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NAME    [Toc]    [Back]

     tb - line discipline for digitizing devices

SYNOPSIS    [Toc]    [Back]

     pseudo-device tb [count]

DESCRIPTION    [Toc]    [Back]

     This line discipline provides a  polled  interface  to  many
common digitizing
  devices  which are connected to a host through a serial
line.  When
     these devices stream data at high speed, the use of the line
     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 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 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

     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.

     Calling read(2) on the device always succeeds, returning the
last sample,
     although the select(2) and poll(2) system  calls  will  correctly report the
     read state for new samples.

     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.

DIAGNOSTICS    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]


HISTORY    [Toc]    [Back]

     The tb interface appeared in 4.3BSD.

OpenBSD     3.6                          March      27,      1991
[ Back ]
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