Timer error: Cannot start timer because it is already running.

I am trying to implement a simple timer in a GUI. It is just a figure with two buttons. I want when I press the start button to execute the updaterFcn callback function of timer. When I push the stop button I want the timer to stop. That's all. However, I get the following error (and I don't know why):

Error while evaluating StartFcn for timer 'timer-2' 

Cannot start timer because it is already running.

This is my function

function stopwatch

S.fh = figure('units','pixels',...
              'position',[300 300 400 400],...
              'menubar','none',...
              'name','stopwatch',...
              'numbertitle','off');

S.pb(1) = uicontrol('style','push',...
                    'units','pixels',...
                    'position',[10 10 85 30],...
                    'fontsize',14,...
                    'string','start',...
                    'CallBack',@switchon);
S.pb(2) = uicontrol('style','push',...
                    'units','pixels',...
                    'position',[105 10 85 30],...
                    'fonts',14,...
                    'str','stop',...
                    'CallBack',@switchoff);

tmr = timer('Period',1,...  
            'TimerFcn',@updater,...
            'StopFcn',@switchoff,...
            'StartFcn',@switchon);

      function updater(varargin)
          disp('Timer!')
      end
      function switchon(varargin)
          start(tmr)

      end
      function switchoff(varargin)
          stop(tmr)
  %         delete(tmr)
      end

Answer 1

[per isakson]

There are two problems with your timer:

• The values of StopFcn causes stop(tmr) in switchoff to call stop a second time and correspondingly with StartFcn
• ExecutionMode must be set to get more than one call by the timer

Try to replace your timer definition by

    tmr = timer( 'Period'       , 1             ...
               , 'BusyMode'     , 'drop'        ...
               , 'ExecutionMode', 'fixedDelay'  ...
               , 'TimerFcn'     , @updater      );

[Giorgos Papakonstantinou]

Thank you per isakson!