TB(4)							     Kernel Interfaces Manual							     TB(4)

NAME

       tb - line discipline for digitizing devices

SYNOPSIS

       /sys/conf/SYSTEM:
	    NTB  1    # RS232 interface for Genisco/Hitachi tablets

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 tty(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 reading 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 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 neces-
       sary to prepare the output line by putting it into RAW mode using ioctl(2).  This must be done before changing the  discipline  with  TIOC-
       SETD, 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 several formats with that used in the newer model HDG-1111B the most common.

SEE ALSO

       tty(4)

DIAGNOSTICS

       None.

3rd Berkeley Distribution					  August 1, 1987							     TB(4)