Zedboard Simulink External mode: Sample time - real time

Question

Hello!
I am using a ZedBoard with the System Generator, Matlab/Simulink. There I have a model using VDHL blocks for the FPGA and some other Simulink blocks for the ARM controller on the Zedboard. There is no problem to simulate the model using the external mode.
But when I am reducing the sampling time of the other Simulink blocks, for example a "Pulse Generator Block", the simulation using the external mode becomes slow. I mean that for example in 10 seconds the simulation just passes one second. For my hardware I need real time behavior.
I am able to simulate with a sample time to 1e-4; when I reduce it to 1e-5 the problem starts.
I have no idea, where the bottleneck is. Is the controller on the Zedboard to slow, or is there a problem with the external mode? Is there a possibility to get some information about the load of the controller?

I hope that I was able to bring my problem to the point.
Best regards
Georg

mbrown · Accepted Answer

This is really a question for the MathWorks support forum. The behavior your seeing has to do with how MATLAB simulates. What you describe typically occurs when there are disparate sample times in a system, forcing the solver to calculate millions of intermediate results for a single sample in the slower domain of the model.

Motor Control is an excellent example of this behavior, where the ADC run in the MSPS range, while the controller is in the kHz range. This topic is covered in the following MathWorks tech article:

http://www.mathworks.com/company/newsletters/articles/how-modeling-helps-embedded-engineers-develop-applications-for-socs.html

/Matt

Zedboard Simulink External mode: Sample time -> real time