lp(7) INTERACTIVE UNIX System lp(7)
NAME
lp - parallel printer interface
DESCRIPTION
The lp driver supports both the primary printer adapter (on
the monochrome display adapter card) and secondary parallel
printer adapters simultaneously. Up to three printers are
supported. If an adapter for a printer is not installed, an
attempt to open it will fail. The close waits until all
output is completed before returning to the user. The lp
driver allows only one process at a time to write to the
adapter. If it is already busy, an open for writing will
return an error. However, the driver allows multiple opens
to occur if they are read-only.
The parallel printer adapters are character devices. The
minor device number corresponds to the primary or secondary
parallel printer adapter. Thus, minor device 0 corresponds
to the primary parallel printer adapter, while minor device
1 corresponds to the secondary adapter.
The line printer driver allows users to determine how often
the system will check whether a printer job is done and how
often the system will send a message to the console alerting
the operator that a printer needs attention. The two tun-
able parameters are:
____________________________
| Parameter | Default Value|
|___________|_______________|
| LP_POLLINT| (HZ/20) |
| LP_WARNINT| (HZ*120) |
|___________|_______________|
where the system parameter HZ (hertz) is the number of ticks
per second of the system clock (100).
This enhancement improves performance when using certain
monochrome adapter ports. Some parallel port interfaces,
such as the parallel port on many monochrome display
adapters, do not latch (retain) their interrupt signals.
This results in a loss of expected completion (READY) inter-
rupts. To prevent this loss from slowing or stopping
printer output, common code shared by the lp and slp drivers
now uses a timeout mechanism to poll the interfaces for com-
pletion. LP_POLLINT (default 1/20th of a second) defines
this polling interval.
When the printer driver detects a condition requiring opera-
tor intervention (such as paper-out), it writes a message on
the console. LP_WARNIT (default 2 minutes) defines (in
minutes) the interval between these warnings.
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lp(7) INTERACTIVE UNIX System lp(7)
These parameters may be added to your system using kconfig.
Select the option ADD TUNABLE PARAMETERS on the CONFIGURE
KERNEL menu. The system will prompt you for the parameter
name and its value.
FILES
/dev/lp*
SEE ALSO
kconfig(1).
``INTERACTIVE UNIX Operating System Maintenance Procedures''
in the INTERACTIVE UNIX Operating System Guide.
ADDED VALUE
This entry, supplied by INTERACTIVE Systems Corporation,
contains enhancements to UNIX System V.
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