Using fixedRate timer in MATLAB with different data for each interval (trying to replace for loop with timer)

Question

Is there a way to have a MATLAB timer pass different data on each subsequent call to the timer function? My goal is to cycle through intervals at a fixed rate, and the pause function inside a loop is not precise enough.

I have workng MATLAB code that uses a for loop to send data via serial ports, then wait a specified time before the next iteration of the loop. The serial communication varies in speed, so if I specify 300 seconds as the period, the loop actually executes every 340-360 seconds. Here is the existing code:

clear all;
testFile = input('What is the name of the test data file (with extension): ', 's');
measurementData = csvread(testFile);
intervalDuration = input('What is the measurement change period (seconds): ');
intervalNumber = size(measurementData,2);

% Set up the COM PORT communication
sensorComPort = [101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120];
controllerComPort = [121,122,123,124];

for j=1:intervalNumber
    tic
    fprintf('\nInterval # %2d\n',rem(j,24));
    sensorMeasurementPS = [measurementData(1,j),measurementData(2,j),measurementData(3,j),measurementData(4,j),measurementData(5,j), measurementData(6,j),measurementData(7,j),measurementData(8,j),measurementData(9,j),measurementData(10,j), measurementData(11,j),measurementData(12,j),measurementData(13,j),measurementData(14,j),measurementData(15,j), measurementData(16,j),measurementData(17,j),measurementData(18,j),measurementData(19,j),measurementData(20,j)];        
    serialSensorObj = startsensorPSWithoutReset(sensorComPort, sensorMeasurementPS);
    serialSensorObj = changeMeasurement(serialSensorObj, sensorMeasurementPS); 
    rc = stopsensorPS(serialSensorObj);
    controllerMeasurementPS = [measurementData(21,j),measurementData(22,j),measurementData(23,j),measurementData(24,j)];
    serialControllerObj = startControllerPSWithoutReset(controllerComPort, controllerMeasurementPS);
    serialControllerObj = changeMeasurement(serialControllerObj, controllerMeasurementPS);
    rc2 = stopControllerPS(serialControllerObj);
    pause(intervalDuration);
    t = toc;
    fprintf('Elapsed time = %3.4f\n',t);
end

clear serialSensorObj;
clear serialControllerObj;

The serial functions are specified in other files and they are working as intended.

What I need to do is have the serial communication execute on a more precise 5-minute interval. (The actual timing of the commands inside the interval will still vary slightly, but the commands will kick off every 5 minutes over the course of 24 hours. The current version loses time and gets out of sync with another system that is reading the measurements I'm setting by serial port.)

My first thought is to use a MATLAB timer with the fixedRate execution mode, which queues the function at fixed intervals. However, it doesn't appear that I can send the timer function different data for each interval. I thought about having the timer function change a counter in the workspace, similar to j in my existing for loop, but I know that having functions interact with the workspace is not recommended.

Here's what I've come up with so far for the timer method:

function [nextJ] = changeMeasurement_fcn(obj,event,j,sensorComPort,controllerComPort)

tic
fprintf('\nInterval # %2d\n',rem(j,24));
sensorMeasurementPS = [measurementData(1,j),measurementData(2,j),measurementData(3,j),measurementData(4,j),measurementData(5,j), measurementData(6,j),measurementData(7,j),measurementData(8,j),measurementData(9,j),measurementData(10,j), measurementData(11,j),measurementData(12,j),measurementData(13,j),measurementData(14,j),measurementData(15,j), measurementData(16,j),measurementData(17,j),measurementData(18,j),measurementData(19,j),measurementData(20,j)];        
serialSensorObj = startSensorPSWithoutReset(sensorComPort, sensorMeasurementPS);
serialSensorObj = changeMeasurement(serialSensorObj, sensorMeasurementPS); 
rc = stopSensorPS(serialSensorObj);
controllerMeasurementPS = [measurementData(21,j),measurementData(22,j),measurementData(23,j),measurementData(24,j)];
serialControllerObj = startControllerPSWithoutReset(controllerComPort, controllerMeasurementPS);
serialControllerObj = changeMeasurement(serialControllerObj, controllerMeasurementPS);
rc2 = stopControllerPS(serialControllerObj);
t2 = toc;
fprintf('Elapsed time = %3.4f\n',t2);

and this is how I would call it from the main m file:

t = timer('TimerFcn',@changeMeasurement,'ExecutionMode','fixedRate','period',intervalDuration);
% then I need some code to accept the returned nextJ from the timer function

This feels a bit sloppy so I'm hoping there's a built-in way to have a timer cycle through a data set.

Another idea I had was to keep the for loop but change the pause function to use a value calculated based on how much time would add up to 5 minutes for the iteration.

To summarize my question: a) Can I have a timer pass different data to the timer function on each iteration? b) Is that a good way to go about cycling through the intervals in my data on a precise 5-minute interval?

Thanks!

Answer 1

I stumbled on this page: http://www.mathworks.com/company/newsletters/articles/tips-and-tricks-simplifying-measurement-and-timer-callbacks-with-nested-functions-new-online-support-features.html and learned that timer callback functions can be nested inside other functions (but not regular scripts).

Using that information, I cut my scenario to the basics and came up with this code:

function timerTestMain_fcn

testFile = input('What is the name of the test data file (with extension): ', 's');
testData = csvread(testFile);
intervalDuration = input('What is the voltage change period (seconds): ');
intervalNumber = size(testData,2);

t = timer('ExecutionMode','fixedRate','period',intervalDuration,'TasksToExecute',intervalNumber);

t.TimerFcn = {@timerTest_fcn};

start(t);
wait(t);
delete(t);

    function timerTest_fcn(obj,event)

        tic

        event_time = datestr(event.Data.time);
        interval_id = t.TasksExecuted;
        data_value = testData(1,interval_id);

        txt1 = 'Interval ';
        txt2 = num2str(interval_id);
        txt3 = ' occurred at ';
        txt4 = ' with data value of ';
        txt5 = num2str(data_value);

        msg = [txt1 txt2 txt3 event_time txt4 txt5];
        disp(msg)

        t2 = toc;
        fprintf('Elapsed time = %3.4f\n',t2);

    end
end

The test data file it requests must be a csv containing a row vector. For example, you could put the values 11,12,13,14,15 across the first row of the csv. The output message would then say 'Interval 1 occurred at [time] with data value of 11', 'Interval 2 occurred at [time] with data value of 12', etc.

The key is that by nesting the functions, the timer callback can reference both the test data and the timer attributes contained in the outer function. The TasksExecuted property of the timer serves as the counter.

Thanks to anyone who thought about my question. Comments welcome.