Simulink const block referencing changing variable doesn't update during simulation

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.

Answer 1

[C.J. Harris]

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?

[Istvan]

Thanks for the help! Unfortunately, the value still doesn't seem to update until after the simulation is over. If I set the value to '100' then at the end of the simulation the value is still 1700 (the initial value). However, during the entirety of the next simulation, the value is 100. Is that a mistake of mine, or a limitaion of Matlab?

I can't get around doing this with an event handler as the parameter is changed by a unittest case running in matlab.

[C.J. Harris]

I've not actually tried this, so I'm just speculating here, by maybe it is necessary to also call the 'update' method:

set_param(bdroot,'SimulationCommand','update')

[Istvan]

Unfortunately, that didn't work. Since this isn't related to the initial question, so I posted a new one here .