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esp-idf/examples/system/eventfd/README.md

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Supported Targets ESP32 ESP32-C2 ESP32-C3 ESP32-C5 ESP32-C6 ESP32-H2 ESP32-P4 ESP32-S2 ESP32-S3

eventfd example

The example demonstrates the use of eventfd() to collect events from other tasks and ISRs in a select() based main loop. The example starts two tasks and installs a timer interrupt handler:

  1. The first task writes to the first eventfd periodically.
  2. The timer interrupt handler writes to the second eventfd.
  3. The second task collects the event from two fds with a select() loop.

How to use example

Hardware Required

This example should be able to run on any commonly available ESP32, ESP32S2, ESP32S3 or ESP32C3 development board.

Configure the project

idf.py menuconfig

The default config will work.

Build and Flash

Build the project and flash it to the board, then run monitor tool to view serial output:

idf.py -p PORT flash monitor

(Replace PORT with the name of the serial port to use.)

(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

The following log output should appear when the example runs (note that the bootloader log has been omitted).

I (4340) eventfd_example: Elapsed since test start: 2003 ms
I (4340) eventfd_example: Select timeout
I (4830) eventfd_example: Elapsed since test start: 2499 ms
I (4830) eventfd_example: TimerEvent fd event triggered
I (5830) eventfd_example: Elapsed since test start: 3493 ms
I (5830) eventfd_example: Progress fd event triggered
I (7330) eventfd_example: Elapsed since test start: 4999 ms
I (7330) eventfd_example: TimerEvent fd event triggered
I (7330) eventfd_example: =================================
I (7340) eventfd_example: Select timeouted for 1 times
I (7340) eventfd_example: Timer triggered for 2 times
I (7350) eventfd_example: Progress triggered for 1 times
I (7360) eventfd_example: =================================
I (9330) eventfd_example: Elapsed since test start: 6993 ms
I (9330) eventfd_example: Progress fd event triggered
I (9830) eventfd_example: Elapsed since test start: 7499 ms
I (9830) eventfd_example: TimerEvent fd event triggered
I (11840) eventfd_example: Elapsed since test start: 9503 ms
I (11840) eventfd_example: Select timeout
I (12330) eventfd_example: Elapsed since test start: 9999 ms
I (12330) eventfd_example: TimerEvent fd event triggered
I (12330) eventfd_example: =================================
I (12340) eventfd_example: Select timeouted for 2 times
I (12340) eventfd_example: Timer triggered for 4 times
I (12350) eventfd_example: Progress triggered for 2 times
I (12360) eventfd_example: =================================

Diagram

The following diagram shows, with a timeline, the order of the events:

Timeline