A function-call subsystem is a subsystem that another block can invoke directly during a simulation. It is analogous to a function in a procedural programming language. Invoking a function-call subsystem is equivalent to invoking the output methods (See Block Methods) of the blocks that the subsystem contains in sorted order (See How Simulink Determines the Sorted Order). The block that invokes a function-call subsystem is called the function-call initiator. Stateflow®, Function-Call Generator, and S-function blocks can all serve as function-call initiators.
To create a function-call subsystem, drag a Function-Call Subsystem block from the Ports & Subsystems library into your model and connect a function-call initiator to the function-call port displayed on top of the subsystem. You can also create a function-call subsystem from scratch. First create a Subsystem block in your model and then create a Trigger block in the subsystem. Next, on the Trigger block parameters pane, set the Trigger type to function-call.
You can configure a function-call subsystem to be triggered (the default) or periodic by setting the Sample time type of its Trigger port to be triggered or periodic, respectively. A function-call initiator can invoke a triggered function-call subsystem zero, one, or multiple times per time step. The sample times of all the blocks in a triggered function-call subsystem must be set to inherited (-1).
A function-call initiator can invoke a periodic function-call subsystem only once per time step and must invoke the subsystem periodically. If the initiator invokes a periodic function-call subsystem aperiodically, the simulation is halted and an error message is displayed. The blocks in a periodic function-call subsystem can specify a noninherited sample time or inherited (-1) sample time. All blocks that specify a noninherited sample time must specify the same sample time. For example, if one block specifies 0.1 as the sample time, all other blocks must specify a sample time of 0.1 or -1. If a function-call initiator invokes a periodic function-call subsystem at a rate that differs from the sample time specified by the blocks in the subsystem, the simulation halts and an error message appears.
Note: During range checking, the design minimum and maximum are back-propagated to the actual source port of the function-call subsystem, even when the function-call subsystem is not enabled.
To prevent this back propagation, add a Signal Conversion block and a Signal Specification block after the source port, set the Output of the Signal Conversion block to Signal copy, and specify the design minimum and maximum on the Signal Specification block instead of specifying them on the source port.
For more information, see Function-Call Subsystems and S-Functions.