NAME
    KBD_READMATRIX -- Read the current keyboard key matrix.

FUNCTION
    This function reads the up/down state of every key in the
    key matrix.

IO REQUEST INPUT
    io_Message      mn_ReplyPort set if quick I/O is not possible
    io_Device       preset by the call to opendevice
    io_Command      KBD_READMATRIX
    io_Flags        IOB_QUICK set if quick I/O is possible
    io_Length       the size of the io_Data area in bytes: this
                    must be big enough to hold the key matrix.
    io_Data         a buffer area to fill with the key matrix:
                    an array of bytes whose component bits reflect
                    each keys state: the state of the key for
                    keycode n is at bit (n MOD 8) in byte
                    (n DIV 8) of this matrix.

IO REQUEST OUTPUT
    io_Error
         IOERR_BADLENGTH - the io_Length was not exactly 13 bytes.
                    The buffer is unchanged.  This is only returned
                    by V33/V34 kickstart.
    io_Actual       the number of bytes filled in io_Data with key
                    matrix data, i.e. the minimum of the supplied
                    length and the internal key matrix size.

NOTE
    For V33/V34 Kickstart, io_Length must be set to exactly 13 bytes.

RESULTS
    This function sets the error field in the iorequest, and sets
    matrix to the current key matrix.