MATLAB REAL-TIME WORKSHOP 7 - TARGET LANGUAGE COMPILER Podręcznik Użytkownika Pobierz pdf (Strona 216)

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7 Models with Multiple Sample Rates

7-16

This timing diagram illustrates two problems:

1 Execution of the slower block is split over more than one faster block

interval. In this case the faster task executes a second time before the slower

task has completed execution. This means the inputs to the slower task can

change, causing unpredictable results.

2 The faster block executes before the slower block (which is backwards from

the way Simulink operates). In this case, the 1 sec block executes first; but

the inputs to the faster task have not been computed. This can cause

unpredictable results.

To eliminate these problems, you must insert a Unit Delay block between the

slower and faster blocks. The sample rate for a Unit Delay block must be set to

that of the block that is driving it (i.e., the slower block):

This pictures shows the timing sequence that results with the added Unit

Delay block:

Slower

Faster

Block

T=2sec

T=1sec

Unit Delay

Block

T=2sec

1 2 ... 211 212 213 214 215 216 217 218 219 220 221 ... 385 386

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MATLAB REAL-TIME WORKSHOP 7 - TARGET LANGUAGE COMPILER Podręcznik Użytkownika Strona 216

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