Tune “VariableName” of “From Workspace” block

Hello, I’m building a realtime app with simulink (Simulink Realtime + App Designer) and I want to be able to tune the data loaded by a “From Workspace” block before running the model. The issue is the block parameter is non-tunable so I get the following warning: “Parameter ‘VariableName’ of ‘Model’ is non-tunable but refers to tunable variables”… I read here (https://it.mathworks.com/help/slrealtime/ug/tuning-block-parameters-and-model-parameters.html) that one can tune non-tunable block parameters defining Simulink objects, which is exactly what I’m doing but it’s not working. Can anyone help? Thank you.

Answer 1

[Fangjun Jiang]

"Tune" usually means to change the value while the simulation is running, like a Gain value. What you need doesn't sound like "tune", but rather change the variable name before the simulation starts. To do that, you can use set_param('FromBlockPath','VariableName','MyVariable')

Or, you can change the value of the variable in the workspace, but not to change the variable name of the From Workspace block.

[Enzo Yacometti]

That’s correct. I have defined a variable and I want to modify the value of it before doing a run (in real time). My issue arises because the Speedgoat target computer cannot see that parameter to be changed in its Parameter Table, due to the fact that the block parameter is by definition non-tunable. So how can I proceed? Basically I want to be able to use the “setparam” function with the target but it’s not able to see the parameter.

[Enzo Yacometti]

The variable in question is in a data dictionary linked to the model, and running the model in “normal mode” works perfectly. Now my issue is accessing that variable to update its value from the target computer before running in real time. I have done this already with a variant condition variable and constant blocks, but with the “From Workspace” block I haven’t been able to.

[Fangjun Jiang]

In that case, the From Workspace block might not be the right block to use. You might be able to use a Lookup Table block or in the simple case, a Constant block.

[Enzo Yacometti]

Then I would ask for your help on how to do it. The array that I’m working with is a column of time + 30 columns of signals, so that they’re fed into the model as inputs over time. With a constant block I would be feeding static data… Ideally what I’m trying to replicate is a “From Spreadsheet” block that feeds the data as input to my model but that’s not compatible with Simulink RT… Do you have any idea of how to achieve this? In other words, how to update an array (with time and signals) inside a data dictionary from my target computer to be fed into my model?

[Fangjun Jiang]

Ok, I see.

1. You want to build this model to run in Speedgoat so every time you can pick a different set of input data without re-build the model. set_param() won't work because it requires re-build. The only way is to use a tunable parameter.
2. What you need is a 1-D lookup. Look at the current time, match the time in the input data and output the corresponding value.
3. Usually, a 1-D Lookup Table block can do this. But I just tried, it can only lookup one column. So you would need 30 blocks for 30 columns. It is unlike the interp1() function in MATLAB, where you can use one time vector but 30 column of data. You can run the function once to get 30 outputs.
4. So I have two suggestions, none is ideal. One is to use 30 1-D Lookup Table blocks. The second one is to use a MATLAB Function block to implement the function that is similar to interp1(), where you find the current time, which is an input (generated by the Clock block), then match the time in your first column and output the value of second to 31st column. It can be done, The data can be defined as a parameter of the MATLAB Function block. If the height of one set of data is different than the other set of data, you might need to define the parameter as variable size, which poses a little more difficulites.
5. Ask the Mathworks tech support to see if they have better solutions, and post it here if you find one.

[Enzo Yacometti]

Thank you I have adopted the interp1 solution and seems to work, though it may cause unnecessary computational load… I hope this is something that can be resolved in future releases because few blocks of this nature are compatible with simulink RT and choosing input data on a realtime app is quite a basic task. In any case, thank you!

[Paul]

Regarding point 3 above, I think you can can use a single 2-D lookup table block.

The table data in the block is the 30-column 2D matrix where each row of the matrix correspond to the same value of the independent variable.

The first set of breakpoints are the breakpoints of the independent variable.

The second set of breakpoints are just 1:30.

The first port input to the block is the time-varying independent variable.

The second port input to the block is the output of a Constant block with constant value being 1:30 (or any other way to implement a constant value on a signal line).

Note: I'm pretty sure that the 2D lookup table block takes the first variable down the rows and the second variable across the columns as reflected by my suggestion (which is the opposite of the convention used for interp2). But double check this.

[Enzo Yacometti]

Thank you. I wasn’t aware I could pass an array as breakpoint input to a LUT to get an array as output. Cheers!

[Fangjun Jiang]

@Paul, brilliant!