7.9 KiB
| Supported Targets | ESP32 | ESP32-C2 | ESP32-C3 | ESP32-C6 | ESP32-H2 | ESP32-P4 | ESP32-S2 | ESP32-S3 |
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ESP Timer Example (High Resolution Timer)
(See the README.md file in the upper level 'examples' directory for more information about examples.)
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.
Note: By default, all links to ESP-IDF Programming Guide 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.
Overview
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.
Usage
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.
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:
idf.py set-target <target>
For example, to set esp32 as the chip target, run
idf.py set-target esp32
Review Kconfig Options
This project has some Kconfig options set as default for this particular example in sdkconfig.defaults. For more information about those and other Kconfig options, see Project Configuration.
To conveniently check or modify Kconfig options for this example, run:
idf.py menuconfig
Build and Flash
Build the project, flash it to your development board, then run the monitor tool to view serial output:
idf.py build flash monitor
If the above command fails, try specifying your board's serial port name explicitly:
# Replace PORT with your board's serial port name
idf.py -p PORT build flash monitor
Exit the Serial Monitor
To exit the serial monitor, use Ctrl + ].
Example Output
If you see the following output log, your example should be running correctly:
...
I (294) example: Started timers, time since boot: 9662 us
periodic 500000 509644 1 0 0 0
one-shot 0 5009654 1 0 0 0
I (794) example: Periodic timer called, time since boot: 509694 us
I (1294) example: Periodic timer called, time since boot: 1009671 us
I (1794) example: Periodic timer called, time since boot: 1509671 us
I (2294) example: Periodic timer called, time since boot: 2009671 us
periodic 500000 2509644 1 4 0 542
one-shot 0 5009654 1 0 0 0
I (2794) example: Periodic timer called, time since boot: 2509671 us
I (3294) example: Periodic timer called, time since boot: 3009671 us
I (3794) example: Periodic timer called, time since boot: 3509671 us
I (4294) example: Periodic timer called, time since boot: 4009671 us
periodic 500000 4509644 1 8 0 1026
one-shot 0 5009654 1 0 0 0
I (4794) example: Periodic timer called, time since boot: 4509671 us
I (5294) example: Periodic timer called, time since boot: 5009669 us
I (5294) example: One-shot timer called, time since boot: 5009788 us
I (5294) example: Restarted periodic timer with 1s period, time since boot: 5012675 us
I (6294) example: Periodic timer called, time since boot: 6012692 us
periodic 1000000 7012666 2 11 0 1391
one-shot 0 0 1 1 0 11472
I (7294) example: Periodic timer called, time since boot: 7012692 us
I (8294) example: Periodic timer called, time since boot: 8012692 us
periodic 1000000 9012666 2 13 0 1639
one-shot 0 0 1 1 0 11472
I (9294) example: Periodic timer called, time since boot: 9012692 us
I (10294) example: Periodic timer called, time since boot: 10012692 us
I (10314) example: Entering light sleep for 0.5s, time since boot: 10024351 us
I (10314) example: Woke up from light sleep, time since boot: 10525143 us
...
Example Breakdown
The subsections below walk you through the important parts of the application example.
Creating Callback Functions
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.
Setting Timer Configuration Parameters
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.
The defined struct instance is then used in the function esp_timer_create().
Creating and Starting Timers
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.
Printing Timer Dumps
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.
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).
Entering and Waking Up from Light Sleep
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 on GitHub. We will get back to you as soon as possible.