.\"	$NetBSD: tb.4,v 1.6 2002/02/13 08:17:47 ross Exp $
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.\"     @(#)tb.4	6.4 (Berkeley) 3/27/91
.\"
.Dd March 27, 1991
.Dt TB 4
.Os
.Sh NAME
.Nm tb
.Nd line discipline for digitizing devices
.Sh SYNOPSIS
.Cd pseudo-device tb
.Sh DESCRIPTION
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
.Xr tty 4
handler.
.Pp
The line discipline is enabled by a sequence:
.Bd -literal -offset indent
#include \*[Lt]sys/tablet.h\*[Gt]
int ldisc = TABLDISC, fildes; ...
ioctl(fildes, TIOCSETD, \*[Am]ldisc);
.Ed
.Pp
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
.Tn 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.
.Pp
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
.Tn RAW
mode using
.Xr ioctl 2 .
This must be done
.Em before
changing the discipline with
.Dv TIOCSETD ,
as most
.Xr ioctl 2
calls are disabled while in tablet line-discipline mode.
.Pp
The line discipline supports
.Xr ioctl 2
requests to get/set the operating mode, and to get/set the tablet type
and operating mode by
.Em or Ns -ing
the two values together.
.Pp
The line discipline supports digitizing devices which are
compatible with Hitachi,
.Tn GTCO ,
or Polhemus protocol formats.
For Hitachi there are several formats with that used in the
newer model
.Tn HDG-1111B
the most common.
.Sh DIAGNOSTICS
None.
.Sh SEE ALSO
.Xr tty 4
.Sh HISTORY
The
.Nm
interface appeared in
.Bx 4.3 .