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_async_rxtxtasks/CMakeLists.txt

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+# The following lines of boilerplate have to be in your project's CMakeLists
+# in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(uart_async_rxtxtasks)

examples/peripherals/uart/uart_async_rxtxtasks/Makefile

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+#
+# This is a project Makefile. It is assumed the directory this Makefile resides in is a
+# project subdirectory.
+#
+
+PROJECT_NAME := uart_async_rxtxtasks
+
+include $(IDF_PATH)/make/project.mk

examples/peripherals/uart/uart_async_rxtxtasks/README.md

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+# UART Asynchronous Example with Separate Receive and Transfer Tasks
+
+(See the README.md file in the upper level 'examples' directory for more information about examples.)
+
+This example demonstrates how two asynchronous tasks can use the same UART interface for communication. One can use
+this example to develop more complex applications for serial communication.
+
+The example starts two FreeRTOS tasks:
+1. The first task periodically transmits `Hello world` via the UART.
+2. The second task task listens, receives and prints data from the UART.
+
+## How to use example
+
+### Hardware Required
+
+The example can be run on any commonly available ESP32 development board. You will need a USB cable to connect the
+development board to a computer, and a simple one-wire cable for shorting two pins of the board.
+
+### Setup the Hardware
+
+The `RXD_PIN` and `TXD_PIN` which are configurable in the code (by default `GPIO4` and `GPIO5`) need to be shorted in
+order to receive back the same data which were sent out.
+
+### Configure the project
+
+```
+make menuconfig
+```
+or
+```
+idf.py menuconfig
+```
+
+* Set serial port under Serial Flasher Options.
+
+### Build and Flash
+
+Build the project and flash it to the board, then run monitor tool to view serial output:
+
+```
+make -j4 flash monitor
+```
+or
+```
+idf.py flash monitor
+```
+
+(To exit the serial monitor, type ``Ctrl-]``.)
+
+See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
+
+## Example Output
+
+You will receive the following repeating output from the monitoring console:
+```
+...
+I (3261) TX_TASK: Wrote 11 bytes
+I (4261) RX_TASK: Read 11 bytes: 'Hello world'
+I (4261) RX_TASK: 0x3ffb821c   48 65 6c 6c 6f 20 77 6f  72 6c 64                 |Hello world|
+...
+```
+
+## Troubleshooting
+
+If you do not see any output from `RX_TASK` then check if you have the `RXD_PIN` and `TXD_PIN` pins shorted on the board.

examples/peripherals/uart/uart_async_rxtxtasks/main/CMakeLists.txt

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+set(COMPONENT_SRCS "uart_async_rxtxtasks_main.c")
+set(COMPONENT_ADD_INCLUDEDIRS ".")
+
+register_component()

examples/peripherals/uart/uart_async_rxtxtasks/main/component.mk

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+#
+# Main Makefile. This is basically the same as a component makefile.
+#

examples/peripherals/uart/uart_async_rxtxtasks/main/uart_async_rxtxtasks_main.c

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+/* UART asynchronous example, that uses separate RX and TX tasks
+
+   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 "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "esp_system.h"
+#include "esp_log.h"
+#include "driver/uart.h"
+#include "soc/uart_struct.h"
+#include "string.h"
+
+static const int RX_BUF_SIZE = 1024;
+
+#define TXD_PIN (GPIO_NUM_4)
+#define RXD_PIN (GPIO_NUM_5)
+
+void init() {
+    const uart_config_t uart_config = {
+        .baud_rate = 115200,
+        .data_bits = UART_DATA_8_BITS,
+        .parity = UART_PARITY_DISABLE,
+        .stop_bits = UART_STOP_BITS_1,
+        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
+    };
+    uart_param_config(UART_NUM_1, &uart_config);
+    uart_set_pin(UART_NUM_1, TXD_PIN, RXD_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
+    // We won't use a buffer for sending data.
+    uart_driver_install(UART_NUM_1, RX_BUF_SIZE * 2, 0, 0, NULL, 0);
+}
+
+int sendData(const char* logName, const char* data)
+{
+    const int len = strlen(data);
+    const int txBytes = uart_write_bytes(UART_NUM_1, data, len);
+    ESP_LOGI(logName, "Wrote %d bytes", txBytes);
+    return txBytes;
+}
+
+static void tx_task()
+{
+    static const char *TX_TASK_TAG = "TX_TASK";
+    esp_log_level_set(TX_TASK_TAG, ESP_LOG_INFO);
+    while (1) {
+        sendData(TX_TASK_TAG, "Hello world");
+        vTaskDelay(2000 / portTICK_PERIOD_MS);
+    }
+}
+
+static void rx_task()
+{
+    static const char *RX_TASK_TAG = "RX_TASK";
+    esp_log_level_set(RX_TASK_TAG, ESP_LOG_INFO);
+    uint8_t* data = (uint8_t*) malloc(RX_BUF_SIZE+1);
+    while (1) {
+        const int rxBytes = uart_read_bytes(UART_NUM_1, data, RX_BUF_SIZE, 1000 / portTICK_RATE_MS);
+        if (rxBytes > 0) {
+            data[rxBytes] = 0;
+            ESP_LOGI(RX_TASK_TAG, "Read %d bytes: '%s'", rxBytes, data);
+            ESP_LOG_BUFFER_HEXDUMP(RX_TASK_TAG, data, rxBytes, ESP_LOG_INFO);
+        }
+    }
+    free(data);
+}
+
+void app_main()
+{
+    init();
+    xTaskCreate(rx_task, "uart_rx_task", 1024*2, NULL, configMAX_PRIORITIES, NULL);
+    xTaskCreate(tx_task, "uart_tx_task", 1024*2, NULL, configMAX_PRIORITIES-1, NULL);
+}