How to deal with timing error when using Timer Function?

Question

sicheng 2024-7-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2134336-how-to-deal-with-timing-error-when-using-timer-function

评论： sicheng 2024-7-5

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!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Ninad 2024-7-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2134336-how-to-deal-with-timing-error-when-using-timer-function#answer_1481091

在 MATLAB Online 中打开

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

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

sicheng 2024-7-5

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

请先登录，再进行评论。