MATLAB Programming/Psychtoolbox/KbCheck

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A changed kbcheck that will check all connected keyboards and will sort out some invalid devices that appear to be keyboards.

It should be noted that this script will stop and return on the first keyboard that has a key that is pressed. Perhaps this could be modified so that the sum of all checked keyboards is returned and so if you are pressing a key on one keyboard you can also be pressing another key on another keyboard and get both responses.

function [keyIsDown,secs, keyCode] = KbCheck(deviceNumber)
% [keyIsDown,secs,keyCode] = KbCheck([deviceNumber])
% Return keyboard status (keyIsDown), time (secs) of the status check, and
% keyboard scan code (keyCode).
%    keyIsDown      1 if any key, including modifiers such as <shift>,
%                   <control> or <caps lock> is down. 0 otherwise.
%    secs           time of keypress as returned by GetSecs.
%    keyCode        Mac: a 128-element logical array.  Each bit within the
%                   logical array represents one keyboard key. If a key is
%                   pressed, its bit is set, othewise the bit is clear. To
%                   convert a keyCode to a vector of key numbers use
%                   FIND(keyCode). To find a key's keyNumber use KbName
%                   or KbDemo.
%                   Win: a 256-element array. It seems that the first
%                   128 elements correspond to the
%                   ascii sequence of the characters, and may be consistent
%                   with the Mac key codes.
% KbCheck and KbWait determine whether any key is down now, including the
% meta keys: <caps lock>, <shift>, <command>, <control>, and <option>. The
% only key not reported is the start key (triangle) used to power on your
% computer.
% GetChar and CharAvail are character-oriented (and slow), whereas KbCheck
% and KbWait are keypress-oriented (and fast). If only a meta key was hit,
% KbCheck will return true, because a key was pressed, but CharAvail will
% return false, because no character was generated. See GetChar.
% KbCheck and KbWait are MEX files, which take time to load when they're
% first called. They'll then stay loaded until you flush them (e.g. by
% changing directory or calling CLEAR MEX).
% OS X: ___________________________________________________________________
% KbCheck uses the PsychHID function, a general purpose function for
% reading from the Human Interface Device (HID) class of USB devices.
% OS 9: ___________________________________________________________________
% Command-Period causes an immediate exit.
% The Mac OS Event Manager detects and queues typed characters in the
% background. GetChar will return any characters typed before the  call to
% GetChar. FlushEvents can be used to clear the character event  buffer
% read by GetChar. Unlike GetChar, KbCheck only reports keys  depressed at
% the moment KbCheck is called.  FlushEvents has no effect  on KbCheck.
% Hitting CapsLock makes KbCheck and KbWait think that you're holding the
% shift key down. They will continue to think so (returning 1) until you
% release the shift by hitting CapsLock again.
% KbCheck and KbWait detect that a key is down by using the low-level Mac
% OS call GetKeys. It's not clear what temporal accuracy this provides, but
% it's much better than going through the higher-level Event Manager. Our
% impression from reading the documentation in Dan Costin's KeMo package
% web
% <> is that this
% low-level call still has uncertainty on the order of 11 ms because of the
% way the Mac OS polls ADB devices. Someone clever could probably use his
% advice to develop MEX files that timed keypresses more  accurately than
% KbCheck does.
% _________________________________________________________________________
% See also: FlushEvents, KbName, KbDemo, KbWait, GetChar, CharAvail, KbDemo.

% TO DO:
%  - Mention that on USB systems there the USB bus is sampled at 100hz
%  - We could augment this to to accept an optional keyboard device number.

% 3/6/97  dhb  Wrote it.
% 8/2/97  dgp  Explain difference between key and character.
% 1/28/98 dgp  Explain CapsLock.
% 2/4/98  awi  Explain keyCode.
% 2/13/98 awi  Changed keyCode to logical array, pointers to KbDecode, KbExplore.
% 2/19/98 dgp  Shortened by moving some text to GetChar.m.
% 3/15/99 xmz  Added comment for Windows version.
% 6/23/00 awi  Added paragraph contrasting queuing of GetChar and KbCheck.
% 7/7/00  dgp  Cosmetic.
% 6/17/02 awi  ****** OS X-specific fork from the OS 9 version *******
%                Added conditional invocation of PsychHID on OSX
% 7/12/04 awi  Cosmetic.  Separted platform-specific help. Use IsOSX now.
% 7/13/05 rpk  Added ability to sort out invalidProducts that were
%                   considered keyboards. Also, will now check all
%                   valid keyboards insted of just the first one. 
keyIsDown = 0;
if IsOSX
    if nargin==1
        [keyIsDown,secs, keyCode]= PsychHID('KbCheck', deviceNumber);
    elseif nargin == 0
        invalidProducts = {'USB Trackball'};
        devices = PsychHID('devices');
        for i = 1:length(devices)
            if(strcmp(devices(i).usageName, 'Keyboard') )
                for j = 1:length(invalidProducts)
                    if(~(strcmp(invalidProducts{j}, devices(i).product)))
                            [keyIsDown,secs, keyCode]= PsychHID('KbCheck', i);

    elseif nargin > 1
        error('Too many arguments supplied to KbCheck');