1# UART Select Example 2 3(See the README.md file in the upper level 'examples' directory for more information about examples.) 4 5The UART select example is for demonstrating the use of `select()` for 6synchronous I/O multiplexing on the UART interface. The example waits for a 7character from UART using `select()` until a blocking read without delay or a 8successful non-blocking read is possible. 9 10Please note that the same result can be achieved by using `uart_read_bytes()` 11but the use of `select()` allows to use it together with other virtual 12file system (VFS) drivers, e.g. LWIP sockets. 13 14This example can be used to develop applications for non-blocking read and write from/to various sources (UART, 15sockets, ...) where a ready resource can be served without being blocked by a busy resource. 16 17For a more comprehensive example please refer to `system/select`. 18 19## How to use example 20 21### Hardware Required 22 23The example can be run on any ESP32, ESP32-S and ESP32-C series based development board connected to a computer with a single USB cable for communication 24through UART. 25 26### Configure the project 27 28``` 29idf.py menuconfig 30``` 31 32### Build and Flash 33 34Build the project and flash it to the board, then run monitor tool to view serial output: 35 36``` 37idf.py -p PORT flash monitor 38``` 39 40(To exit the serial monitor, type ``Ctrl-]``.) 41 42See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects. 43 44## Example Output 45 46You can see a similar output after flashing and monitoring the application: 47 48``` 49... 50I (276) cpu_start: Pro cpu start user code 51I (294) cpu_start: Starting scheduler on PRO CPU. 52I (0) cpu_start: Starting scheduler on APP CPU. 53I (10295) uart_select_example: Timeout has been reached and nothing has been received 54I (15295) uart_select_example: Timeout has been reached and nothing has been received 55I (20295) uart_select_example: Timeout has been reached and nothing has been received 56``` 57 58You can push any key on your keyboard to see the result of a successful detection by `select()` and subsequent 59blocking read (without delay). The following output shows the result of pushing `a` on the keyboard: 60 61``` 62... 63I (15295) uart_select_example: Timeout has been reached and nothing has been received 64I (20295) uart_select_example: Timeout has been reached and nothing has been received 65I (20945) uart_select_example: Received: a 66I (25955) uart_select_example: Timeout has been reached and nothing has been received 67... 68``` 69
