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Can anyone please tell me what is the problem.
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Tcl scripts are not automatically 'sourced' when you click the play button on the GUI.
I typically source Tcl scripts from the Tcl console. You can make the Tcl console visible using View->Utility Windows->Tcl Console.
Once you have sourced your edited Tcl script, Quartus will update the .qsf file with any new assignments your Tcl script has implemented. At that point, you can press play on the GUI and your new assignments will be used. Alternatively, the Tcl script can also 'press the play button' automatically.
There are Quartus variables that can be set to get Tcl scripts automatically run for your project. However, I haven't used that feature. Now that you know what you are looking for, you can probably find the answer in the Quartus help.
Cheers,
Dave