.\" Copyright (c) 1986, 1991 Regents of the University of California.
.\" %sccs.include.redist.man%
.\" @(#)tb.4 6.4 (Berkeley) %G%
.Nd line discipline for digitizing devices
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 discipline is critical in minimizing the number of samples
that would otherwise be lost due to buffer exhaustion in the
The line discipline is enabled by a sequence:
.Bd -literal -offset indent
int ldisc = TBLDISC, 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
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
changing the discipline with
calls are disabled while in tablet line-discipline mode.
The line discipline supports
requests to get/set the operating mode, and to get/set the tablet type
The line discipline supports digitizing devices which are
or Polhemus protocol formats.
For Hitachi there are several formats with that used in the
projects / unix-history / blob