Reduce time execution in a real time serial data reading
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Hello everybody,
I'm carrying out an app that reads and plot data from sensors by serial Port. Data sent contains the values of 8 sensors plus power value and sample number. Size of the data can change because data of sensors values can changue as well. Data are sent every 0,5 s approximatly. I have to keep the data in a matrix (no problem), and plot in an axes.
If I just read values, time of each loop is fastier than the time that takes a new data to enter in the buffer, so I just have to wait for the new value, and then save it in a matrix. But If I try to plot the 8 values of the sensors, then the code takes longer than those half seconds, what makes that some data get missed. Which solution could I implement? I was thinking to save all the data but just plot one sensor in each iteration, so I'm plotting just one of each 8 values for each sensor. That's not important because after thousend of samples, visually it is impossible to see the difference, since the graph has the limit betwenn 0 and the n, where n can be +15000, but the importan thing which is save the data for processing after is performed.
But even with this last method, time of function is sometimes about 0,5 seconds and I get often an error in the matrix assignament because data collected from serial are no consistent. I was thinking play with the buffer because I could keep there more than one read, since the size is bigger than a packet of data.
The code without changes is the next one. Some ideas about how to get it? Thanks in advance.
function A = leerpuertoSerial(com,app)
hold(app.UIAxes,'on');
a = serial(com,'BaudRate',115200);
fopen(a);
A = zeros(10000,10);
n = 1;
i = 0;
cleanup = onCleanup(@()myCleanupFun(a));
ylim([0 800]);
while n<2000
if a.BytesAvailable > 0
i=i+1;
s =fscanf(a);
% I read the data packet which is something like this 1,20,343,234,234,234,543,543,543,343
C = textscan(s, '%d%d%d%d%d%d%d%d%d%d','delimiter',',');
A(i,:) = cell2mat(C);
%I plot just from the 3 value up to 10 th value (1 to 8 th sensor)
plot(app.UIAxes,i,A(i,3),'x-b');
plot(app.UIAxes,i,A(i,4),'x-b');
plot(app.UIAxes,i,A(i,5),'x-g');
plot(app.UIAxes,i,A(i,6),'x-k');
plot(app.UIAxes,i,A(i,7),'x-m');
plot(app.UIAxes,i,A(i,8),'x-c');
plot(app.UIAxes,i,A(i,9),'x-b');
plot(app.UIAxes,i,A(i,10),'x-r');
%Legends makes really slow the code.
%legend(app.UIAxes,'s1','s2','s3','s5','s6','s7','s8');
drawnow;
end
n = n+1;
flushinput(a);
end
hold(app.UIAxes,'off');
msgbox('Proceso Terminado');
xlswrite('OUTPUT',A);
end
function myCleanupFun(a)
fclose(a);
end
Answers (1)
J. Alex Lee
on 27 Feb 2020
0 votes
If instead of a loop, you use a timer (https://www.mathworks.com/help/matlab/matlab_prog/use-a-matlab-timer-object.html), you might have enough control to do what you want.
I think in general the plot is slow...if you don't need each plot to have a distinct symbol, maybe you can combine the plot into a single command. You might also save time by plotting once, and updating the XData and YData.
Another problem is that A seems to grow on every iteration, and this can slow down code especially if A is really large.
Isn't it redundant to use fscanf together with textscan? I don't know if it will affect execution time significantly, but how about fileread() instead of fscanf?
I think a better overall approach would be to decouple your data collector and displayer.
4 Comments
Carlos Molina
on 28 Feb 2020
Edited: Carlos Molina
on 28 Feb 2020
J. Alex Lee
on 28 Feb 2020
First things first, XData and YData are properties of the plotted objects, and Axes (and UIAxes) are ultimately children of a Figure (or UIFigure). So your comments on why it wouldn't work didn't make sense to me. Also, I now realize that you are keeping the plots you drew at each iteration rather than clearing them and keeping the same number of plotted objects. This is actually worse than just having each plot have lots of data points.
Stickign with the original method, does the following help at all? I think it would still slow down quite a bit as i reaches into the thousands
function A = leerpuertoSerial(com,app)
% hold(app.UIAxes,'on');
app.UIAxes.NextPlot = 'add';
app.UIAxes.YLim = [0 800];
a = serial(com,'BaudRate',115200);
fopen(a);
A = nan(10000,10);
n = 1;
i = 0;
cleanup = onCleanup(@()myCleanupFun(a));
% ylim([0 800]);
for sID = 8:-1:1
PlotHandles(sID) = plot(app.UIAxes,(1:size(A,1)),A(:,i+2),'x-');
end
legend(app.UIAxes,PlotHandles,{'s1','s2','s3','s5','s6','s7','s8'});
while n<2000
if a.BytesAvailable > 0
i=i+1;
s = filread(a);
% I read the data packet which is something like this 1,20,343,234,234,234,543,543,543,343
C = textscan(s, '%d%d%d%d%d%d%d%d%d%d','delimiter',',');
A(i,:) = cell2mat(C);
%I plot just from the 3 value up to 10 th value (1 to 8 th sensor)
for sID = 1:8
PlotHandles(sID).YData = A(:,i+2);
end
drawnow;
end
n = n+1;
flushinput(a);
end
hold(app.UIAxes,'off');
msgbox('Proceso Terminado');
xlswrite('OUTPUT',A);
end
J. Alex Lee
on 28 Feb 2020
Triggering your save+display routine with the event supplied by the serial() object seems like a good idea, but it's not clear to me what you're asking with this new scheme.
I would still think you want to trigger only data saving when data is available. You can have that data saving function trigger another event to start the display function (which hopefully my above comment can help with), and apply some interruption logic to that so you can skip displays or whatever.
If you anticipate really going into the tens of thousands of data points, you might consider resampling the data for the display to ensure that you never have more than some number of data points displayed in the screen.
Carlos Molina
on 6 Mar 2020
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on 27 Feb 2020
on 28 Feb 2020
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