Difference between revisions of "Timers"
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| − | Timers | + | == Timers == |
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| + | Timers can be used to control periodic tasks as well as implement sophisticated algorithms. The implementation of each type of timer is platform-dependent and has different properties that make them useful in specific situations; some timers have low granularity (seconds) and overflow once in tens of years, and others provide high granularity (microseconds), but overflow rapidly. There are 5 types of timers provided by Contiki: | ||
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| + | * timer | ||
| + | * stimer | ||
| + | * ctimer | ||
| + | * etimer | ||
| + | * rtimer | ||
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| + | The functions of all types of timers are located in the folder '''core/sys/{timer, stimer, ctimer, etimer, rtimer}.{c,h}'''. A complete documentation of Timers in Contiki can be found [https://github.com/contiki-os/contiki/wiki/Timers here]. | ||
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| + | The '''timer''' and '''stimer''' provide the simplest form of timers and are used to check if a time period has passed. The applications need to ask the timers if they have expired. The difference between these is the resolution of time: timers use system clock ticks while stimers use seconds to allow much longer time periods. Unlike the other timers, the timer and stimer libraries can be safely used from interrupts which makes them especially useful in low level drivers. | ||
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| + | The '''etimer''' library provides event timers and are used to schedule events to Contiki processes after a period of time. They are used in Contiki processes to wait for a time period while the rest of the system can work or enter low power mode. | ||
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| + | The '''ctimer''' library provides callback timers and are used to schedule calls to callback functions after a period of time. Like event timers, they are used to wait for some time while the rest of the system can work or enter low power mode. Since the callback timers call a function when a timer expires, they are especially useful in any code that do not have an explicit Contiki process such as protocol implementations. | ||
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| + | The '''rtimer''' library provides scheduling of real-time tasks. The rtimer library preempts any running Contiki process in order to let the real-time tasks execute at the scheduled time. The real-time tasks are used in time critical codes. | ||
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Revision as of 15:50, 5 February 2014
Contents
Timers
Timers can be used to control periodic tasks as well as implement sophisticated algorithms. The implementation of each type of timer is platform-dependent and has different properties that make them useful in specific situations; some timers have low granularity (seconds) and overflow once in tens of years, and others provide high granularity (microseconds), but overflow rapidly. There are 5 types of timers provided by Contiki:
- timer
- stimer
- ctimer
- etimer
- rtimer
The functions of all types of timers are located in the folder core/sys/{timer, stimer, ctimer, etimer, rtimer}.{c,h}. A complete documentation of Timers in Contiki can be found here.
The timer and stimer provide the simplest form of timers and are used to check if a time period has passed. The applications need to ask the timers if they have expired. The difference between these is the resolution of time: timers use system clock ticks while stimers use seconds to allow much longer time periods. Unlike the other timers, the timer and stimer libraries can be safely used from interrupts which makes them especially useful in low level drivers.
The etimer library provides event timers and are used to schedule events to Contiki processes after a period of time. They are used in Contiki processes to wait for a time period while the rest of the system can work or enter low power mode.
The ctimer library provides callback timers and are used to schedule calls to callback functions after a period of time. Like event timers, they are used to wait for some time while the rest of the system can work or enter low power mode. Since the callback timers call a function when a timer expires, they are especially useful in any code that do not have an explicit Contiki process such as protocol implementations.
The rtimer library provides scheduling of real-time tasks. The rtimer library preempts any running Contiki process in order to let the real-time tasks execute at the scheduled time. The real-time tasks are used in time critical codes.
