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I am designing a 3 DOF control application for AR Drone (quad-rotor UAV) .. i am using multiple PID controllers to control the UAV .. these controllers are implemented by using dispatcher timer class .. for example at the start of the program I initialize the dispatcher timer like : 

        timer_yaw = new DispatcherTimer();
        timer_yaw.Interval = new TimeSpan(0, 0, 0, 0, 45);
        timer_yaw.Tick += new EventHandler(timer_yaw_tick);

as soon as the user presses a button on the GUI this timer is fired .

        timer_yaw.Start();

in timer_yaw_tick i do a little bit of processing :

    private void timer_yaw_tick(object sender, EventArgs e)
      {
            // drone commands and stuff ... basically a PD controller
            DroneData data = droneControl.NavigationData;
            PV_yaw = data.Psi;

            SP_yaw = angle;

            Error_yaw = SP_yaw - PV_yaw;

            if (Error_yaw >= 0)
                yaw_pd = 0.5f;
            else if (Error_yaw < 0)
                yaw_pd = -0.5f;


            Derivative_yaw = (Error_yaw - PreError_yaw) / Dt_yaw;

            Output_yaw = (Kp_yaw * Error_yaw) + (Kd_yaw * Derivative_yaw);

            PreError_yaw = Error_yaw;

            Output_yaw = Math.Round(Output_yaw, 1, MidpointRounding.AwayFromZero);

            Output_yaw = Output_yaw * 1000;

            t_PD_yaw = Convert.ToInt32(Output_yaw);

            // this t_PD_yaw is then sent to the drone via WiFi to make required adjustment

        }

Now in my application around 7 of these timers are running which are triggered at different time intervals....( the timer duration is mostly in milliseconds of all timers)

the problem i am facing is that my code runs fine sometimes but at times the application completely freezes i.e no response whatsoever .. its really making me go nuts and i can't seem to figure out the problem... am i using the correct timer for the job ???

Help would be really appreciated.. Thnx

Umer Qureshi
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  • where in code the debugger stops when there's a freeze ? (try several times) Could there be an issue of concurent access to Data ? The code you show *seems* to access readonly Data, but it may be in some other part. You have quite some Data Types that exists in the framework that are thread-safe, check them out (http://msdn.microsoft.com/en-us/library/dd997305.aspx) Or use a Mutex to handle conurent access by yourself. But first, just try another timer like System.Threading.Timer, it's easy :-) – GameAlchemist Aug 06 '12 at 14:00

1 Answers1

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Most likely you are using default Dispatcher which is related to the main UI thread and since DispatcherTimer is connected to Default Dispatcher - you simply overloaded UI Thread Dispatcher queue by a lot of job.

One useful test - just measure how long timer_yaw_tick() method is executed in average by putting at the start and the edn following:

// start
var watch = Stopwatch.StartNew();

// end
watch.Stop();

// see value of the watch.ElapsedMilliseconds property

I would recommend using System.Threading.Timer class for periodic job scheduling and to dispatch UI control updates to the UI thread use Dispatcher.Invoke()/Dispatcher.BeginInvoke()

sll
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