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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 code as a module, say

	# insmod parport

to 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,auto

to 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.

KMod

----

If you use kmod, you will find it useful to edit /etc/modprobe.conf.

Here is an example of the lines that need to be added:

	alias parport_lowlevel parport_pc

	options parport_pc io=0x378,0x278 irq=7,auto

KMod will then automatically 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,nofifo

You 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

File:		Contents:

devices/active	A list 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 port.

base-addr	Parallel port's base address, or addresses if the port

		has more than 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

				available and will be used.

		EPP		Hardware acceleration for EPP protocol

				is available and will be used.

		ECP		Hardware acceleration for ECP protocol

				is available and will be used.

		DMA		DMA is available and will be used.

		Note that the current implementation will only take

		advantage of COMPAT and ECP modes if it has an IRQ

		line to use.

autoprobe	Any IEEE-1284 device ID information that has been

		acquired from 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 peripheral to respond.  You might find that

		adjusting this improves performance, depending on your

		peripherals.  This is a port-wide setting, i.e. it

		applies to all devices on a particular port.

timeslice	The number of milliseconds that a device driver is

		allowed to keep a port claimed for.  This is advisory,

		and driver can ignore it if it must.

default/*	The defaults for spintime and timeslice. When a new

		port is	registered, it picks up the default spintime.

		When a new device is registered, it picks up the

		default timeslice.

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=0,2

or on the LILO command line:

	lp=parport0 lp=parport2

Both 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=auto' on the kernel command line, and lp will create devices

   only for those ports that seem to have printers attached.

 * If you give PLIP the `timid' parameter, either with `plip=timid' on

   the command line, or with `insmod plip timid=1' when 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:

o polling

o interrupt-driven, protocol in software

o interrupt-driven, protocol in hardware using PIO

o 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_PARPORT_PC_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