MATLAB: Simulink const block referencing changing variable doesn’t update during simulation

const blocksimulink

In my Simulink diagram, I have a const block that references a global variable (lets call it myVar). I have an event handler that is called every clock tick (looks for a change in a clock block's output). That handler looks like this:
function speedRampUpUTManager(block, eventdata)
    simTime = block.OutputPort(1).Data;
      global myVar;
      if(simTime == 10)
          myVar    = 1500; //myVar is initialized to 1700
      end
      disp('myVar:');
      disp(myVar);
  end
Sure enough, during a simulation the disp shows 1700, then starts showing 1500. However, when I look at the scope attached to the const block with the Simulation Data Inspector, the value is 1700 the whole time.
My const block has the following settings:
  • Const Value: myVar
  • Interpret vector parameters as 1-D: unchecked
  • Sampling mode: Sample Based
  • Sample Time: -1
Perhaps one workaround might be:
set_param(constBlock, 'Value', 'myVar')
But I'd like to avoid that if possible.
Regards, Istvan.

Best Answer

Unfortunately unless you call 'set_param' the value of the variable will not be re-evaluated. Therefore calling 'set_param' is the way to do this. I would however recommend you find a way of doing this in Simulink instead, either via switches, or Stateflow if necessary, thereby avoiding the need for an event handler altogether.
See also: How Do I Change a Block Parameter Based on the Output of Another Block?
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