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time-tick-scheduler

Versione italiana

Task scheduler based on time ticks

This scheduler allows the dynamic creation and deletion at runtime of tasks, as well as the enabling and disabling of the same, always at runtime.

Choose the various times in play in an appropriate manner, such as to allow easy automatic calculation of both the base time (so that it is not too small) and the sentinel counters of the time ticks of the events (multiples of the base time).

Events can be inserted, associated with their times, without following a particular order of invocations using one of the two functions addPeriodicEvent() and addAsyncEvent().

To bear in mind that:

  • For each time defined in the scheduler it is possible to enter up to 127 events, a limit imposed by the bit depth chosen for some counting variables.
  • #define NEVENTS in the Scheduler2.h file defines the current maximum number, for default set to 20
  • #define NTIMES in the Scheduler2.h file defines the current maximum number, for default set to 20

The time base of the time ticks() is automatically chosen by calculating the greatest common divisor of the various times involved.

If several tasks with different periodicity occur at the same time (tick), priority is given to the slower ones so that if any delay of a fast task were to spread across several fast ticks, the introduced time error would affect only the following first short tick and would have no effect on slow ticks (of greater periodicity) since they are always served first.

The library allows an alternative to resampling in the loop() to compensate for delays of a task, exploiting the forced prerelease property of a task that has interrupts. If the ticks are interrupt based then they always occur in the exact time assigned to them even in the presence of a task that delays its execution.

Examples:

Methods of class Scheduler():

  • Scheduler() Costruttore
  • bool addPeriodicEvent(PEventCallback pevnt, uint8_t priority, unsigned long every, bool enabled = true). Adds a periodic event defined by:
    • pevnt: callback event to be scheduled
    • priority execution order or id of the task in a certain time slot
    • every: time slot in which the event should be repeated. The function defines a new slot if there is no one with the same time, or simply associates the event to an existing slot. Together with the priority field, identifies the periodic event.
    • enabled: if is true (default value) the event is registered and activated, if is false the event is both registered and activated.
  • bool addAsyncEvent(PEventCallback pevnt, uint8_t priority, unsigned long when, unsigned long howlong, unsigned long every, bool repeat). Adds an aperiodic event additionally defined by:
  • when: time slot where the event starts. The function does not define a new slot, it manages a timer updated in poling with the periodicity of the slot every.
  • howlong: how long the scheduling lasts. No new slot is defined for this time but only for the every time.
  • every: base time slot in which the event must be repeated (base periodicity). The function defines a new slot if one with the same time does not exist, or simply associates the event to an existing slot. Together with the priority field, identifies the aperiodic event. To cancel, the event can be identified with the pair (priority, every).
  • bool Scheduler::deletePeriodicEvent(uint8_t priority, unsigned long every, bool test = false). Deletes a periodic event identified by its priority and its every base periodicity. Clears both periodic and asynchronous events. The optional test parameter performs the "dry" operation for test reasons, i.e. verifying its feasibility without performing any deletion (it only returns the boolean parameter of successful deletion. By default, the test function is disabled.
  • void scheduleAll(). Perform all tasks. To be inserted in the loop() or in a callback both called at regular intervals.
  • unsigned getTimebase(). Returns the base time of time ticks.
  • long getTime(unsigned long when).Returns the time tick count of the time supplied as a parameter.
  • bool getEventState(uint8_t priority, unsigned long every). Returns the status (enabled or disabled) of an event. An event is identified by the pair (time every in milliseconds, priority).
  • bool setEventState(uint8_t priority, bool state, unsigned long every). Set the status (enabled or disabled) of an event.
  • bool enableEvent(uint8_t priority, unsigned long every). Enable an event identified by the pair (time every in milliseconds, priority).
  • bool disableEvent(uint8_t priority, unsigned long every). Disable an event identified by the pair (time every in milliseconds, priority).
  • bool toggleEvent(uint8_t priority, unsigned long every). Change the state of an event identified by the pair (time every in milliseconds, priority).
  • void scheduleAllISRFlagged(bool noflag=false). Execute all tasks upon signaling a flag asserted by void timerISR() . To be placed in the loop() where the flag is polled every loop. A call executes the tasks associated with a tick only if the flag is asserted, otherwise it does nothing.
    • noflag: disable flag check of running task. Defaults to false. Set it to false if void scheduleAllISRFlagged(true) can be executed directly inside an isochronous time-base callback. Several consecutive calls each make a tick by invoking all the tasks associated with it.
  • void timerISR(void). ISR called at regular intervals by a HW timer (interrupt).

Sitography:

Versione italiana