Parport
The parport code provides parallel-port support under Linux. This
includes the ability to share one port between multiple device drivers.
You can pass parameters to the parport code to override its automatic
detection of your hardware. This is particularly useful if you want to
use IRQs, since in general these can’t be autoprobed successfully. By
default IRQs are not used even if they can be probed. This is
because there are a lot of people using the same IRQ for their parallel
port and a sound card or network card.
The parport code is split into two parts: generic (which deals with
port-sharing) and architecture-dependent (which deals with actually
using the port).
Parport as modules
If you load the [parport]{.title-ref}` code as a module, say:
# insmod parportto load the generic parport code. You then must load the
architecture-dependent code with (for example):
# insmod parport_pc io=0x3bc,0x378,0x278 irq=none,7,autoto tell the parport code that you want three PC-style ports, one at
0x3bc with no IRQ, one at 0x378 using IRQ 7, and one at 0x278 with an
auto-detected IRQ. Currently, PC-style (parport_pc), Sun bpp, Amiga,
Atari, and MFC3 hardware is supported.
PCI parallel I/O card support comes from parport_pc. Base I/O
addresses should not be specified for supported PCI cards since they are
automatically detected.
modprobe
If you use modprobe , you will find it useful to add lines as below to a configuration file in /etc/modprobe.d/ directory:
alias parport_lowlevel parport_pc
options parport_pc io=0x378,0x278 irq=7,automodprobe will load parport_pc (with the options
io=0x378,0x278 irq=7,auto) whenever a parallel port device driver
(such as lp) is loaded.
Note that these are example lines only! You shouldn’t in general need
to specify any options to parport_pc in order to be able to use a
parallel port.
Parport probe [optional]
In 2.2 kernels there was a module called parport_probe, which was used
for collecting IEEE 1284 device ID information. This has now been
enhanced and now lives with the IEEE 1284 support. When a parallel port
is detected, the devices that are connected to it are analysed, and
information is logged like this:
parport0: Printer, BJC-210 (Canon)The probe information is available from files in
/proc/sys/dev/parport/.
Parport linked into the kernel statically
If you compile the parport code into the kernel, then you can use
kernel boot parameters to get the same effect. Add something like the
following to your LILO command line:
parport=0x3bc parport=0x378,7 parport=0x278,auto,nofifoYou can have many parport=... statements, one for each port you want
to add. Adding parport=0 to the kernel command-line will disable
parport support entirely. Adding parport=auto to the kernel
command-line will make parport use any IRQ lines or DMA channels that
it auto-detects.
Files in /proc
If you have configured the /proc filesystem into your kernel, you will
see a new directory entry: /proc/sys/dev/parport. In there will be a
directory entry for each parallel port for which parport is configured.
In each of those directories are a collection of files describing that
parallel port.
The /proc/sys/dev/parport directory tree looks like:
parport
|-- default
| |-- spintime
| `-- timeslice
|-- parport0
| |-- autoprobe
| |-- autoprobe0
| |-- autoprobe1
| |-- autoprobe2
| |-- autoprobe3
| |-- devices
| | |-- active
| | `-- lp
| | `-- timeslice
| |-- base-addr
| |-- irq
| |-- dma
| |-- modes
| `-- spintime
`-- parport1
|-- autoprobe
|-- autoprobe0
|-- autoprobe1
|-- autoprobe2
|-- autoprobe3
|-- devices
| |-- active
| `-- ppa
| `-- timeslice
|-- base-addr
|-- irq
|-- dma
|-- modes
`-- spintime::: tabularcolumns p{13.5cm}| :::
+-----------------------------+---------------------------------------+
| File Contents | |
+=============================+=======================================+
| devices/active A li | st of the device drivers using that |
| | port. A ”+” |
+-----------------------------+---------------------------------------+
| > will appear | by the name of the device currently |
| | using |
+-----------------------------+---------------------------------------+
| > the port (it | > might not appear against any). The |
+-----------------------------+---------------------------------------+
| > string “none | ” means that there are no device |
| | drivers |
+-----------------------------+---------------------------------------+
| > using that p | ort. |
+-----------------------------+---------------------------------------+
| base-addr Para | llel port’s base address, or |
| | addresses if the port |
+-----------------------------+---------------------------------------+
| > has more tha | n one in which case they are |
| | separated |
+-----------------------------+---------------------------------------+
| > with tabs. | These values might not have any |
| | sensible |
+-----------------------------+---------------------------------------+
| > meaning for | some ports. |
+-----------------------------+---------------------------------------+
| irq Parallel | > port’s IRQ, or -1 if none is being |
| | > used. |
+-----------------------------+---------------------------------------+
| dma Parallel | > port’s DMA channel, or -1 if none |
| | > is being |
| : used. | |
+-----------------------------+---------------------------------------+
| modes Parallel | > port’s hardware modes, |
| | > comma-separated, |
| : meaning: | |
| | |
| - PCSPP | |
+-----------------------------+---------------------------------------+
| > PC-style | > SPP registers are available. |
| > | |
| > - TRISTATE | |
+-----------------------------+---------------------------------------+
| > Port is | bidirectional. |
| > | |
| > - COMPAT | |
+-----------------------------+---------------------------------------+
| > Hardware | > acceleration for printers is |
+-----------------------------+---------------------------------------+
| > availabl | e and will be used. |
| > | |
| > - EPP | |
+-----------------------------+---------------------------------------+
| > Hardware | > acceleration for EPP protocol |
+-----------------------------+---------------------------------------+
| > is avail | able and will be used. |
| > | |
| > - ECP | |
+-----------------------------+---------------------------------------+
| > Hardware | > acceleration for ECP protocol |
+-----------------------------+---------------------------------------+
| > is avail | able and will be used. |
| > | |
| > - DMA | |
+-----------------------------+---------------------------------------+
| > DMA is a | vailable and will be used. |
+-----------------------------+---------------------------------------+
| > Note that th | e current implementation will only |
| | take |
+-----------------------------+---------------------------------------+
| > advantage of line to use. | > COMPAT and ECP modes if it has an |
| | > IRQ |
+-----------------------------+---------------------------------------+
| autoprobe Any | IEEE-1284 device ID information that |
| | has been |
+-----------------------------+---------------------------------------+
| > acquired fro | m the (non-IEEE 1284.3) device. |
+-----------------------------+---------------------------------------+
| autoprobe[0-3] IEEE | > 1284 device ID information |
| | > retrieved from |
+-----------------------------+---------------------------------------+
| > daisy-chain | devices that conform to IEEE 1284.3. |
+-----------------------------+---------------------------------------+
| spintime The | number of microseconds to busy-loop |
| | while waiting |
+-----------------------------+---------------------------------------+
| > for the peri | pheral to respond. You might find |
| | that |
+-----------------------------+---------------------------------------+
| > adjusting th | is improves performance, depending on |
| | your |
+-----------------------------+---------------------------------------+
| > peripherals. | > This is a port-wide setting, i.e. |
| | > it |
+-----------------------------+---------------------------------------+
| > applies to a | ll devices on a particular port. |
+-----------------------------+---------------------------------------+
| timeslice The | number of milliseconds that a device |
| | driver is |
+-----------------------------+---------------------------------------+
| > allowed to k | eep a port claimed for. This is |
| | advisory, |
+-----------------------------+---------------------------------------+
| > and driver c | an ignore it if it must. |
+-----------------------------+---------------------------------------+
| default/* The | defaults for spintime and timeslice. |
| | When a new |
+-----------------------------+---------------------------------------+
| > port is regi | stered, it picks up the default |
| | spintime. |
+-----------------------------+---------------------------------------+
| > When a new d | evice is registered, it picks up the |
+-----------------------------+---------------------------------------+
| > default time | slice. |
+-----------------------------+---------------------------------------+
Device drivers
Once the parport code is initialised, you can attach device drivers to specific ports. Normally this happens automatically; if the lp driver is loaded it will create one lp device for each port found. You can override this, though, by using parameters either when you load the lp driver:
# insmod lp parport=0,2or on the LILO command line:
lp=parport0 lp=parport2Both the above examples would inform lp that you want /dev/lp0 to be
the first parallel port, and /dev/lp1 to be the third parallel port,
with no lp device associated with the second port (parport1). Note that
this is different to the way older kernels worked; there used to be a
static association between the I/O port address and the device name, so
/dev/lp0 was always the port at 0x3bc. This is no longer the case - if
you only have one port, it will default to being /dev/lp0, regardless
of base address.
Also:
- If you selected the IEEE 1284 support at compile time, you can say
lp=autoon the kernel command line, and lp will create devices only for those ports that seem to have printers attached.- If you give PLIP the
timidparameter, either withplip=timidon the command line, or withinsmod plip timid=1when using modules, it will avoid any ports that seem to be in use by other devices.- IRQ autoprobing works only for a few port types at the moment.
Reporting printer problems with parport
If you are having problems printing, please go through these steps to try to narrow down where the problem area is.
When reporting problems with parport, really you need to give all of the
messages that parport_pc spits out when it initialises. There are
several code paths:
- polling
- interrupt-driven, protocol in software
- interrupt-driven, protocol in hardware using PIO
- interrupt-driven, protocol in hardware using DMA
The kernel messages that parport_pc logs give an indication of which
code path is being used. (They could be a lot better actually..)
For normal printer protocol, having IEEE 1284 modes enabled or not should not make a difference.
To turn off the ‘protocol in hardware’ code paths, disable
CONFIG_PARPORT_PC_FIFO. Note that when they are enabled they are not
necessarily used; it depends on whether the hardware is available,
enabled by the BIOS, and detected by the driver.
So, to start with, disable CONFIG_PARPORT_PC_FIFO, and load
parport_pc with irq=none. See if printing works then. It really
should, because this is the simplest code path.
If that works fine, try with io=0x378 irq=7 (adjust for your
hardware), to make it use interrupt-driven in-software protocol.
If that works fine, then one of the hardware modes isn’t working
right. Enable CONFIG_FIFO (no, it isn’t a module option, and yes, it
should be), set the port to ECP mode in the BIOS and note the DMA
channel, and try with:
io=0x378 irq=7 dma=none (for PIO)
io=0x378 irq=7 dma=3 (for DMA)philb@gnu.org tim@cyberelk.net