example: add nmea0183 parser example

Add NMEA0183 Parser example to illustrate how to use uart event driver together with esp event library to get GPS information.

examples/peripherals/uart/uart_echo_rs485/main/rs485_example.c

@@ -0,0 +1,126 @@
+/* Uart Events Example
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "esp_system.h"
+#include "nvs_flash.h"
+#include "driver/uart.h"
+#include "freertos/queue.h"
+#include "esp_log.h"
+#include "soc/uart_struct.h"
+
+/**
+ * This is a example example which echos any data it receives on UART back to the sender.
+ *
+ * - port: UART2
+ * - rx buffer: on
+ * - tx buffer: off
+ * - flow control: off
+ *
+ * This example has been tested on a 3 node RS485 Serial Bus
+ * 
+ */
+
+// Note: UART2 default pins IO16, IO17 do not work on ESP32-WROVER module 
+// because these pins connected to PSRAM
+#define ECHO_TEST_TXD   (23)
+#define ECHO_TEST_RXD   (22)
+
+// RTS for RS485 Half-Duplex Mode manages DE/~RE
+#define ECHO_TEST_RTS   (18)
+
+// CTS is not used in RS485 Half-Duplex Mode
+#define ECHO_TEST_CTS  UART_PIN_NO_CHANGE
+
+#define BUF_SIZE        (127)
+#define BAUD_RATE       (115200)
+
+// Read packet timeout
+#define PACKET_READ_TICS        (100 / portTICK_RATE_MS)
+#define ECHO_TASK_STACK_SIZE    (2048)
+#define ECHO_TASK_PRIO          (10)
+#define ECHO_UART_PORT          (UART_NUM_2)
+
+static const char *TAG = "RS485_ECHO_APP";
+
+// An example of echo test with hardware flow control on UART
+static void echo_task()
+{
+    const int uart_num = ECHO_UART_PORT;
+    uart_config_t uart_config = {
+        .baud_rate = BAUD_RATE,
+        .data_bits = UART_DATA_8_BITS,
+        .parity = UART_PARITY_DISABLE,
+        .stop_bits = UART_STOP_BITS_1,
+        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
+        .rx_flow_ctrl_thresh = 122,
+    };
+    
+    // Set UART log level
+    esp_log_level_set(TAG, ESP_LOG_INFO);
+    
+    ESP_LOGI(TAG, "Start RS485 application test and configure UART.");
+
+    // Configure UART parameters
+    uart_param_config(uart_num, &uart_config);
+    
+    ESP_LOGI(TAG, "UART set pins, mode and install driver.");
+    // Set UART1 pins(TX: IO23, RX: I022, RTS: IO18, CTS: IO19)
+    uart_set_pin(uart_num, ECHO_TEST_TXD, ECHO_TEST_RXD, ECHO_TEST_RTS, ECHO_TEST_CTS);
+
+    // Install UART driver (we don't need an event queue here)
+    // In this example we don't even use a buffer for sending data.
+    uart_driver_install(uart_num, BUF_SIZE * 2, 0, 0, NULL, 0);
+
+    // Set RS485 half duplex mode
+    uart_set_mode(uart_num, UART_MODE_RS485_HALF_DUPLEX);
+
+    // Allocate buffers for UART
+    uint8_t* data = (uint8_t*) malloc(BUF_SIZE);
+
+    ESP_LOGI(TAG, "UART start recieve loop.\r\n");
+    uart_write_bytes(uart_num, "Start RS485 UART test.\r\n", 24);
+
+    while(1) {
+        //Read data from UART
+        int len = uart_read_bytes(uart_num, data, BUF_SIZE, PACKET_READ_TICS);
+        
+        //Write data back to UART
+        if (len > 0) {
+            uart_write_bytes(uart_num, "\r\n", 2);
+            char prefix[] = "RS485 Received: [";
+            uart_write_bytes(uart_num, prefix, (sizeof(prefix) - 1));
+            
+            ESP_LOGI(TAG, "Received %u bytes:", len);
+            printf("[ ");
+            for (int i = 0; i < len; i++) {
+                printf("0x%.2X ", (uint8_t)data[i]);
+                uart_write_bytes(uart_num, (const char*)&data[i], 1);
+                // Add a Newline character if you get a return charater from paste (Paste tests multibyte receipt/buffer)
+                if (data[i] == '\r') {
+                    uart_write_bytes(uart_num, "\n", 1);
+                }
+            }
+            printf("] \n");
+            uart_write_bytes(uart_num, "]\r\n", 3);
+        } else {
+            // Echo a "." to show we are alive while we wait for input
+            uart_write_bytes(uart_num, ".", 1);
+        }
+    }
+}
+
+void app_main()
+{
+    //A uart read/write example without event queue;
+    xTaskCreate(echo_task, "uart_echo_task", ECHO_TASK_STACK_SIZE, NULL, ECHO_TASK_PRIO, NULL);
+}