MATLAB SIMULINK 7 - DEVELOPING S-FUNCTIONS Guida Utente Scaricare il pdf (Pagina 148)

3 Writing S-Functions As C-MEX files

3-104

ssSetInputPortReusable

(S,inputPortIdx,value)

Used in mdlInitializeSizes (after

ssSetNumInputPorts) to specify whether the input port

memory buffer can be reuse d by other signals in the

model. This macro can tak e on two values:

• Off (

value=0) — specifies that the input por t is not

reusable. This is the default.

• On (

value=1) — specifies that the input port is

reusable.

In Simulink, reusable sign als share the same memory

space. When this macro is turned on, t he input port

signal to the S-function may be reused by other signals in

the model. This reuse results in less memory use during

Simulink simulation and more efficiency in the

Real-Time Workshop generated code.

You must use caut ion when using this macro; y ou can

safely turn it on only if the S-function reads its input port

signal in its

mdlOutputs routine and does not access this

input port sig nal until the next call to

mdlOutputs.

When an S-functions’s input port signal is reused, other

signals in the model overwrite it prior to the execution of

mdlUpdate, mdlDerivatives, or other run-time

S-function routines. For example, if the S-function reads

the input port signal in its

mdlUpdate routine, or reads

the input port signal in the

mdlOutputs routine and

expectsthisvaluetobepersistentuntiltheexecutionof

its

mdlUpdate routine, turning this at tribute on is

incorrect and will lead to erroneous results.

The d efault setting, o ff, is safe. It prevents any reuse of

the S-function inp ut po r t signals, which means that the

inport port signals have the same value in any run-time

S-function routine during a single execution of the

simulation loop.

Table 3-7: Input and Output Port Signal SimStruct Macros (Continued)

Macro Description

1 2 ... 143 144 145 146 147 148 149 150 151 152 153 ... 209 210

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