lp Device Driver lp
Line printer driver
Files /dev/lp* access the line-printer's device drivers for IBM
AT COHERENT. The drivers are assigned major device number 3.
The COHERENT system supports three printers, in both cooked and
raw modes. The following gives the device name, minor device,
and I/O port:
/dev/lpt1 0 0x3BC (/etc/mknod /dev/lpt1 c 3 0)
/dev/lpt2 1 0x378 (/etc/mknod /dev/lpt2 c 3 1)
/dev/lpt3 2 0x278 (/etc/mknod /dev/lpt3 c 3 2)
/dev/rlp1
t1
28 0x3BC (/etc/mknod /dev/rlpt1 c 3 128)
/dev/rlp1
t29 0x378 (/etc/mknod /dev/rlpt2 c 3 129)
/dev/rlp1
t30 0x278 (/etc/mknod /dev/rlpt3 c 3 130)
``Cooked'' processing processes the special characters BS (back-
space), HT (horizontal tab), LF (line feed), FF (form feed), and
CR (carriage return) appropriately; raw processing simply passes
them on to the printer.
The driver uses a hybrid busy-wait/timeout discipline to support
printers efficiently that have varying buffer sizes in a multi-
tasking environment.
The kernel variable LPWAIT is the time during that the processor
waits for the printer to accept the next character. If the
printer is not ready within the LPWAIT time period, the then
processor resumes normal processing for the number of ticks set
by LPTIME Thus, setting LPWAIT to a very large number (e.g.,
30,000) and LPTIME to a very small number (e.g., one) results in
a fast printer, but slow processing on other tasks. Conversely,
setting LPWAIT to a small number (e.g., 50) and LPTIME to a large
number (e.g., five) result in efficient multi-tasking, but also
results in a slow printer unless the printer itself contains a
buffer (as is presently normal with all except the least expen-
sive printers). By default, LPWAIT is set to 100 and LPTIME to
four. We recommend that you set LPWAIT to no less than 50, and
LPTIME to no less than one.
***** Files *****
/dev/lp* -- ``Cooked'' printer interfaces
/dev/rlp* -- Raw printer interfaces
***** See Also *****
ascii, device drivers, epson, lpr
COHERENT Lexicon Page 1