add option for splitting data into upper and lower 16 bits (fieldtrip…

…#2428)

* TYPO in comment

* ENH - allow for splitting lower and higher 16 bit

fileio/ft_read_event.m

@@ -585,7 +585,7 @@
     end
 
     try
-      % read the trigger codes from the STIM channel, usefull for (pseudo) continuous data
+      % read the trigger codes from the STIM channel, useful for (pseudo) continuous data
       % this splits the trigger channel into the lowers and highest 16 bits,
       % corresponding with the front and back panel of the electronics cabinet at the Donders Centre
       [backpanel, frontpanel] = read_ctf_trigger(filename);

fileio/private/read_trigger.m

@@ -40,7 +40,7 @@
 begsample    = ft_getopt(varargin, 'begsample'          );
 endsample    = ft_getopt(varargin, 'endsample'          );
 chanindx     = ft_getopt(varargin, 'chanindx'           ); % specify -1 in case you don't want to detect triggers
-detectflank  = ft_getopt(varargin, 'detectflank'        ); % can be up, updiff, down, downdiff, both, any, biton, bitoff
+detectflank  = ft_getopt(varargin, 'detectflank'        ); % can be up, updiff, down, downdiff, both, any, biton, bitoff, optionally appended with _split16bit
 denoise      = ft_getopt(varargin, 'denoise',      true );
 trigshift    = ft_getopt(varargin, 'trigshift',    0); % causes the value of the trigger to be obtained from a sample that is shifted N samples away from the actual flank
 trigpadding  = ft_getopt(varargin, 'trigpadding',  true );
@@ -255,9 +255,24 @@
   end
 end
 
+label = hdr.label(chanindx);
+if contains(detectflank, 'split16bit')
+  % split the trigger channel into lower and higher (bitshifted) trigger channels. 
+  % this is the same functionality as read_ctf_trigger, consider merging
+  dat_high = fix(dat / 2^16);
+  dat_low  = double(bitand(uint32(dat), 2^16-1));
+  dat      = [dat_low; dat_high];
+
+  label = cat(1, cellfun(@sprintf, repmat({'%s_low16bit'},numel(label),1), label, 'UniformOutput', false), ...
+    cellfun(@sprintf, repmat({'%s_high16bit'},numel(label),1), label, 'UniformOutput', false));
+
+  tok = tokenize(detectflank, '_');
+  detectflank = tok{1};
+end
+
 for i = 1:size(dat,1)
   % process each trigger channel independently
-  channel = hdr.label{chanindx(i)};
+  channel = label{i};
   trig    = dat(i,:);
 
   if trigpadding