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.