4.2. The parport device (kernels >= 2.1.33)
4.2. The parport device (kernels >= 2.1.33)
Beginning with kernel 2.1.33 (and available as a patch for kernel
2.0.30), the lp device is merely a client of the new parport
device. The addition of the parport device corrects a number of
the problems that plague the old lp device driver - it can share
the port with other drivers, it dynamically assigns available
parallel ports to device numbers rather than enforcing a fixed
correspondence between I/O addresses and port numbers, and so
forth.
The advent of the parport device has enabled a whole flock of new
parallel-port drivers for things like Zip drives, Backpack CD-ROMs
and disks, and so forth. Some of these are also available in
versions for 2.0 kernels; look around on the web.
The main difference that you will notice, so far as printing goes,
is that parport-based kernels dynamically assign lp devices to
parallel ports. So what was lp1 under Linux 2.0 may well be lp0
under Linux 2.2. Be sure to check this if you upgrade from an
lp-driver kernel to a parport-driver kernel.
The most popular problems with this device seems to stem from
misconfiguration:
- The Distribution
-
Some GNU/Linux distributions don't ship with a properly setup /etc/modules.conf (or /etc/conf.modules), so the driver isn't loaded properly when you need it to be. With a recent
modutils, the proper magical lines from modules.conf seem to be:
alias /dev/printers lp # only for devfs?
alias /dev/lp* lp # only for devfs?
alias parport_lowlevel parport_pc # missing in Red Hat 6.0-6.1
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- The BIOS
-
Many PC BIOSes will make the parallel port into a Plug-and-Play device. This just adds needless complexity to a
perfectly simple device that is nearly always present; turn
off the PnP setting for your parallel port ("LPT1" in many
BIOSes) if your parallel port isn't detected by the Linux
driver. The correct setting is often called "legacy", "ISA",
or "0x378", but probably not "disabled".
You can also read the parport documentation in your kernel sources, or
look at the parport web
site.
