.po 1i
.TH LP 4 Zilog
.ad
.fi
.po 1i
.V 08/15/84 17:30:54
.\" @[$]lp.4	1.5	08/15/84 17:30:54 - Zilog Inc.
.ad
.SH NAME
lp \- line printer driver
.SH DESCRIPTION
The files
.BR lp ,
.BR lp2 
refer to line printer ports.
.PP
ZEUS can accommodate up to three line printers, depending
on the hardware configuration.
The printers can have either a Centronics or Data Products interface.
During SYSGEN the kernel
can be configured to have no line printers.
.PP
The default configuration is for Centronics line printer.
A Data Products interface will need a different hardware configuration.
Refer to the System 8000 hardware reference manual for details.
.PP
The device files
.IR /dev/lp 
and
.IR /dev/lp2
refer to the line printer drivers.
Each has a major device number of 9 and a minor device number
that depends on the kind of printer and port used.
.PP
The line printers are accessed by the line printer spooler 
.BR lp (1) 
or by the 
.BR ioctl (2) 
system call.
.PP
The 
.BR ioctl 
system call is used to modify some parameters of the line
printer driver.
This call uses the following structure and commands 
which are defined in 
.sp
.IR /usr/include/sgtty.h:
.nf
.sp
.br
 #define	SHOWLPR   (('l' << 8) | 0)
 #define	SETLP     (('l' << 8) | 1)
.sp
 /*
 * This is the structure of the 
 * arguments to the lpr ioctl program
 */
.sp
 struct lparms
.sp
 {
.sp
     int     lines;         /* number of lines per page     */
     int     cols;          /*number of columns per page    */
     int     indent;        /*default indentation for       */
                            /*line printer                  */
.sp
 };
.fi
.PP
The way the the system call is implemented is 
similar to the tty(2) ioctl
call.
.sp
.nf
 #include <sgtty.h>
.sp
 struct lparms args ;
.sp
	if ((fd = open("/dev/lp", 2)) < 0 )
		printf("can\'t open /dev/lp\\n");
	rtn = (ioctl(fd, SHOWLPR, &args));
	rtn = (ioctl(fd, SETLP, &args));
.sp
.fi
.PP
If the command SHOWLPR is issued to the line 
printer, the line printer driver
will return to the user's lparms structure the parameters:
lines per page, columns per page, and standard indent.
.PP
Lines per page is defined as the number of lines printed before
an FF character (0xC) is output.
.PP
Columns per page means the number of characters 
printed before a "carriage
return" is output.
For Data Products printers this is a '\\n' character (0xA) which causes
a line feed and carriage return to be emitted.
For Centronics printers the line printer driver must emit a '\\r' (0xD) 
and '\\n' (0xA) to emit a carriage return and line feed.
If the Centronics printer has an "automatic line feed" option,
it emits a line feed for '\\r' (0xD).
This should be disabled to allow underlining.
.PP
Indent is the default indentation for all output to 
.IR /dev/lp.
Note that the the length of the line printed will be cols \- indent 
thus lines longer than this are truncated rather than 
shifted to the right.
.PP
The command SETLP allows the system administrator to set these values 
in the line printer driver to accommodate printers with different 
characteristics.
The default values set at compile time for lines, cols and indent 
are 66, 130, and 1 respectively.
.PP
The following is a description of how the line printer driver handles 
some special characters.
.br
\& '\\n' (0xA) \- Newline:  This is output 'as is' for 
Data Products printers.
For Centronics printers, a '\\r' is output also.
.br
\& '\\r' (0xD) \- Carriage Return:  This is output 'as is'.
.br
\& '\\f' (0xC) \- Form Feed:  This output 'as is' for 
Data Products printers
and appended with a '\\r' for Centronics printers.
.br
\& '\\b' (0x8) \- Backspace:  A '\\r' is 
emitted and spaces are printed up 
to the previous character printed.
.br
\& '\\t' (0x9) \- Horizontal Tab:  Blanks are output to the 
nearest multiple 
of four.
.SH FILES
/dev/lp
.br
/dev/lp2
.br
/usr/include/sgtty.h
.SH SEE ALSO
ioctl(2),
tty(4).
.sp
.I Zeus System Administrators Manual, 
.br
.I System 8000 Hardware Reference Manual Manual
.SH LIMITATIONS
There is no way at this time of choosing CR/LF default for automatic LF
printers.