View source for Programming Tutorial:Working with the FieldTrip buffer

==Getting the data in Matlab==

The FieldTrip buffer is a multi-threaded and network transparent buffer that allows data to be streamed to it by BCI2000, while at the same time allowing a seperate MATLAB session on the same or another computer to read data from the buffer for analysis. Besides writing the data, BCI2000 also writes the changed status variables as events.

To use the FieldTrip buffer, you start BCI2000 with the FieldTripBuffer as the Signal Processing application. Subsequently you start MATLAB yourself, i.e. your MATLAB session is a normal standalone application. You should have a recent copy of the FieldTrip toolbox installed, or at least a copy of the FieldTrip fileio module. The FieldTrip toolbox and its components are available for download from http://www.ru.nl/neuroimaging/fieldtrip. Please make sure that the correct version of the fileio module is on your MATLAB search path.

Subsequently you can do something like the following code below. You should be able to copy and paste the code into the MATLAB command window and get a real-time updating MATLAB figure with the data from BCI2000.

<pre>
filename = 'buffer://localhost:1972';

% read the header for the first time to determine number of channels and sampling rate
hdr = ft_read_header(filename, 'cache', true);

count      = 0;
prevSample = 0
blocksize  = hdr.Fs;
chanindx   = 1:hdr.nChans;

while true
  % determine number of samples available in buffer
  hdr = ft_read_header(filename, 'cache', true);

  % see whether new samples are available
  newsamples = (hdr.nSamples*hdr.nTrials-prevSample);

  if newsamples>=blocksize

    % determine the samples to process
    begsample  = prevSample+1;
    endsample  = prevSample+blocksize ;

    % remember up to where the data was read
    prevSample  = endsample;
    count       = count + 1;
    fprintf('processing segment %d from sample %d to %d\n', count, begsample, endsample);

    % read data segment from buffer
    dat = ft_read_data(filename, 'header', hdr, 'begsample', begsample, 'endsample', endsample, 'chanindx', chanindx);

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % subsequently the data can be processed, here it is only plotted
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    % create a matching time-axis
    time = (begsample:endsample)/hdr.Fs;

    % plot the data just like a standard FieldTrip raw data strucute
    plot(time, dat);

    % ensure tight axes
    xlim([time(1) time(end)]);

    % force Matlab to update the figure
    drawnow

  end % if new samples available
end % while true
</pre>