freebsd-skq/share/man/man4/lpt.4

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.\" Copyright (c) 1993 Christopher G. Demetriou
.\" Copyright (c) 1994 Geoffrey M. Rehmet
.\" Copyright (c) 1999 Nicolas Souchu
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.Dd February 14, 1999
.Dt LPT 4
.Os
.Sh NAME
.Nm lpt
.Nd generic printer device driver
.Sh SYNOPSIS
.Cd "device ppc"
.Cd "device ppbus"
.Cd "device lpt"
.Sh DESCRIPTION
The current
.Em lpt
driver is the port of the original lpt driver to the
.Xr ppbus 4
system.
.Pp
One purpose of this port was to allow parallel port sharing with other
parallel devices.
Secondly, inb()/outb() calls have been replaced by ppbus
function calls.
lpt is now arch-independent thanks to the ppbus interface.
See
.Xr ppbus 4
for more info about the ppbus system.
.Pp
The parallel port bus is allocated by lpt when the printer device is opened
and released only when the transfer is completed: either when the device
is closed or when the entire buffer is sent in interrupt driven mode.
.Pp
The driver can be configured to be either interrupt-driven, or
to poll the printer.
Ports that are configured to be
interrupt-driven can be switched to polled mode by using the
.Xr lptcontrol 8
command.
.Pp
Depending on your hardware, extended capabilities may be configured with the
.Xr lptcontrol 8
command.
With an ECP/ISA port, you can take advantage
of FIFO and DMA.
.Pp
In order to retrieve printer info from /dev/lpt0, just apply the
.Nm cat
command to the device.
If the printer supports IEEE1284 nibble mode and has
data to send to the host, you will get it.
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /dev/lpt0
first parallel port driver
.El
.Sh SEE ALSO
.Xr ppbus 4 ,
.Xr ppc 4 ,
.Xr lptcontrol 8
.Sh HISTORY
This driver replaces the functionality of the lpa
driver, which is now defunct.
.Sh BUGS
There are lots of them, especially in cheap parallel port implementations.
.Pp
It is only possible to open a lpt port when a printer is connected and
on-line, making it impossible to run
.Xr lptcontrol 8
when there is no printer connected.
.Pp
This driver could still stand a rewrite.