esp-microsleep

A replacement for FreeRTOS vTaskDelay with subtick granularity.

Why?

Due to the way FreeRTOS works, it is impossible to achieve fine-grained delays in the millisecond or sub-millisecond region. Busy waiting is no alternative, since you will a) burn cycles and b) might trigger the FreeRTOS task watchdog.

How?

This little ESP-IDF component fixes this by leveraging the esp_timer subsystem. The currently running task starts a timer and waits for a notification from the timer's ISR.

Installation

1. Adjust your idf_component.yml file to depend on this component:

dependencies:
    mickeyl/esp_microsleep:
        git: "https://github.com/mickeyl/esp-microsleep.git"

2. Configure your project to allow for esp_timer dispatching via ISR:

   CONFIG_ESP_TIMER_SUPPORTS_ISR_DISPATCH_METHOD=y

3. Configure the proper amount of thread local storage. If you're not using thread local storage elsewhere in your app, 2 will be enough:

   CONFIG_FREERTOS_THREAD_LOCAL_STORAGE_POINTERS=2

4. Configure the appropriate thread local storage index:

   CONFIG_ESP_MICROSLEEP_TLS_INDEX=1

Usage

// Include the header file.
#include <esp_microsleep.h>

// Calibrate the compensation value (for more accurate sleep times).
esp_microsleep_calibrate();

// Call to delay the currently running task for 400 µs.
esp_microsleep_delay(400);

Implementation Notes

While the task is "waiting" for the notification to arrive, it is suspended via xTaskNotifyWait.

Since it takes a while from the timer alarm to get the task notification processed, you may achieve slightly longer sleep times than requested.

To compensate for that, you should call esp_microsleep_calibrate() which computes a value suitable for your system.

License

MIT.

Maintainer

This component is maintained by Dr. Michael 'Mickey' Lauer mlauer@vanille-media.de