Function-Call Feedback Latch

Break feedback loop involving data signals between function-call blocks

Libraries:
Simulink / Ports & Subsystems

Description

Use the Function-Call Feedback Latch block to break a feedback loop of data signals between one or more function-call blocks. Specifically, break a feedback loop formed in one of the following ways.

When function-call blocks connect to branches of the same function-call signal
Place the Function-Call Feedback Latch block on the feedback signal between the branched blocks. As a result, the latch block delays the signal at the input of the destination function-call block, and the destination function-call block executes prior to the source function-call block of the latch block.
To run this model, see Function-Call Blocks Connected to Branches of the Same Function-Call Signal.
When the loop involves parent and child function-call blocks, where the child initiator is inside the parent
Place the Function-Call Feedback Latch block on the feedback signal between the child and the parent. This arrangement prevents the signal value, read by the parent (FCSS1), from changing during execution of the child. In other words, the parent reads the value from the previous execution of the child (FCSS2).
To run this model, see Function-Call Feedback Latch on Feedback Signal Between Child and Parent.

Using the latch block is equivalent to selecting the Latch input for function-call feedback signals check box on the Inport block in the destination function-call subsystem or model. However, an advantage of the latch block over using the dialog parameter is that one can design the destination function-call subsystem or model in a modular fashion and then use it either in or out of the context of loops.

The Function-Call Feedback Latch block is better suited than Unit Delay or Memory blocks in breaking function-call feedback loops for the following reasons:

The latch block delays the feedback signal for exactly one execution of the source function-call block. This behavior is different from the Unit Delay or Memory blocks for cases where the function-call subsystem blocks may execute multiple times in a given simulation step.
Unlike the Unit Delay or Memory blocks, the latch block may be used to break loops involving asynchronous function-call subsystems.
The latch block can result in better performance, in terms of memory optimization, for generated code.

Examples

Function-Call Blocks Connected to Branches of the Same Function-Call Signal

In this model, a Function-Call Feedback Latch block is on the feedback signal between the branched blocks.

Open Model