TB(4)                                                                    TB(4)



NAME
       tb - line discipline for digitizing devices

SYNOPSIS
       pseudo-device tb

DESCRIPTION
       This  line  discipline provides a polled interface to many common digi‐
       tizing devices which are connected to a host  through  a  serial  line.
       When  these devices stream data at high speed, the use of the line dis‐
       cipline is critical in minimizing the number of samples that would oth‐
       erwise be lost due to buffer exhaustion in the _t_t_y(4) handler.

       The line discipline is enabled by a sequence:

            #include <sys/tablet.h>
            int ldisc = TBLDISC, fildes; ...
            ioctl(fildes, TIOCSETD, &ldisc);

       A typical application program then polls the digitizing device by read‐
       ing a binary data structure which contains: the current X and  Y  posi‐
       tions  (in  the device coordinate space), up-down status of the buttons
       or pen stylus, proximity information (when available), and a  count  of
       the  number  of  samples  received  from  the input device since it was
       opened.  In addition, devices such as the GTCO append tilt and pressure
       information to the end of the aforementioned structure.  For the Polhe‐
       mus 3-D digitizer the structure read is completely different. Refer  to
       the include file for a complete description.

       While  in  tablet mode, normal teletype input and output functions take
       place.  Thus, if an 8 bit output data path is desired, it is  necessary
       to  prepare the output line by putting it into RAW mode using _i_o_c_t_l(2).
       This must be done before changing the discipline with TIOCSETD, as most
       _i_o_c_t_l(2) calls are disabled while in tablet line-discipline mode.

       The line discipline supports _i_o_c_t_l(2) requests to get/set the operating
       mode, and to get/set the tablet type and operating mode by  _o_r-ing  the
       two values together.

       The  line  discipline  supports digitizing devices which are compatible
       with Hitachi, GTCO, or Polhemus protocol formats.   For  Hitachi  there
       are  several  formats  with  that used in the newer model HDG-1111B the
       most common.

SEE ALSO
       tty(4)

DIAGNOSTICS
       None.



4.3 Berkeley Distribution        June 1, 1986                            TB(4)