samples: add Modbus RTU client sample

Add Modbus RTU client sample.

Signed-off-by: Johann Fischer <j.fischer@phytec.de>

samples/subsys/modbus/rtu_client/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.13.1)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(modbus-rtu-client)
+
+target_sources(app PRIVATE src/main.c)

samples/subsys/modbus/rtu_client/README.rst

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+.. _modbus-rtu-client-sample:
+
+Modbus RTU Client Sample
+########################
+
+Overview
+********
+
+This is a simple application demonstrating a Modbus RTU client implementation
+in Zephyr RTOS.
+
+Requirements
+************
+
+This sample has been tested with the nRF52840-DK and FRDM-K64F boards,
+but it should work with any board that has a free UART interface.
+
+RTU client example is running on an evaluation board and communicates
+with another board that has been prepared according to the description
+`modbus-rtu-server-sample`.
+
+In addition to the evaluation board, an USB to RS-485 bus adapter and
+a RS-485 shield are required. Shield converts the UART TX, RX signals to
+RS-485 and does not need a specific overlay, an Arduino header compatible
+shield like `joy-it RS-485 shield for Arduino`_ can be used.
+
+The A+, B- lines of the RS-485 shield should be connected together.
+
+Alternatively UART RX,TX signals of two boards can be connected crosswise.
+
+Building and Running
+********************
+
+This sample can be found under
+:zephyr_file:`samples/subsys/modbus/rtu_client` in the Zephyr tree.
+
+The following commands build and flash RTU client sample.
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/subsys/modbus/rtu_client
+   :board: frdm_k64f
+   :goals: build flash
+   :compact:
+
+The example communicates with the RTU server and lets the LEDs light up
+one after the other.
+
+.. code-block:: console
+
+   *** Booting Zephyr OS build zephyr-v2.3.0-1993-g07e8d80ae028  ***
+   [00:00:00.005,000] <inf> mb_rtu: RTU timeout 2005 us
+   [00:00:00.050,000] <inf> mbc_sample: WR|RD holding register:
+   48 00 65 00 6c 00 6c 00  6f 00 00 00 00 00 00 00 |H.e.l.l. o.......
+   [00:00:00.062,000] <inf> mbc_sample: Coils state 0x00
+   [00:00:00.864,000] <inf> mbc_sample: Coils state 0x07
+
+
+.. _`joy-it RS-485 shield for Arduino`: https://joy-it.net/en/products/ARD-RS485

samples/subsys/modbus/rtu_client/app.overlay

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+/*
+ * Copyright (c) 2020 Phytec Messtechnik GmbH
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&arduino_serial {
+	status = "okay";
+
+	modbus0 {
+		compatible = "zephyr,modbus-serial";
+		label = "MODBUS";
+		status = "okay";
+	};
+};

samples/subsys/modbus/rtu_client/prj.conf

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+CONFIG_LOG=y
+CONFIG_GPIO=y
+CONFIG_SERIAL=y
+CONFIG_UART_INTERRUPT_DRIVEN=y
+CONFIG_UART_LINE_CTRL=n
+
+CONFIG_MODBUS_RTU=y
+CONFIG_MODBUS_RTU_ROLE_CLIENT=y

samples/subsys/modbus/rtu_client/sample.yaml

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+sample:
+  name: Modbus RTU Client Sample
+tests:
+  sample.modbus.rtu_client:
+    tags: uart modbus
+    depends_on: gpio, arduino_serial

samples/subsys/modbus/rtu_client/src/main.c

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+/*
+ * Copyright (c) 2020 PHYTEC Messtechnik GmbH
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr.h>
+#include <sys/util.h>
+#include <drivers/gpio.h>
+#include <modbus/modbus_rtu.h>
+
+#include <logging/log.h>
+LOG_MODULE_REGISTER(mbc_sample, LOG_LEVEL_INF);
+
+#define RTU_IFACE	0
+
+static int init_modbus_client(void)
+{
+	const uint32_t mb_rtu_br = 19200;
+	const uint32_t rsp_timeout = 50000;
+
+	return mb_rtu_cfg_client(RTU_IFACE, mb_rtu_br, UART_CFG_PARITY_NONE,
+				 rsp_timeout, false);
+}
+
+void main(void)
+{
+	uint16_t holding_reg[8] = {'H', 'e', 'l', 'l', 'o'};
+	const uint8_t coil_qty = 3;
+	uint8_t coil[1] = {0};
+	const int32_t sleep = 250;
+	static uint8_t node = 1;
+	int err;
+
+
+	if (init_modbus_client()) {
+		LOG_ERR("Modbus RTU client initialization failed");
+		return;
+	}
+
+	err = mb_rtu_write_holding_regs(RTU_IFACE, node, 0, holding_reg,
+					ARRAY_SIZE(holding_reg));
+	if (err != 0) {
+		LOG_ERR("FC16 failed");
+		return;
+	}
+
+	err = mb_rtu_read_holding_regs(RTU_IFACE, node, 0, holding_reg,
+				       ARRAY_SIZE(holding_reg));
+	if (err != 0) {
+		LOG_ERR("FC03 failed with %d", err);
+		return;
+	}
+
+	LOG_HEXDUMP_INF(holding_reg, sizeof(holding_reg),
+			"WR|RD holding register:");
+
+	while (true) {
+		uint16_t addr = 0;
+
+		err = mb_rtu_read_coils(RTU_IFACE, node, 0, coil, coil_qty);
+		if (err != 0) {
+			LOG_ERR("FC01 failed with %d", err);
+			return;
+		}
+
+		LOG_INF("Coils state 0x%02x", coil[0]);
+
+		err = mb_rtu_write_coil(RTU_IFACE, node, addr++, true);
+		if (err != 0) {
+			LOG_ERR("FC05 failed with %d", err);
+			return;
+		}
+
+		k_msleep(sleep);
+		err = mb_rtu_write_coil(RTU_IFACE, node, addr++, true);
+		if (err != 0) {
+			LOG_ERR("FC05 failed with %d", err);
+			return;
+		}
+
+		k_msleep(sleep);
+		err = mb_rtu_write_coil(RTU_IFACE, node, addr++, true);
+		if (err != 0) {
+			LOG_ERR("FC05 failed with %d", err);
+			return;
+		}
+
+		k_msleep(sleep);
+		err = mb_rtu_read_coils(RTU_IFACE, node, 0, coil, coil_qty);
+		if (err != 0) {
+			LOG_ERR("FC01 failed with %d", err);
+			return;
+		}
+
+		LOG_INF("Coils state 0x%02x", coil[0]);
+
+		coil[0] = 0;
+		err = mb_rtu_write_coils(RTU_IFACE, node, 0, coil, coil_qty);
+		if (err != 0) {
+			LOG_ERR("FC15 failed with %d", err);
+			return;
+		}
+
+		k_msleep(sleep);
+	}
+}