How to deal with timing error when using Timer Function?

Hi everyone,

I am currently writing a code using Timer function to record mouse path with 1kHz rate (i.e. I want to record the position of the mouse every 0.001s). I discovered that the Timer function does not have the precision under 50ms. I also found that the matlab time outputs did not add up to the total trial running time (i.e. if I add up the time tracked by the Timer function, the value is always less than the actual running time of the mouse path). I think if the error in timing comes from the accumulation of excution time of the Timer function, in theory the value should be greater than the actual running time. I am hoping if anyone could take a look at my code and give me some suggestion, and am also wondering if people have encountered similar issue. The following is the Timer Function that I used:

timerObj = timer('TimerFcn', @recordMousePos, 'Period', 0.001, 'ExecutionMode', 'fixedRate');

Thank you!

Answer 1

[Ninad]

Hi Sicheng,

You can use the "get" MATLAB function to achieve your goal. This MATLAB function retrieves the current position of the mouse pointer (cursor) on the screen.

In the following command:

loc = get(0, 'PointerLocation');

• The first argument (0) refers to the root object (the entire screen), and the second argument ('PointerLocation') specifies the property we want to retrieve.
• The property 'PointerLocation' returns a 2-element vector [x, y], where x and y represent the horizontal and vertical coordinates of the mouse pointer, respectively.

I have written a dummy code where you can use the get function to track the cursor on the screen:

flag = 0;

while true
    loc = get(0, 'PointerLocation');
    if (flag==0)
        prev_locx = loc(1);
        prev_locy = loc(2);
        flag=1;
    end

    new_locx = loc(1);
    new_locy = loc(2);
    
    if (new_locy~=prev_locy) || (new_locx~=prev_locx)
        fprintf('Mouse position: X = %d, Y = %d\n', loc(1), loc(2));
        prev_locx = new_locx;
        prev_locy = new_locy;
    end
    
    pause(0.001);  % Pause for 1 ms (adjust as needed)
end

Please go through the following MathWorks documentation to know more about the "get" function:

https://www.mathworks.com/help/matlab/ref/get.html

Regards,

Ninad

[sicheng]

Thank you for your reply.

However, I have tried other methods before, such as using tictoc to accurately time 1ms while recording events, but they didn't work. I am actually a little skeptical about whether errors in such a small time scale are inevitable, because as long as the program is called, these errors will exist.

“tic;

period = 0.001; % 1ms

while ishandle(fig) && cyclesCompleted < maxCycles

if toc >= period

recordMousePos();

tic;

end

pause(0.001);

end”

Regards，

Sicheng