while loop in while loop

Hi, I have a problem and i cant figure out why this code wouldnt work:

while 1
  tic;
  while(calllib('gestic', 'gestic_data_stream_update', gestic, 0)~=0)
      plot3(gestic_pos.Value.x/65533,gestic_pos.Value.y/65533,gestic_pos.Value.z/65533,'o');
      xlim([0 1]);
      ylim([0 1]);
      zlim([0 1]);
      grid();
      drawnow();
  end

    %check for abort
    if ~isempty(k)
        if strcmp(k,'s')
            disp('STOP');
            break;
        elseif strcmp(k,'p');
            disp('PAUSE');
            pause;
            k=[];
        else
            k=[];
        end
    end 

    te=toc;
    while te<0.01
        te=toc;
    end
    toc;
end

The overall while loop is executed until a certain key is pressed on the active figure. The first while reads position data from a stream and plots it. The second while should check if 10 milliseconds have passed until the loop continues.

The Problem is that MATLAB does not enter the first while loop. But when i delete the second while loop the code runs as desired.

The second while loop is needed to achieve a constant sample time.

I solved this problem by including the second while loop into the first but i dont understand why the original code doesnt work.

Can anybody explain it to me?

[Walter Roberson]

Have you tried using pause() instead of the second loop?

[Simon Hehenberger]

Thank you. This Works :) I have now rewritten my methods and its working more precise with timer objects.

I still wonder why this code with two while loops didnt work XD

[Walter Roberson]

If you were using timer objects then you would normally not pause at all; instead you would configure the timer object for constant interval for the callbacks.

Answer 1

[Niels]

As walter said try to replace

    te=toc;
    while te<0.01
        te=toc;
    end
    toc;

With

te=toc
if te<0.01
    pause(0.01-te)
end
toc