEP_TIME_MS 1000
+
+int main(void)
+{
+	int rc;
+
+	rc = mb_init_client();
+	if (rc != 0)
+	{
+		LOG_ERR("Failed to initialize Modbus client: %d", rc);
+		return rc;
+	}
+	LOG_INF("Modbus client initialized successfully");
+
+	double water_level = 0.0;
+	int water_level_mm, water_level_min_mm, water_level_max_mm = 0;
+
+	rc = mb_write_minimum_mm(42); // Set the zero point for water level
+	if (rc < 0)
+	{
+		LOG_ERR("Failed to write minimum water level: %d", rc);
+		return rc;
+	}
+	rc = mb_write_maximum_mm(2000); // Set the 2m point for water level
+	if (rc < 0)
+	{
+		LOG_ERR("Failed to write maximum water level: %d", rc);
+		return rc;
+	}
+	rc = mb_read_minimum_mm(&water_level_min_mm);
+	if (rc < 0)
+	{
+		LOG_ERR("Failed to read minimum water level: %d", rc);
+		return rc;
+	}
+	rc = mb_read_maximum_mm(&water_level_max_mm);
+	if (rc < 0)
+	{
+		LOG_ERR("Failed to read maximum water level: %d", rc);
+		return rc;
+	}
+	LOG_INF("Water zero point is set to: %dmm", water_level_min_mm);
+	LOG_INF("Water 2m point is set to: %dmm", water_level_max_mm);
+
+	while (1)
+	{ /* Read water level */
+		rc = mb_read_water_level(&water_level);
+		if (rc < 0)
+		{
+			LOG_ERR("Failed to read water level: %d", rc);
+			return rc;
+		}
+		rc = mb_read_water_level_mm(&water_level_mm);
+		if (rc < 0)
+		{
+			LOG_ERR("Failed to read water level: %d", rc);
+			return rc;
+		}
+		LOG_INF("Water level: %.3fm", water_level);
+		LOG_INF("Water level: %dmm", water_level_mm);
+		LOG_INF("Modbus test completed successfully");
+		return 0;
+		k_sleep(K_SECONDS(1));
+	}
+
+	return 0;
+}