Added an asynchronous UART example, using separate RX and TX tasks.

Signed-off-by: krzychb <krzychb@gazeta.pl>

examples/peripherals/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_async_rxtxtasks/README.md

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+UART asynchronous example, that uses separate RX and TX tasks
+=============================================================
+
+Starts two FreeRTOS tasks:
+  - One task for transmitting 'Hello world' via the UART.
+  - One task for receiving from the UART.
+
+If you'd like to see your ESP32 receive something, simply short
+TXD_PIN and RXD_PIN. By doing this data transmitted on TXD_PIN will
+be received on RXD_PIN. See the definitions of TXD_PIN and RXD_PIN
+in ./main/uart_async_rxtxtasks_main.c.

examples/peripherals/uart_async_rxtxtasks/main/component.mk

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

examples/peripherals/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);
+        }
+    }
+    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);
+}