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Idle Task

Create free-running task

  • Idle Task block


The Idle Task block and the subsystem connected to it specify functions in the downstream subsystem to execute as background tasks. The tasks executed through the Idle Task block are of the lowest priority, lower than that of the base rate task.

This block is not supported on target computers that run an operating system.

Vectorized Output



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Optional simulated interrupt for testing asynchronous interrupt behavior during Simulink® simulation.

Port Dependencies

To enable this port, select parameter Enable simulation input.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64


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Numbers that identify the background tasks and task preemption flags, represented as vectors. A task identifier vector stores numbers that identify the background tasks.

For each background task, the preemption flag vector stores a flag that indicates whether the task can be preempted. Unless the preemption flag vector contains one element, the number of elements in the preemption flag vector must match the length of the task identifier vector. If the preemption flag vector has the same number of elements as the task identifier vector, each task represented in the task identifier vector has the preemption setting defined by the value of the corresponding element in the preemption flag vector. When the preemption flag vector contains one element, the flag setting applies to the entire task identifier vector.

A higher-priority task cannot preempt a lower-priority task that cannot be preempted.

Data Types: uint8


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Specify task identifiers for functions that are in the downstream subsystem as a vector of integers in the range 0 to 15. The vector must contain the same number of values as the number of functions in the downstream subsystem. For example, the default vector [1 2] indicates that the downstream subsystem contains two functions.

The number of values that you enter corresponds to the number of functions in the downstream subsystem. The values that you specify determine the execution order of the functions. For example, the vector [2 3 1] indicates that:

  • The subsystem contains three functions.

  • The third function executes first.

  • The first function executes second.

  • The second function executes third.

After the functions execute, the Idle Task block cycles back and repeats the execution of the functions in the same order.

Specify preemption flags for the tasks specified by the Task numbers parameter as a vector of up to 16 ones and zeros. Higher-priority interrupts can preempt interrupts that have a lower priority. To control preemption, use the preemption flags to specify whether an interrupt can be preempted.

The value 1 indicates that the interrupt for the corresponding task can be preempted. The value 0 indicates that the interrupt cannot be preempted. You have the option of specifying:

  • One preemption value that applies to the entire vector that you specify for Task numbers.

  • A preemption value for each task identified in the vector that you specify for Task numbers. Specify the flag values in the order that corresponds to the order of the tasks in Task numbers.

For example, if you specify the vector [2 3 1] for Task numbers and [0] for Preemption flags, tasks 1, 2, and 3 cannot be preempted. If you specify [1 1 0] for Preemption flags, tasks 2 and 3 can be preempted and task 1 cannot be preempted.

Select this parameter to create an input port that receives interrupt input for model simulation. Use the port to connect and test asynchronous interrupt processing behavior for one or more simulated interrupt sources during Simulink model simulation.

Version History

Introduced in R2011a