Sample time of sfunction that needs long to execute

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Hendrik Lorenz
Hendrik Lorenz 2019-8-15
评论： Hendrik Lorenz 2019-8-16
I want to run a simulink model on an external device (code generation, external mode) to do model predictive control (MPC). My simulink model contains an sfunction that takes N*Ts time to execute (Ts: sample time) and compute a new control trajectory. However I want to run my model on the external device with the sampling time Ts. Therefore I want the MPC sfunction to be executed every (N+1)*Ts, because it needs N*Ts to calculate new controls. In the meanwhile I want to output the "old" control trajectory every Ts.
My question:
  • How can I run the sfunction at a different sample time than the rest of the model, while ensuring that the simulink model won't crash because it is waiting for an output from the sfunction while it is still calculating but instead outputting the old trajectory?
  • How can I hold the old control trajectory in my simulink model?
Further information:
  • Used MPC packages: ACADO, GRAMPC
  • External device: Quanser QUBE Servo 2
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Joel Handy
Joel Handy 2019-8-15
Essentially, simulink runs all of the blocks that occur during a time step to completion before moving onto the next timestep. So with the rate transition block, although that function may be running at a much lower frequency (1 out of every N steps), it wont run in the background as the rest of the model continues on without it. You will simply have one time step out of N that takes N*Ts seconds to complete.
Hendrik Lorenz
Hendrik Lorenz 2019-8-16
Ah I see, thanks! Quanser apparently supplies a server client solution for communication between different simulink models that then could run on different sample times I guess. Unfortunately I do not have the required license and time to look into this right now.

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回答（1 个）

Hendrik Lorenz
Hendrik Lorenz 2019-8-15
编辑：Hendrik Lorenz 2019-8-15
I managed to give different sampling time to the sfunction block as documented here:
https://de.mathworks.com/help/simulink/sfg/sample-times-cpp.html
under Block-Based Sample Times
I had to add some rate transition blocks to account for the different sampling times.
If I run now on my device it gives outputs, however in my Simulink i do not see my measured data in the scopes anymore. Seems like just the last value is displayed. Also the time down in the right corner stays at 0.0 now. Any advice?

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