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53 lines
2.6 KiB
ReStructuredText
53 lines
2.6 KiB
ReStructuredText
5 years ago
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============================
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The Timer driver (bare-bone)
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============================
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The Timer driver provides means for delayed and periodical function invocation.
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A timer task is a piece of code (function) executed at a specific time or periodically by the timer after the task has
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been added to the timers task queue. The execution delay or period is set in ticks, where one tick is defined as a
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configurable number of clock cycles in the hardware timer. Changing the number of clock cycles in a tick automatically
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changes execution delays and periods for all tasks in the timers task queue.
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A task has two operation modes, single-shot or repeating mode. In single-shot mode the task is removed from the task queue
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and then is executed once, in repeating mode the task reschedules itself automatically after it has executed based on
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the period set in the task configuration.
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In single-shot mode a task is removed from the task queue before its callback is invoked. It allows an application to
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reuse the memory of expired task in the callback.
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Each instance of the Timer driver supports infinite amount of timer tasks, only limited by the amount of RAM available.
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Features
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--------
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* Initialization and de-initialization
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* Starting and stopping
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* Timer tasks - periodical invocation of functions
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* Changing and obtaining of the period of a timer
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Applications
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------------
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* Delayed and periodical function execution for middle-ware stacks and applications.
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Dependencies
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------------
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* Each instance of the driver requires separate hardware timer capable of generating periodic interrupt.
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Concurrency
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-----------
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The Timer driver is an interrupt driven driver.This means that the interrupt that triggers a task may occur during
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the process of adding or removing a task via the driver's API. In such case the interrupt processing is postponed
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until the task adding or removing is complete.
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The task queue is not protected from the access by interrupts not used by the driver. Due to this
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it is not recommended to add or remove a task from such interrupts: in case if a higher priority interrupt supersedes
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the driver's interrupt, adding or removing a task may cause unpredictable behavior of the driver.
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Limitations
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-----------
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* 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.
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* 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.
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Knows issues and workarounds
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----------------------------
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Not applicable
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