Different behaviour in model when inserting a scope in the design.

Hi,

We are a group that are implementing the physical layer of the IEEE 802.11a standard in a course at the university. However we have hit a problem that we can not solve. Our examiner has just told us to ignore it and move on but that is not something we are happy to do.

Our design is built around one transmitter and one receiver. The problem is in the receiver when trying to generate a valid signal when we have detected the data transmission. If we however adds a scope that observs both the valid signal in the transmitter and the receiver the valid signal is generated correctly. But without the scope it is not.

So the question is why does the insertion of a scope change the behaviour of the system? Shouldn't the scope just observe?

We are using simulink 7.3 (R2009a)

[Fangjun Jiang]

Are you generating C code from your Simulink model and then run it in a hardware target? I know there is bug reported regarding code generation involving the Scope block.

Answer 1

[Guy Rouleau]

Enable the block Sorted Order and see if it changes when adding the scope or not:

http://www.mathworks.com/help/toolbox/simulink/ug/f13-91940.html

Try disabling some optimization like Conditional input branch execution

http://www.mathworks.com/help/toolbox/simulink/gui/bq7cqu2-1.html#bq7cq0i-1

If these options change the results, it is because either you use the blocks in a way that they have not been designed for, or this is a bug.

I recommend contacting support with your model to get a clear explanation, without the model this is just guessing.

[Jonas]

Thanks for your answers. When looked into we found that the optimization does not affect the design but the order indeed changes inside the design once the scope is added/removed. However we have not been able to change the order of execution without affecting other parts of the design but at least now we know were to look so once more thank you Guy.