Upon waking up, the system gets the differenceīetween the counters and calls a function that advances the esp_timer counter. Instead, the time is counted by the RTC counter. esp_timer during light sleep ĭuring light sleep, the esp_timer counter stops and no callback functions are called.
The context switch will be done after all ISR dispatch timers have been processed, if required by the system. Timer callbacks which are processed by ESP_TIMER_ISR method should not call the context switch call - portYIELD_FROM_ISR(), instead of this you should use the esp_timer_isr_dispatch_need_yield() function. Keep the callback functions as short as possible otherwise it will affect all timers. To restart a running timer, call esp_timer_stop() first, then call one of the start functions. Note that the timer must not be running when esp_timer_start_once() or esp_timer_start_periodic() is called. The timer keeps running until esp_timer_stop() is called. To start the timer in periodic mode, call esp_timer_start_periodic(), passing the period with which the callback should be called.
When the callback gets called, the timer is considered to be stopped. To start the timer in one-shot mode, call esp_timer_start_once(), passing the time interval after which the callback should be called. The timer can be started in one-shot mode or in periodic mode. To delete the timer when it is no longer needed, call esp_timer_delete(). To create a timer, call esp_timer_create(). This callback function is called from the esp_timer task each time the timer elapses. Timer has a callback function associated with it. Single timer is represented by esp_timer_handle_t type. Consider using dedicated hardware peripherals or DMA features if you find that a timer with small period is required.
#Itimter virtual itimer real software#
Periodic software timers with period of less than 50us are not practical since they would consume most of the CPU time. Periodic esp_timer also imposes a 50us restriction on the minimal timer period. If esp_timer_start_once() is called with a timeout value less than 20us, the callback will be dispatched only after approximately 20us. Therefore, there is a lower limit to the timeout value of one-shot esp_timer. This method is useful for some simple callbacks which aim for lower latency.Ĭreating and starting a timer, and dispatching the callback takes some time. Timer callbacks are dispatched directly from the timer interrupt handler. For example, this will happen if an SPI Flash operation is in progress.ĮSP_TIMER_ISR. If other tasks with priority higher than esp_timer are running, callback dispatching will be delayed until esp_timer task has a chance to run. Because all the callbacks are dispatched from the same task, it is recommended to only do the minimal possible amount of work from the callback itself, posting an event to a lower priority task using a queue instead. Timer callbacks are dispatched from a high-priority esp_timer task. Available only if CONFIG_ESP_TIMER_SUPPORTS_ISR_DISPATCH_METHOD is enabled (by default disabled).ĮSP_TIMER_TASK. Timer callbacks can be dispatched by two methods:ĮSP_TIMER_ISR.
Internally, esp_timer uses a 64-bit hardware timer, where the implementation depends on the target. Raising the level, the interrupt handler can reduce the timer processing delay.Įsp_timer set of APIs provides one-shot and periodic timers, microsecond time resolution, and 64-bit range. It allows to set this: 1, 2 or 3 level (by default 1).
This means that some facility needs to be built on top of the hardware timer to manage the list of pending events can dispatch the callbacks for these events as corresponding hardware interrupts happen.Īn interrupt level of the handler depends on the CONFIG_ESP_TIMER_INTERRUPT_LEVEL option. For example, application components may need timer events to fire at certain times in the future, but the hardware timer only contains one “compare” value used for interrupt generation.
#Itimter virtual itimer real free#
Hardware timers are free from both of the limitations, but often they are less convenient to use. Timer callbacks are dispatched from a low-priority task Maximum resolution is equal to RTOS tick period High Resolution Timer (ESP Timer) Overview Īlthough FreeRTOS provides software timers, these timers have a few limitations:
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