Why do I get an error saying Global declaration not resolved to Data Store Memory using global variables in my MATLAB Function block?"
MATLAB: Do I get an error using global variables in the MATLAB Function block
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Related Solutions
The issue arises because there is a clash between a global and a local data store. The Simulink.Signal object 'Temp' in the Data Dictionary defines a global Data Store because it can be accessed by all models in the hierarchy. Thus, the Data Store Memory block in the main model is now redundant because it also declares a local data store named 'Temp'.
You can find more information about the creation and application of Data Stores on the following page of the documentation page:
In particular, the final sentence of the section 'Create and Apply Data Stores' should clarify this issue.
To resolve the error and continue with the simulation, you can remove the Data Store Memory block, and then Simulink will automatically read and write to the 'Temp' variable defined in the Data Dictionary. You will notice that the Data Store Read and Write blocks will show that 'Temp' is a global Data Store.
To generate code without an extra copy of the variable, you will have to change some settings. Here are the steps to follow:
1) Open the "Ports and Data Manager" as follows: Double click the "MATLAB function" block to open the function in MATLAB. In the top toolbar, select "Edit Data" found in the "Simulink" section.
2) In the "Ports and Data Manager" dialog window, change myDataStore to be a Data Store instead of an input to the MATLAB function block.
3) Declare myDataStore as a global inside the MATLAB function as follows:
>> global myDataStore;4) Wrap myDataStore inside a call to coder.ref:
>> coder.ceval('-global','myCFunction', coder.ref(myDataStore));You can refer to the following documentation page for more information about "coder.ref":
5) Comment out the "Data Store Memory Read" block that is currently connected to the "MATLAB function" block.
6) Double click the "Data Store Memory" block and go to the signal attributes tab. The signal type cannot be set to "auto". Change it accordingly. For example:
7) Now you can generate code without the extra copy of the variable.
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Best Answer
The Diagnostic Viewer may say something like "Global declaration not resolved to a Data Store Memory block registered via the Ports and Data Manager."
In MATLAB Functions in Simulink, global declarations are not mapped to the MATLAB global workspace. To use global data in your MATLAB Function block, or in any code that this block calls, you must:
(a) Declare a global variable in your MATLAB Function block, or in any code that is called by the MATLAB Function block.
(b) Register a Data Store Memory block or Simulink.Signal object that has the same name as the global variable with the MATLAB Function block.
For reference see: https://www.mathworks.com/help/releases/R2018b/simulink/ug/using-global-data-with-the-matlab-function-block.html#bshotv6-1
If using the Data Store Memory block approach a few things to note are:
(1) In the Ports and Data Manager you may need to manually create the data entry, and change the name to match the Data Store Memory block, and set the scope to Data Store Memory.
(2) You will need to specify Dimensions, Signal type (real/complex), and Data type (e.g. double) for the variable in the corresponding Data Store Memory block.
(3) The initial value will be determined by the Initial value setting given in the Data Store Memory block. Variables of the same name in for example the Base Workspace are ignored.