TB(4)                     OpenBSD Programmer's Manual                    TB(4)

NAME
     tb - line discipline for digitizing devices

SYNOPSIS
     pseudo-device tb

DESCRIPTION
     This line discipline provides a polled interface to many common digitiz-
     ing devices which are connected to a host through a serial line.  When
     these devices stream data at high speed, the use of the line discipline
     is critical in minimizing the number of samples that would otherwise be
     lost due to buffer exhaustion in the tty(4) handler.

     The line discipline is enabled by a sequence:

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

     A typical application program then polls the digitizing device by reading
     a binary data structure which contains: the current X and Y positions (in
     the device coordinate space), up-down status of the buttons or pen sty-
     lus, 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 Polhemus 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 ioctl(2). This
     must be done before changing the discipline with TIOCSETD, as most
     ioctl(2) calls are disabled while in tablet line-discipline mode.

     The line discipline supports ioctl(2) requests to get/set the operating
     mode, and to get/set the tablet type and operating mode by or-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 sev-
     eral formats with that used in the newer model HDG-1111B the most common.

DIAGNOSTICS
     None.

SEE ALSO
     tty(4)

HISTORY
     The tb interface appeared in 4.3BSD.

OpenBSD 3.0                     March 27, 1991                               1
