MATLAB SIMULINK 7 - DEVELOPING S-FUNCTIONS Guide de l'utilisateur télécharger pdf (Page 19)

Introduction

1-13

• A discrete S-function that changes at a specified ra te should register the

discrete sample time pair,

[discrete_sample_time_period, offset],

where

discrete_sample_period > 0.0

and

0.0 ≤ offset < discrete_sample_period

• A discrete S-function that changes a t a variable rate should register the

variable step discrete sample time:

[VARIABLE_SAMPLE_TIME, 0.0]

The mdlGetTimeOfNextVarHit routine is called to get the tim e of the next

sample hit for the variable step discrete task.

If your S-function has no intrinsic sample t ime, then you must indicate that

your sample time is inherited. There are two cases:

• An S-function that changes as its input changes, even during minor

integration steps, should register the

[INHERITED_SAMPLE_TIME, 0.0]

sample time.

• An S-function that changes as its input changes, but doesn’t change during

minor integration steps (that is, remains fixed during minor time steps),

should register the

[INHERITED_SAMPLE_TIME, FIXED_IN_MINOR_STEP_OFFSET] sample time.

For example, most discrete-time S-functions must register this sample time

when inheriting the input sample time.

Sample S-Functions

ItmaybehelpfultoexaminesomesampleS-functionsasyoureadthenext

chapters. Examples are storedin these subdirectories under the MATLAB root

directory:

• M-files:

toolbox/simulink/blocks

• CMEX-files:simulink/src

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MATLAB SIMULINK 7 - DEVELOPING S-FUNCTIONS Guide de l'utilisateur Page 19