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69 lines
2.4 KiB
Markdown
69 lines
2.4 KiB
Markdown
# UART Select Example
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(See the README.md file in the upper level 'examples' directory for more information about examples.)
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The UART select example is for demonstrating the use of `select()` for
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synchronous I/O multiplexing on the UART interface. The example waits for a
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character from UART using `select()` until a blocking read without delay or a
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successful non-blocking read is possible.
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Please note that the same result can be achieved by using `uart_read_bytes()`
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but the use of `select()` allows to use it together with other virtual
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file system (VFS) drivers, e.g. LWIP sockets.
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This example can be used to develop applications for non-blocking read and write from/to various sources (UART,
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sockets, ...) where a ready resource can be served without being blocked by a busy resource.
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For a more comprehensive example please refer to `system/select`.
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## How to use example
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### Hardware Required
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The example can be run on any ESP32 development board connected to a PC with a single USB cable for communication
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through UART.
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### Configure the project
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```
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idf.py menuconfig
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```
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### Build and Flash
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Build the project and flash it to the board, then run monitor tool to view serial output:
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```
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idf.py -p PORT flash monitor
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```
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(To exit the serial monitor, type ``Ctrl-]``.)
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See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
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## Example Output
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You can see a similar output after flashing and monitoring the application:
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```
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...
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I (276) cpu_start: Pro cpu start user code
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I (294) cpu_start: Starting scheduler on PRO CPU.
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I (0) cpu_start: Starting scheduler on APP CPU.
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I (10295) uart_select_example: Timeout has been reached and nothing has been received
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I (15295) uart_select_example: Timeout has been reached and nothing has been received
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I (20295) uart_select_example: Timeout has been reached and nothing has been received
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```
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You can push any key on your keyboard to see the result of a successful detection by `select()` and subsequent
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blocking read (without delay). The following output shows the result of pushing `a` on the keyboard:
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```
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...
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I (15295) uart_select_example: Timeout has been reached and nothing has been received
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I (20295) uart_select_example: Timeout has been reached and nothing has been received
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I (20945) uart_select_example: Received: a
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I (25955) uart_select_example: Timeout has been reached and nothing has been received
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...
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```
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