This example shows how to use the ESP Timer feature. For detailed information on the functions and procedures used in this example, see [ESP Timer API Reference](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/system/esp_timer.html).
> **Note**: By default, all links to [ESP-IDF Programming Guide](https://docs.espressif.com/projects/esp-idf/en/latest/index.html) refer to the documentation for the ESP32. After clicking such a link, please remember to select your Espressif chip in the dropdown menu in the top-left corner.
The ESP Timer facilitates creation and handling of timers that invoke callback functions (dispatch callbacks) on timeout. ESP Timer is mainly used to perform delayed or periodic actions, such as delayed device start/stop or periodic sampling of sensor data.
ESP Timer hides the complexity associated with managing multiple timers, dispatching callbacks, accounting for clock frequency changes (if dynamic frequency scaling is enabled), and maintaining correct time after light sleep.
The subsections below give only absolutely necessary information. For full steps to configure ESP-IDF and use it to build and run projects, see [ESP-IDF Getting Started](https://docs.espressif.com/projects/esp-idf/en/latest/get-started/index.html#get-started).
### Required Hardware
* An Espressif development board
* USB A/micro USB B cable for power supply and serial communication
* Computer running Windows, Linux, or macOS
### Set Chip Target
In your example project directory, [set the chip target](https://docs.espressif.com/projects/esp-idf/en/latest/api-guides/tools/idf-py.html#select-the-target-chip-set-target):
This project has some Kconfig options set as default for this particular example in [sdkconfig.defaults](./sdkconfig.defaults). For more information about those and other Kconfig options, see [Project Configuration](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/kconfig.html).
To conveniently check or modify Kconfig options for this example, run:
Timers are used to execute a callback function as a delayed action. So the callback functions `periodic_timer_callback()` and `oneshot_timer_callback()` are the most important parts of this application example. They are defined for the periodic and one-shot timers respectively.
The struct `esp_timer_create_args_t` is used to initialize a timer. Its parameters are described in *ESP Timer API Reference* > [esp_timer_create_args_t](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/system/esp_timer.html#esp_timer_create_args_t).
To run a timer, it needs to be created first using the function `esp_timer_create()` and then started using either `esp_timer_start_periodic()` or `esp_timer_start_once()` depending on the timer type.
The function `esp_timer_dump()` is used to print the timer dumps which can be useful for debugging purposes. For details, see *ESP Timer API Reference* > [Debugging Timers](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/system/esp_timer.html#debugging-timers).
To make the output of the dump function more detailed, this example's file `sdkconfig.defaults` has the option `CONFIG_ESP_TIMER_PROFILING` set (see [Review Kconfig Options](#review-kconfig-options)).
To demonstrate that timekeeping continues correctly after light sleep, the example briefly enters light sleep using `esp_sleep_enable_timer_wakeup()` and `esp_light_sleep_start()`.
During light sleep, the CPU is not running, so callbacks cannot be dispatched. On wakeup, the system attempts to execute all unhandled callbacks if any, then ESP Timer resumes its normal operation.
### Stopping and Deleting Timers
Once the timers are not needed anymore, they are stopped and deleted to free up memory using `esp_timer_stop()` and `esp_timer_delete()`.
## Troubleshooting
For any technical queries, please open an [issue](https://github.com/espressif/esp-idf/issues) on GitHub. We will get back to you as soon as possible.
