Handling Timer Queuing Conflicts - MATLAB & Simulink (original) (raw)

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During busy times, in multiple-execution scenarios, the timer might need to add the timer callback function (TimerFcn) to the MATLAB® execution queue before the previously queued execution of the callback function has been completed. The BusyMode property affects behavior only when the ExecutionMode property is set toFixedRate. For other values of ExecutionMode, there cannot be overlapping attempts to execute the timer callback function because the delay between executions is always relative to the completion of the previous execution.

You can determine how the timer object handles this scenario by setting theBusyMode property to use one of these modes:

Drop Mode (Default)

If you specify 'drop' as the value of theBusyMode property, the timer object adds the timer callback function to the execution queue only when the queue is empty. If the execution queue is not empty, the timer object skips the execution of the callback.

For example, suppose you create a timer with a period of 1 second, but a callback that requires at least 1.6 seconds, as shown here formytimer.m.

function mytimer() t = timer;

t.Period         = 1;
t.ExecutionMode  = 'fixedRate';
t.TimerFcn       = @mytimer_cb;
t.BusyMode       = 'drop';
t.TasksToExecute = 5;
t.UserData       = tic;

start(t)

end

function mytimer_cb(h,~) timeStart = toc(h.UserData) pause(1.6); timeEnd = toc(h.UserData) end

This table describes how the timer manages the execution queue.

Error Mode

The 'error' mode for the BusyMode property is similar to the 'drop' mode: In both modes, the timer allows only one instance of the callback in the execution queue. In'error' mode, when the queue is nonempty, the timer calls the function that you specify by using the ErrorFcn property, and then stops processing. The currently running callback function completes, but the callback in the queue does not execute.

For example, modify mytimer.m (described in the previous section) so that it includes an error handling function and setsBusyMode to 'error'.

function mytimer() t = timer;

t.Period         = 1;
t.ExecutionMode  = 'fixedRate';
t.TimerFcn       = @mytimer_cb;
t.ErrorFcn       = @myerror;
t.BusyMode       = 'error';
t.TasksToExecute = 5;
t.UserData       = tic;

start(t)

end

function mytimer_cb(h,~) timeStart = toc(h.UserData) pause(1.6); timeEnd = toc(h.UserData) end

function myerror(h,~) disp('Reached the error function') end

This table describes how the timer manages the execution queue.

Queue Mode

If you specify 'queue', the timer object waits until the currently executing callback function finishes before queuing the next execution of the timer callback function.

In 'queue' mode, the timer object tries to make the average time between executions equal the amount of time specified in thePeriod property. If the timer object has to wait longer than the time specified in the Period property between executions of the timer function callback, it shortens the time period for subsequent executions to make up the time.

For example, modify mytimer.m (described in the previous section) so that BusyMode is set to'queue'.

function mytimer() t = timer;

t.Period         = 1;
t.ExecutionMode  = 'fixedRate';
t.TimerFcn       = @mytimer_cb;
t.ErrorFcn       = @myerror;
t.BusyMode       = 'queue';
t.TasksToExecute = 5;
t.UserData       = tic;

start(t)

end

function mytimer_cb(h,~) timeStart = toc(h.UserData) pause(1.6); timeEnd = toc(h.UserData) end

function myerror(h,~) disp('Reached the error function') end

This table describes how the timer manages the execution queue.

See Also

timer

Related Topics

• Timer Callback Functions