Reformat the date and time, and also show nanoseconds using mathlab

Question

Paskah Nainggolan 2011-3-21

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https://ww2.mathworks.cn/matlabcentral/answers/3619-reformat-the-date-and-time-and-also-show-nanoseconds-using-mathlab

I made a program about the moving object distance calculation,I have problem in finding time to receive and send the difference to be precise in order of nano, how to find the mathlab retrieve data with nanosecond.thx

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Answer 1

Walter Roberson 2011-3-21

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https://ww2.mathworks.cn/matlabcentral/answers/3619-reformat-the-date-and-time-and-also-show-nanoseconds-using-mathlab#answer_5251

在 MATLAB Online 中打开

You need to tell us more about the data representation.

Are these value serial date numbers? If so then

>> eps(now)
ans =
      1.16415321826935e-10
>> ans * 24*60*60
ans =
      1.00582838058472e-05

which tells you that you cannot get higher resolution than 1000 nanoseconds using that format.

If you are trying to time events using tic and toc, then you will find that those clocks are only defined down to milliseconds (1000 Hz). To go beyond that requires system-dependent methods.

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Paskah Nainggolan 2011-3-22

I'm looking for how matlab can find the time to nano-second?

The following code that I created but can not make time to nano..

function Tx_send_Callback(hObject, eventdata, handles)

TxText = get(handles.Tx_send, 'string');

fprintf(handles.serConn, TxText);

currList = get(handles.history_box, 'String');

set(handles.history_box, 'String', ...

[currList ; ['Sent = ' date(now) ': ' TxText] ]);

set(handles.history_box, 'Value', length(currList) + 1 );

set(hObject, 'String', '');

Walter Roberson 2011-3-31

Mathworks does not provide any means to time serial device events to nanoseconds. If you had the Data Acquisition Toolbox and were receiving the data with an appropriate card, you might be able to get access to higher resolution time stamps; I do not know how accurate they can go.

Recall that a nanosecond only about 2 clock cycles on a 2 GHz CPU. There is no way that an interpreted language such as MATLAB running on a multiprocessing system is going to be able to reliably interrupt and access hardware clock cycle counters within 2 instructions. For nanosecond measurements, you need a real-time device or additional hardware support.

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Answer 2

James Tursa 2011-3-22

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https://ww2.mathworks.cn/matlabcentral/answers/3619-reformat-the-date-and-time-and-also-show-nanoseconds-using-mathlab#answer_5383

在 MATLAB Online 中打开

The "now" function is only good to about 0.015 sec accuracy. You should not use it for any timing that you need more precisely than that. e.g., run this code (Ctrl-C to stop it):

n = now;
while( true )
    m = now;
    if( m ~= n )
        disp((m-n)*86400);
        n = m;
    end
end

You will have to get more precise timing some other way. e.g., if you have an OpenMP capable compiler you could get MTIMESX from the FEX and use its omp_get_wtime functionality. e.g.,

n = mtimesx('omp_get_wtime');
while( true )
    m = mtimesx('omp_get_wtime');
    if( m ~= n )
        disp(m-n);
        n = m;
    end
end

On my system the above returns differences on the order of 1.5e-5 seconds (I presume this is all system dependent), so maybe something like this will work for you. MTIMESX (which admittedly is overkill for your situation) can be found here:

http://www.mathworks.com/matlabcentral/fileexchange/25977-mtimesx-fast-matrix-multiply-with-multi-dimensional-support