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diff --git a/Smol Watch Project/My Project/hal/documentation/timer.rst b/Smol Watch Project/My Project/hal/documentation/timer.rst new file mode 100644 index 00000000..c5ca63d1 --- /dev/null +++ b/Smol Watch Project/My Project/hal/documentation/timer.rst @@ -0,0 +1,52 @@ +============================ +The Timer driver (bare-bone) +============================ + +The Timer driver provides means for delayed and periodical function invocation. + +A timer task is a piece of code (function) executed at a specific time or periodically by the timer after the task has +been added to the timers task queue. The execution delay or period is set in ticks, where one tick is defined as a +configurable number of clock cycles in the hardware timer. Changing the number of clock cycles in a tick automatically +changes execution delays and periods for all tasks in the timers task queue. + +A task has two operation modes, single-shot or repeating mode. In single-shot mode the task is removed from the task queue +and then is executed once, in repeating mode the task reschedules itself automatically after it has executed based on +the period set in the task configuration. +In single-shot mode a task is removed from the task queue before its callback is invoked. It allows an application to +reuse the memory of expired task in the callback. + +Each instance of the Timer driver supports infinite amount of timer tasks, only limited by the amount of RAM available. + +Features +-------- +* Initialization and de-initialization +* Starting and stopping +* Timer tasks - periodical invocation of functions +* Changing and obtaining of the period of a timer + +Applications +------------ +* Delayed and periodical function execution for middle-ware stacks and applications. + +Dependencies +------------ +* Each instance of the driver requires separate hardware timer capable of generating periodic interrupt. + +Concurrency +----------- +The Timer driver is an interrupt driven driver.This means that the interrupt that triggers a task may occur during +the process of adding or removing a task via the driver's API. In such case the interrupt processing is postponed +until the task adding or removing is complete. + +The task queue is not protected from the access by interrupts not used by the driver. Due to this +it is not recommended to add or remove a task from such interrupts: in case if a higher priority interrupt supersedes +the driver's interrupt, adding or removing a task may cause unpredictable behavior of the driver. + +Limitations +----------- +* The driver is designed to work outside of an operating system environment, the task queue is therefore processed in interrupt context which may delay execution of other interrupts. +* If there are a lot of frequently called interrupts with the priority higher than the driver's one, it may cause delay for triggering of a task. + +Knows issues and workarounds +---------------------------- +Not applicable |