  The Linux Plug-and-Play-HOWTO
  David S.Lawyer
   <mailto:dave@lafn.org>
  v0.09, 7 January 2000

  Help with understanding and dealing with the complex Plug-and-Play
  issue.  How to get your Linux system to support Plug-and-Play.
  ______________________________________________________________________

  Table of Contents
























































  1. Introduction

     1.1 Copyright, Trademarks, Disclaimer, & Credits
        1.1.1 Copyright
        1.1.2 Disclaimer
     1.2 Future Plans; You Can Help
     1.3 New Versions of this HOWTO

  2. What PnP Should Do: Allocate "Bus-Resources"

     2.1 What is Plug-and-Play (PnP)?
     2.2 How a Computer Finds Devices (and conversely)
     2.3 I/O Addresses, etc.
     2.4 IRQs --Overview
     2.5 DMA Channels
     2.6 Memory Ranges
     2.7 "Resources" to both Device and Driver
     2.8 The Problem
     2.9 PnP Finds Devices Plugged Into Serial Ports

  3. The Plug-and-Play (PnP) Solution

     3.1 Introduction to PnP
     3.2 How It Works (simplified)
     3.3 Starting Up the PC
     3.4 Buses
     3.5 Linux Needs to Cope Better with PnP

  4. Configuring a PnP BIOS

     4.1 Do you have a PnP operating system?
        4.1.1 Interoperability with Windows9x
     4.2 How are bus-resources to be controlled?
     4.3 Reset the configuration?

  5. How to Deal with PnP Cards

     5.1 Introduction to Dealing with PnP Cards
     5.2 Disable PnP ?
     5.3 BIOS Configures PnP
        5.3.1 Intro to Using the BIOS to Configure PnP
        5.3.2 The BIOS's ESCD Database
        5.3.3 Using Windows to set the ESCD
        5.3.4 Adding a New Device (under Linux or Windows)
     5.4 Isapnp (part of isapnptools)
     5.5 PCI Utilities
     5.6 Patch the Kernel to Make Linux PnP
     5.7 Windows Configures
     5.8 Device Driver Configures
     5.9 PnP Software/Documents

  6. Tell the Driver the Configuration

     6.1 Introduction
     6.2 Serial Port Driver: setserial
     6.3 Sound Card Drivers
        6.3.1 OSS-Lite
        6.3.2 OSS (Open Sound System) and ALSA

  7. What Is My Current Configuration?

     7.1 How Are My Device Drivers Configured?
     7.2 How Are My Hardware Devices Configured?

  8. Appendix

     8.1 Addresses
        8.1.1 ISA Bus Configuration Address (Read-Port etc.)
        8.1.2 Address ranges
        8.1.3 Address space
        8.1.4 Range Check (ISA Testing for IO Address Conflicts)
        8.1.5 Communicating Directly via Memory
     8.2 Interrupts --Details
     8.3 PCI Interrupts
     8.4 Isolation


  ______________________________________________________________________

  1.  Introduction

  1.1.  Copyright, Trademarks, Disclaimer, & Credits

  1.1.1.  Copyright

  Copyright (c) 1998, 1999 by David S. Lawyer.

  Please freely copy and distribute (sell or give away) this document in
  any format.  Forward any corrections and comments to the document
  maintainer.  You may create a derivative work and distribute it
  provided that you:


  1. Send your derivative work (in the most suitable format such as
     sgml) to the LDP (Linux Documentation Project) or the like for
     posting on the Internet.  If not the LDP, then let the LDP know
     where it is available.  Except for a translation, send a copy to
     the previous maintainer's url as shown in the latest version.

  2. License the derivative work in the spirit of this license or use
     GPL.  Include a copyright notice and at least a pointer to the
     license used.

  3. Give due credit to previous authors and major contributors.

  If you're considering making a derived work other than a translation,
  it's requested that you discuss your plans with the current
  maintainer.


  1.1.2.  Disclaimer

  Much of the info in this HOWTO was obtained from the Internet,
  implications in books that may be in error or obsolete, etc.  While I
  haven't intentionally tried to mislead you, there are likely a number
  of errors in this document.  Please let me know about them.  Since
  this is free documentation, it should be obvious that I cannot be held
  legally responsible for any errors.


  1.2.  Future Plans; You Can Help

  Please let me know of any errors in facts, opinions, logic, spelling,
  grammar, clarity, links, etc.  But first, if the date is over a month
  old, check to see that you have the latest version.  Please send me
  any info that you think belongs in this document.

  I haven't studied in detail neither isapnptools nor David Howells'
  patches to the kernel (but I plan to).  Nor do I fully understand how
  PnP is configured by the BIOS (it depends on which BIOS) nor how
  Windows9x updates the ESCD.  Thus this HOWTO is still incomplete and
  may be inaccurate (let me know where I'm wrong).  In this HOWTO I've
  sometimes used ??  to indicate that I don't really know the answer.


  1.3.  New Versions of this HOWTO

  New versions of the Plug-and-Play-HOWTO should appear every month or
  so and will be available to browse and/or download at LDP mirror
  sites.  For a list of mirror sites see:
  <http://metalab.unc.edu/LDP/mirrors.html>.  Various formats are
  available.  If you only want to quickly check the date of the latest
  version look at:  <http://metalab.unc.edu/LDP/HOWTO/Plug-and-Play-
  HOWTO.html>.  The version you are now reading is: v0.08, 28 November
  1999.


  2.  What PnP Should Do: Allocate "Bus-Resources"

  2.1.  What is Plug-and-Play (PnP)?

  Oversimplified, Plug-and-Play automatically tells the software (device
  drivers) where to find various pieces of hardware (devices) such as
  modems, network cards, sound cards, etc.  Plug-and-Play's task is to
  match up physical devices with the software (device drivers) that
  operates them and to establish channels of communication between each
  device and its driver.  In order to achieve this, PnP allocates the
  following "bus-resources" to both drivers and hardware: I/O addresses,
  IRQ's, DMA channels (ISA bus only), and memory regions.  If you don't
  understand what these 4 bus-resources are read the following
  subsections of this HOWTO.  An article in Linux Gazette about 3 of
  these bus-resources is Introduction to IRQs, DMAs and Base Addresses
  Once these bus-resources have been assigned (and if the correct driver
  is installed), the names for such devices in the /dev directory are
  ready to use.

  This PnP assignment of bus-resources is sometimes called "configuring"
  but it is only a low level type of configuring.  Even with PnP fully
  utilized, much configuring of devices is done by other than PnP.  For
  example, for modem configuration an "init string" is sent to the modem
  over the I/0 address "channel".  This "init string" has nothing to do
  with PnP although the "channel" used to send it to the modem was
  allocated by PnP.  Setting the speed (and many other parameters) of a
  serial port is done by sending messages to the device driver from
  programs run by the user (often automatically boot-time).  This
  configuring also has nothing to do with PnP.  Thus when talking about
  PnP "configuring" means only a certain type of configuring.  While
  other documentation (such a for MS Windows) simply calls bus-resources
  "resources",  I have coined the term "bus-resources" so as to
  distinguish it from the multitude of other kinds of resources.


  2.2.  How a Computer Finds Devices (and conversely)

  A computer consists of a CPU/processor to do the computing and memory
  to store programs and data.  In addition, there are a number of
  devices such as various kinds of disk-drives, a video card, a
  keyboard, network cards, modem cards, sound cards, serial and parallel
  ports, etc.  There is also a power supply to provide electric energy,
  various buses on a motherboard to connect the devices to the CPU, and
  a case to put all this into.

  In olden days most all devices had their own plug-in cards (printed
  circuit boards).  Today, in addition to plug-in cards, many "devices"
  are small chips permanently mounted on the "motherboard".  Cards which
  plug into the motherboard may contain more than one device.  Memory
  chips are also sometimes considered to be devices but are not plug-
  and-play in the sense used in this HOWTO.
  For the computer system to work right, each device must be under the
  control of its "device driver".  This is software which is a part of
  the operating system (perhaps loaded as a module) and runs on the CPU.
  Device drivers are associated with "special files" in the /dev
  directory although they are not really files.  They have names such as
  hda1 (first partition on hard drive a), ttyS0 (the first serial port),
  eth1 (the second ethernet card), etc.  To make matters more
  complicated, the particular device driver selected, say for eth1, will
  depend on the type of ethernet card you have.  Thus eth1 can't just be
  assigned to any ethernet driver.  It must be assigned to a certain
  driver that will work for the type of ethernet card you have
  installed.  To control a device, the CPU (under the control of the
  device driver) sends commands (and data) to and reads info from the
  various devices.  In order to do this each device driver must know the
  address of the device it controls.  Knowing such an address is
  equivalent to setting up a communication channel, even though the
  physical "channel" is actually the data bus inside the PC which is
  shared with almost everything else.

  The communication channel is actually a little more complex than
  described above.  An "address" is actually a range of addresses and
  there is a reverse part of the channel (known as interrupts) which
  allows devices to send an urgent "help" request to their device
  driver.


  2.3.  I/O Addresses, etc.

  PC's have 3 address spaces: I/O, main memory, and configuration (only
  on the PCI bus).  All of these 3 types of addresses share the same
  address bus inside the PC.  But the voltage on certain dedicated wires
  on the PC's bus tells which "space" an address is in: I/O, main
  memory, or configuration.  See ``Addresses'' for more details.
  Devices were originally located in I/O address space although today
  they may use space in main memory.  An I/0 address is sometimes just
  called "I/O", "IO", "i/o" or "io".  The term "I/O port" also used.
  There are two main steps to allocate the I/O addresses (or other bus-
  resources such as interrupts):


  1. Set the I/O address, etc. on the card (in one of its registers)

  2. Let its device driver know what this I/O address, etc. is


  The two step process above is something like the two part problem of
  finding someone's house number on a street.  You must obtain (and
  write down) the house number and someone must install a number on the
  front of the house so that it may be found.  In computers, the device
  driver must obtain the address and the device hardware must get the
  same address set in one of its registers.  Both of these must be done,
  but some people make the mistake of doing only one of these and then
  wonder why the computer can't find the device.  For example, they will
  use "setserial" to assign an address to a serial port without
  realizing that this only tells the driver an address.  It doesn't set
  the address in the serial port hardware itself.  If the serial port
  actually had a different address (or none at all) and you told
  setserial wrong, then you're in trouble.

  Another obvious requirement is that before the device driver can use
  an address it must be first set on the card.  Since device drivers
  often start up soon after you start the computer, they sometimes try
  to access a card (to see if it's there, etc.) before the address has
  been set in the card by a PnP configuration program.  Then you see an
  error message that they can't find the card even though it's there
  (but doesn't yet have an address).
  What was said in the last 2 paragraphs regarding I/O addresses applies
  with equal force to other bus-resources: ``IRQs --Overview'', ``DMA
  Channels'', and ``Memory Regions''.  What theses are will be explained
  in the next 3 sections.


  2.4.  IRQs --Overview

  After reading this you may read ``Interrupts --Details'' for some more
  details.  The following is intentionally oversimplified:  Besides the
  address, there is also an interrupt number to deal with (such as IRQ
  5).  It's called an IRQ (Interrupt ReQuest) number.  We already
  mentioned above that the device driver must know the address of a card
  in order to be able to communicate with it.  But what about
  communication in the opposite direction?  Suppose the the device needs
  to tell its device driver something immediately?  For example, the
  device may have just received a lot of bytes destined for main memory
  and the device needs to call its driver to fetch these bytes at once
  and transfer them from the device's nearly full buffer into main
  memory.

  How should the device call for help?  It can't use the main data bus
  since it's likely already in use.  Instead it puts a voltage on an
  dedicated interrupt wire (part of the bus) which is often reserved for
  that device alone.  This signal is called an interrupt.  There are the
  equivalent of 16 such wires in a PC and each wire leads (indirectly)
  to a certain device driver.  Each wire has a unique IRQ (Interrupt
  ReQuest) number.  The device must put its interrupt on the correct
  wire and the device driver must listen for the interrupt on the
  correct wire.  Which wire it's put on is determined by the IRQ number
  stored in the device.  This same IRQ number must be known to the
  device driver so that the device driver knows which IRQ line to listen
  to.

  Once the device driver gets the interrupt (a call for help) it must
  find out why the interrupt was issued and take appropriate action to
  service the interrupt.  On the ISA bus each device needs its own
  unique IRQ number.  For the PCI bus and other special cases the
  sharing of IRQs is allowed.


  2.5.  DMA Channels

  DMA channels are only for the ISA bus.  DMA stands for "Direct Memory
  Access".  This is where a device is allowed to take over the main
  computer bus from the CPU and transfer bytes directly to main memory.
  Normally the CPU would make such a transfer in a two step process: 1.
  reading from the I/O memory space of the device and putting these
  bytes into the CPU itself  2. writing these bytes from the CPU to main
  memory.  With DMA it's usually a one step process of sending the bytes
  directly from the device to memory.  The device must have such
  capabilities built into its hardware and thus not all devices can do
  DMA.  While DMA is going on the CPU can't do too much since the main
  bus is being used by The DMA transfer.

  The PCI bus doesn't really have any DMA but instead it has something
  even better: bus mastering.  It works something like DMA and is
  sometimes called DMA (for example, hard disk drives that call
  themselves "UltraDMA").  It allows devices to temporarily become bus
  masters and to transfer bytes almost like the bus master was the CPU.
  It doesn't use any channel numbers since the organization of the PCI
  bus is such that the PCI hardware knows which device is currently the
  bus master and which device is requesting to become a bus master.
  Thus there is no allocation of DMA channels for the PCI bus.


  When a device on the ISA bus wants to do DMA it issues a DMA-request
  using dedicated DMA request wires much like an interrupt request.  DMA
  actually could have been handled by using interrupts but this would
  introduce some delays so it's faster to do it by having a special type
  of interrupt known as a DMA-request.  Like interrupts, DMA-request are
  numbered so as to identify which device is making the request.  This
  number is called a DMA-channel.  Since DMA transfers all use the main
  bus (and only one can run at a time) they all actually use the same
  channel but the "DMA channel" number serves to identify who is using
  the "channel".  Hardware registers exist on the motherboard which
  store the current status of each "channel".  Thus in order to issue a
  DMA-request, the device must know its DMA-channel number which must be
  stored in a register on the physical device.


  2.6.  Memory Ranges

  Some devices are assigned address space in main memory.  It's often
  "shared memory" or "memory-mapped I/O".  Sometimes it's ROM memory on
  the device.  When discussing bus-resources it's often just called
  "memory".  Such a device might also use I/O address space.

  When you plug in such a card, you are in effect also plugging in a
  memory module for main memory.  This memory can either be ROM (Read
  Only Memory) or shared memory.  Shared memory is shared between the
  device and the CPU (running the device driver).  This memory can serve
  as a means of direct data "transfer" between the device and main
  memory.  It's not really a transfer since the device puts data into
  its own memory on its card which also happens to be in main memory.
  Both the card and the device driver need to know where it is.  The
  memory address are likely to be very high so that they do not conflict
  with the lower addresses of the memory chips in your computer.

  ROM is different.  It is likely a program (perhaps a device driver)
  which will be used with the device.  Hopefully, it may work with Linux
  and not just Windows ??  It may need to be shadowed which means that
  it is copied to your main memory chips in order to run faster.  Once
  it's shadowed it's no longer "read only".


  2.7.  "Resources" to both Device and Driver

  Thus device drivers must be "attached" in some way to the hardware
  they control.  This is done by supplying bus-resources (I/O, Memory,
  IRQ's, DMA's) to both the physical device and the device driver
  software.  For example, a serial port uses only 2 (out of 4 possible)
  resources: an IRQ and an I/O address.  Both of these values must be
  supplied to the device driver and the physical device.  The driver
  (and its device) is also given a name in the /dev directory (such as
  ttyS1).  The address and IRQ number is stored by the physical device
  in registers on the card (or in a chip on the motherboard).  For the
  case of jumpers, this info is always stored in the device hardware (on
  the card, etc.).  But for the case of PnP, the register data is
  usually lost when the PC is powered down (turned off) so that the
  resource data must be supplied to each device anew each time the PC is
  powered on.


  2.8.  The Problem

  The architecture of the PC provides only a limited number of IRQ's,
  DMA channels, I/O address, and memory regions.  If there were only
  several devices and they all had standardized bus-resource (such as
  unique I/O addresses and IRQ numbers) there would be no problem of
  attaching device drivers to devices.  Each device would have a fixed
  resources which would not conflict with any other device on your
  computer.  No two devices would have the same addresses, there would
  be no IRQ conflicts, etc.  Each driver would be programmed with the
  unique addresses, IRQ, etc. hard-coded into the program.  Life would
  be simple.

  But it's not.  Not only are there so many different devices today that
  conflicts are frequent, but one sometimes needs to have more than one
  of the same type of device.  For example, one may want to have a few
  different disk-drives, a few serial ports, etc.  For these reasons
  devices need to have some flexibility so that they can be set to
  whatever address, IRQ, etc. is needed to avoid conflicts.  But some
  IRQ's and addresses are pretty standard such as the ones for the clock
  and keyboard.  These don't need such flexibility.

  Besides the problem of conflicting allocation of bus-resources, there
  is a problem of making a mistake in telling the device driver what the
  bus-resources are.  For example, suppose that you enter IRQ 4 in a
  configuration file when the device is actually set at IRQ 5.  This is
  another type of bus-resource allocation error.

  The allocation of bus-resources, if done correctly, establishes
  channels of communication between physical hardware and their device
  drivers.  For example, if a certain I/O address range (resource) is
  allocated to both a device driver and a piece of hardware, then this
  has established a one-way communication channel between them.  The
  driver may send commands and info to the device.  It's actually a
  little more than one-way since the driver may get information from the
  device by reading it's registers.  But the device can't initiate any
  communication this way.  To initiate the device needs an IRQ in order
  to create a two-way communication channel where both the driver and
  the device can initiate communication.


  2.9.  PnP Finds Devices Plugged Into Serial Ports

  External devices that connect to the serial port via a cable (such as
  external modems) can also be called Plug-and-Play.  Since only the
  serial port itself needs bus-resources (an IRQ and I/O address) there
  are no bus-resources to allocate to such plug-in devices.  Thus PnP is
  not really needed for them.  Even so, there is a PnP specification for
  such external serial devices.

  A PnP operating system will find such an external device and read its
  model number, etc.  Then it may be able to find a device driver for it
  so that you don't have to tell an application program that you have a
  certain device on say /dev/ttyS1.  Since you should be able to
  manually inform your application program (via a configuration file,
  etc.) what serial port the device is on (and possibly what model
  number it is) you should not really need this "serial port" feature of
  PnP.


  3.  The Plug-and-Play (PnP) Solution

  3.1.  Introduction to PnP

  The term Plug-and-Play (PnP) has various meanings.  In the broad sense
  it is just auto-configuration where one just plugs in a device and it
  configures itself.  In the sense used in this HOWTO, the configuration
  is only that of configuring PnP bus-resources and letting the device
  drivers know about it.  In a more narrow sense it just setting bus-
  resources in the hardware devices.  It may also mean the PnP
  specifications which (among other things) specify how PnP resource
  data is to be read and written to devices (often cards) on the ISA
  bus.  The standard PCI (and not PnP) specifications do the same for
  the PCI bus.
  PnP matches up devices with their device drivers and specifies their
  communication channels.  On the ISA bus before Plug-and-Play the bus-
  resources were set in hardware devices by jumpers.  Software drivers
  were assigned bus-resources by configuration files (or the like) or by
  probing the for the device at addresses where it's expected to reside.
  The PCI bus was PnP-like from the beginning so it was trivial to
  implement PnP for this bus.  Since the PCI bus specifications don't
  use the term PnP it's not clear whether or not the PCI bus should be
  called PnP (but it supports in hardware what today is called PnP).


  3.2.  How It Works (simplified)

  Here's an oversimplified view of how PnP works.  The PnP configuration
  program (perhaps a program in the BIOS) finds all PnP devices and asks
  each what bus-resources it needs.  Then it checks what bus-resources
  (IRQs, etc.) it has to give away.  Of course if it has reserved bus-
  resources used by non-PnP (legacy) devices (if it knows about them) it
  doesn't give these away.  Then it uses some criteria (not specified by
  PnP specifications) to give out the bus-resources so that there are no
  conflicts and so that all devices get what they need (if possible).
  It then tells each physical device what bus-resources are assigned to
  it and the devices set themselves up to use only the assigned bus-
  resources.  Then the device drivers somehow find out what bus-
  resources their devices use and are thus able to communicate
  effectively with the devices they control.

  For example, suppose a card needs one interrupt (IRQ number) and 1 MB
  of shared memory.  The PnP program reads this request from the card.
  It then assigns the card IRQ5 and 1 MB of memory addresses space,
  starting at address 0xe9000000.  It's not always this simple as the
  card may specify that it can only use certain IRQ numbers (ISA only)
  or that the 1 MB of memory must lie within a certain range of
  addresses.  The details are different for the PCI and ISA buses with
  more complexity on the ISA bus.

  There are some shortcuts that PnP software may use.  One is to keep
  track of how it assigned bus-resources at the last configuration (when
  the computer was last used) and reuse this.   Windows9x and PnP BIOSs
  do this but standard Linux doesn't.  Windows9x stores this info in its
  "Registry" on the hard disk and a PnP BIOS stores it in non-volatile
  memory in your PC (known as ESCD; see ``The BIOS's ESCD Database'').

  Under Linux it's each device for itself and there is no centralized
  non-volatile registry of resource assignments.  Some device drivers
  store the last configuration they used and use it next time the
  computer is powered on.  They implicitly assume that the rest of the
  hardware will not need to use it's bus-resources.

  If the device hardware remembered their previous configuration, then
  there wouldn't be any hardware to configure at the next boot-time, but
  they seem to forget their configuration when the power is turned off.
  Some devices contain a default configuration (but not necessarily the
  last one used).  Thus a PnP configuration program needs to be run each
  time the PC is powered on.  Also, if a new device has been added, then
  it too needs to be configured.  Allocating bus-resources to this new
  device might involve taking some bus-resources away from an existing
  device and assigning the existing device alternative bus-resources
  that it can use instead.


  3.3.  Starting Up the PC

  When the PC is first turned on the BIOS chip runs its program to get
  the computer started (the first step is to check out the hardware).
  If the operating system is stored on the hard-drive (as it normally
  is) then the BIOS must know about the hard-drive.  If the hard-drive
  is PnP then the BIOS may use PnP methods to find it.  Also, in order
  to permit the user to manually configure the BIOS's CMOS and respond
  to error messages when the computer starts up, a screen (video card)
  and keyboard are also required.  Thus the BIOS must PnP-configure
  these devices on its own.

  Once the BIOS has identified the hard-drive, the video card, and the
  keyboard it is ready to start booting (loading the operating system
  into memory from the hard-disk).  If you've told the BIOS that you a
  have a PnP operating system (PnP OS), it should start booting the PC
  as above and let the operating system finish the PnP configuring.
  Otherwise, a PnP-BIOS will (prior to booting) likely try to do the
  rest of the PnP configuring of devices (but not their drivers).


  3.4.  Buses

  ISA is the old bus of the old IBM PC's while PCI is a newer and faster
  bus from Intel.  The PCI bus was designed for what is today called
  PnP.  It makes it easy (as compared to the ISA bus) to find out how
  PnP bus-resources have been assigned to hardware devices.  To see what
  has happened look at the /proc/pci "file" (/proc/bus/pnp/devices for
  kernel 2.2+), the boot-up messages on your display (use shift-PageUp
  to back up), or use PCI Utilities (for kernel 2.2+).

  For the ISA bus there is a real problem with implementing PnP since no
  one had PnP in mind when the ISA bus was designed and there are almost
  no I/O addresses available for PnP to use for sending configuration
  info to physical device.  As a result, the way PnP was shoehorned onto
  the ISA bus is very complicated.  A whole book has been written about
  it.  See ``PnP Book''.  Among other things, it requires that each PnP
  device be assigned a temporary "handle" by the PnP program so that one
  may address it for PnP configuring.  Assigning these "handles" is call
  "isolation".  See ``Isolation'' for the complex details.

  Eventually, the ISA bus should become extinct.  When it does, PnP will
  be easier since it will be easy to find out how the BIOS has
  configured the hardware.  There will still be the need to match up
  device drivers with devices and also a need to configure devices that
  are added when the PC is up and running.  These needs would be
  satisfied if Linux was a PnP operating system.


  3.5.  Linux Needs to Cope Better with PnP

  PnP (for the ISA bus) was invented by Compaq, Intel, and Phoenix.
  Microsoft has been a leading promoter of it.  Linux would have been
  better off if PnP had never been "invented".  Eventually the ISA bus
  will have become extinct and the PnP-like PCI bus will prevail so that
  we will have in effect gotten an easy-to-implement PnP.  But like it
  or not, most all new ISA hardware today is PnP and Linux has no choice
  but to deal effectively with PnP.  But standard Linux (as of early
  1999) makes dealing with PnP complicated (especially on the ISA bus)
  while the purpose of PnP was to make it simple.

  In a sense, Linux is already somewhat PnP for the PCI bus.  When the
  PC starts up you may note from the messages on the screen that some
  Linux device drivers often find their hardware devices (and the bus-
  resources the BIOS has assigned them).  But there are situations that
  a PnP operating system could handle better: 1. A shortage of bus-
  resources 2. More than one driver for a physical device  3. An
  activated driver which can't find it's physical device 4. Hot
  installation of a device (docking, etc.)


  Linux users should not need to delve into the details of PnP to
  configure ISA PnP devices as they now need to.  One solution would be
  a standardized version of the Linux kernel that supports Plug-and-Play
  on the ISA, PCI, and other buses.  A patch to the kernel has been
  written although most drivers don't support it.  It's not part of
  standard Linux.  See ``Patch Kernel''.


  4.  Configuring a PnP BIOS

  When the computer is first turned on, the BIOS runs before the
  operating system is loaded.  Newer BIOSs are PnP and will configure
  some or all of the PnP devices.  For most PnP BIOSs there is no way to
  disable PnP so you have to live with it.  Here are some of the choices
  which may exist in your BIOS's CMOS menu:


  o  ``Do you have a PnP operating  system?''

  o  ``How are bus-resources to be controlled?''

  o  ``Reset the configuration?''


  4.1.  Do you have a PnP operating system?

  If you say yes, then the PnP BIOS will PnP-configure the hard-drive,
  video card, and keyboard to make the system bootable.  But it will
  leave it up to the operating system to finish the configuration job.
  It may do an ``Isolation'' on the ISA bus leaving the devices disabled
  but ready to be configured by the operating system.  For Linux you
  should probably tell it that you don't have a PnP operating system.
  If you don't do this, the BIOS might leave the ISA devices it hasn't
  configured in a disabled state ??  Also PCI devices might not get
  configured ??

  If you tell the BIOS you don't have a PnP OS, then the BIOS will do
  the configuring itself.  Unless you have added new PnP devices, it
  should use the configuration which it has stored in its non-volatile
  memory (ESCD).  See ``The BIOS's ESCD Database'' If the last session
  on your computer was with Linux, then there should be no change in
  configuration.  See ``BIOS Configures PnP''.  But if the last session
  was with Windows9x (which is PnP) then Windows could have modified the
  ESCD.  It supposedly does this only if you "force" a configuration or
  install a legacy device.  See ``Using Windows to set ESCD''.  If you
  are using the isapnp or PCI Utilities program(s) to do configuring,
  they will run after the BIOS runs and change things the way you told
  them to.


  4.1.1.  Interoperability with Windows9x

  If you are running both Linux and Windows on the same PC, how do you
  answer the BIOS's question: Do you have a PnP OS?  Normally (and
  truthfully) you would say no for standard Linux and yes for Windows9x.
  But it's a lot of bother to have to set up the BIOS's CMOS menu
  manually each time you want to switch OSs.  One solution is set the
  CMOS for no PnP OS, including when you start Windows.  One might
  expect that Windows would be able to handle this situation where it is
  presented hardware that has been fully configured by the BIOS.  In
  addition, one might expect that even if Windows didn't realize that
  the hardware was already configured, it would redo this configuration
  and then work OK.  But it doesn't seem to work this way.  It seems
  that Windows may just tell its device drivers what has been stored in
  the Windows' Registry.  But the actual hardware configuration (done by
  the BIOS) is what was stored in the ESCD and may not be the same as
  the Registry => trouble.

  One way to try to get the Registry and the ESCD the same is to install
  (or reinstall) Windows when the BIOS is set for "not a PnP OS".  This
  should present Windows with hardware configured by the BIOS.  If this
  configuration is without conflicts, Windows will hopefully leave it
  alone and save it in it's Registry.  Then the ESCD and the registry
  are in sync.  If this works for you (and this is the latest version of
  this HOWTO), let me know as I only have one report of this working out
  OK.

  Another method is to "remove" devices that are causing problems in
  Windows by clicking on remove in the Device Manager.  Then reboot with
  "Not a PnP OS" (set it in the CMOS as you start to boot).  Windows
  will then reinstall the devices, hopefully using the bus-resource
  settings configured by the BIOS.  Be warned that Windows will likely
  ask you to insert the Window installation CD since it sometimes can't
  find the driver files (and the like) even thought they are still
  there.  As a test I "removed" the NIC card which had a Novell
  compatible drivers.  Upon rebooting, Windows reinstalled it with
  Microsoft networking instead of Novell.  This meant that the Novell
  Client needed to be reinstalled.  Let me know about your problems with
  this method (only if this is the latest version of this HOWTO).


  4.2.  How are bus-resources to be controlled?

  This may involve just deciding how to allocate IRQ and DMA bus-
  resources.  If set to "auto", the BIOS will do the allocation.  If set
  to manual, you manually reserve some IRQ's for use on "legacy" (non-
  pnp) cards.  The BIOS may or may not otherwise know about your legacy
  cards.  The BIOS will only know about your legacy cards if you ran ICU
  (or the like) under Windows to tell the BIOS about them.  If the BIOS
  knows about them, then try using "auto".  If it doesn't know about
  them then manually reserve the IRQ's needed for the legacy ISA cards
  and let the rest be for the BIOS PnP to allocate.


  4.3.  Reset the configuration?

  This will erase the BIOSs ESCD data-base of how your PnP devices
  should be configured as well as the list of how legacy (non-PnP)
  devices are configured.  Never do this unless you are convinced that
  this data-base is wrong and needs to be remade.  It was stated
  somewhere that you should do this only if you can't get your computer
  to boot.  If the BIOS loses the data on legacy devices, then you'll
  need to run ICA again under DOS/Windows to reestablish this data.


  5.  How to Deal with PnP Cards

  5.1.  Introduction to Dealing with PnP Cards

  Today most all new internal boards (cards) are Plug-and-Play (PnP).
  Although some software exists in Linux to handle PnP, it is not always
  easy to use.  There are 6 different methods listed below to cope with
  PnP (but some may not be feasible in your situation).  Which one(s)
  you should use depends on your goals.  What may be most expedient to
  do now may not be the easiest and best in the long run.  A seemingly
  simple way is to do nothing and just let a PnP-BIOS configure it but
  then you may need to do some exploring to to find out what the BIOS
  has done.  A comparison of these methods needs to be written by
  someone who has tried them all.  You may need to use more than one
  method to do the job.


  o  ``Disable PnP''  by jumpers or DOS/Windows software (but many cards
     can't do this)

  o  ``BIOS Configures PnP'' (For the PCI bus you only need a PCI BIOS,
     otherwise you need a PnP BIOS)

  o  ``Isapnp'' is a program you can always use to configure PnP devices
     on the ISA bus only

  o  ``PCI Utilities'' is for configuring the PCI bus

  o  ``Windows Configures'' and then you boot Linux from within
     Windows/DOS.  Use as a last resort

  o  ``Patch Kernel'' to transform Linux into a PnP operating system

  o  ``Device Driver Configures'' but few do

  Any of the above will set the bus-resources in the hardware.  But only
  the last two should tell device driver what it's done.  Only the last
  one definitely tells the driver (since it is the driver).  How the
  driver gets informed depends on the driver and you may need to do
  something to inform it.  See ``Tell the Driver the Configuration''


  5.2.  Disable PnP ?

  Many devices are PnP only with no option for disabling PnP.  But for
  some, you may be able to disable PnP by jumpers or by running a
  Windows program that comes with the device (jumperless configuration).
  This will avoid the often complicated task of configuring PnP.  Don't
  forget to tell the BIOS that these bus-resources are reserved.  There
  are also some reasons why you might not want to disable PnP:


  1. If you have MS Windows on the same machine, then you may want to
     allow PnP to configure devices differently under Windows from what
     it does under Linux.

  2. The range of selection for IRQ numbers (or port addresses) etc.
     may be quite limited unless you use PnP.

  3. You might have a Linux device driver that uses PnP methods to
     search for the device it controls.

  4. If you need to change the configuration in the future, it may be
     easier to do this if it's PnP (no setting of jumpers or running a
     Dos/Windows program).

  5. You may have (or will have) other PnP devices that need configuring
     so that you'll need to provide for (or learn about) PnP anyway.

     Once configured as non-PnP devices, they can't be configured by PnP
     software or the BIOS (until you move jumpers and/or use the
     Dos/Windows configuration software again).


  5.3.  BIOS Configures PnP

  5.3.1.  Intro to Using the BIOS to Configure PnP

  If you have a PnP BIOS, it can configure the hardware.  This means
  that your BIOS reads the resource requirements of all devices and
  configures them (allocates bus-resources to them).  It is a substitute
  for a PnP OS except that the BIOS doesn't match up the with their
  devices nor tell the drivers how it has done the configuring.  It
  should normally use the configuration it has stored in its non-
  volatile memory (ESCD).  If it finds a new device or if there's a
  conflict, the BIOS should make the necessary changes to the
  configuration and will not use exactly what was in the ESCD.

  Your BIOS must support such configuring but there have been cases
  where it doesn't do it correctly or completely.  An advantage of using
  the BIOS is that it's simple since in most cases there is nothing to
  set up (except to tell the BIOS's CMOS menu it's not a PnP OS).  While
  some device drivers may be able to automatically detect what the BIOS
  has done, in some cases you'll need to determine it (not always easy).
  See ``What Is My Current Configuration?'' Another possible advantage
  is that the BIOS does its work before Linux starts so that all the
  bus-resources are ready to be used (and found) by the device drivers
  that start up later.

  According to MS it's only optional (not required) that a PnP BIOS be
  able to PnP-configure the devices (without help from MS Windows).  But
  it seems that most of the ones made after 1996 ?? or so can do it.  We
  should send them thank-you notes if they do it right.  They configure
  both the PCI and ISA buses, but it has been claimed that some older
  BIOSs can only do the PCI.  To try to find out more about your BIOS,
  look on the Web.  Please don't ask me as I don't have data on this.
  The details of the BIOS that you would like to know about may be hard
  to find (or not available).  Some BIOSs may have minimal PnP
  capabilities and try to turn over the difficult parts of the
  configuration task to Window utilities.  If this happens you'll either
  have to find another method (such as isapnptools) or try to set up the
  ESCD database if the BIOS has one.  See the next section.


  5.3.2.  The BIOS's ESCD Database

  The BIOS's maintains a non-volatile database containing a PnP-
  configuration that it will try to use.  It's called the ESCD (Extended
  System Configuration Data).  Again, the provision of ESCD is optional
  but most PnP-BIOSs have it.  The ESCD not only stores the resource-
  configuration of PnP devices but also stores configuration information
  of non-PnP devices (and marks them as such) so as to avoid conflicts.
  The ESCD data is usually saved on a chip and remains intact when the
  power is off, but sometimes it's kept on a hard-drive??

  The ESCD is intended to hold the last used configuration, but if you
  use a program such as Linux's isapnp or pci utilities (which doesn't
  update the ESCD) then the ESCD will not know about this and will not
  save this configuration in the ESCD.  A good PnP OS might update the
  ESCD so you can use it later on for a non-PnP OS (like standard
  Linux).  MS Windows does this only in special cases.  See ``Using
  Windows to set ESCD''.

  To use what's set in ESCD be sure you've set "Not a PnP OS" or the
  like in the BIOS's CMOS.  Then each time the BIOS starts up (before
  the Linux OS is loaded) it should configure things this way.  If the
  BIOS detects a new PnP card which is not in the ESCD, then it must
  then allocate bus-resources to the card and update the ESCD.  It may
  even have to change the bus-resources assigned to existing PnP cards
  and modify ESCD accordingly.

  If each device saved its last configuration in its hardware, hardware
  configuring wouldn't be needed each time you start your PC.  But it
  doesn't work this way.  So all the ESCD data needs to be kept correct
  if you use the BIOS for PnP.  There are some BIOSs that don't have an
  ESCD but do have some non-volatile memory to store info on which bus-
  resources have been reserved for use by non-PnP cards.  Many BIOSs
  have both.

  5.3.3.  Using Windows to set the ESCD

  If the BIOS doesn't set up the ESCD the way you want it (or the way it
  should be) then it would be nice to have a Linux utility to set the
  ESCD.  As of early 1999 there isn't any.  Thus one may resort to
  attempting to use Windows (if you have it on the same PC) to do this.

  There are three ways to use Windows to try to set/modify the ESCD.
  One way is to use the ICU utility designed for DOS or Windows 3.x.  It
  should also work OK for Windows 9x/2k ??  Another way is to set up
  devices manually ("forced") under Windows 9x/2k so that Windows will
  put this info into the ESCD when Windows is shut down normally.  The
  third way is only for legacy devices that are not plug-and-play.  If
  Windows knows about them and what bus-resources they use, then Windows
  should put this info into the ESCD.

  If PnP devices are configured automatically by Windows without the
  user "forcing" it to change settings, then such setting will probably
  not make it into the ESCD.  Of course Windows may well decide on its
  own to configure the same as what is set in the ESCD so they could
  wind up being the same by coincidence.

  Windows 9x are PnP operating systems and automatically PnP-configure
  devices.  They maintain their own PnP-database deep down in the
  Registry (stored in binary Windows files).  There is also a lot of
  other configuration stuff in the Registry besides PnP-bus-resources.
  There is both a current PnP resource configuration in memory and
  another (perhaps about the same) stored on the hard disk.  To look at
  (the one in memory?) this indirectly in Windows98 or to force changes
  you use the Device Manager.

  In Windows98 There are 2 ways to get to the Device Manager: 1. My
  Computer --> Control Panel --> System Properties --> Device Manager.
  2. (right-click) My Computer --> Properties --> Device Manager.  Then
  in Device Manager you select a device (sometimes a multi-step process
  if there are a few devices of the same class).  Then click on
  Properties and then on Resources.  To attempt to change the resource
  configuration manually, uncheck "Use automatic settings" and then
  click on  "Change Settings".  Now try to change the setting, but it
  may not let you change it.  If it does let you, you have "forced" a
  change.  A message should inform you that it's being forced.  If you
  want to keep the existing setting shown by Windows but make it
  "forced" then you will have to force a change to something else and
  then force it back to its original setting.

  To see what has been "forced" under Windows98 look at the "forced
  hardware" list: Start --> Programs --> Accessories --> System Tools
  --> System Information --> Hardware Resources --> Forced Hardware.
  When you "force" a change of bus-resources in Windows, it should put
  your change into the ESCD (provided you exit Windows normally).  >From
  the "System Information" window you may also inspect how IRQs and IO
  ports have been allocated under Windows.

  Even if Windows shows no conflict of bus-resources, there may be a
  conflict under Linux.  That's because Windows may assign bus-resources
  differently than the ESCD does.  In the the rare case where all
  devices under Windows are either legacy devices or have been "forced",
  then Windows and the ESCD configurations should be identical.


  5.3.4.  Adding a New Device (under Linux or Windows)

  If you add a new PnP device and have the BIOS set to "not a PnP OS",
  then the BIOS should automatically configure it and store the
  configuration in ESCD.  If it's a non-PnP legacy device (or one made
  that way by jumpers, etc.) then there are a few options to handle it.
  You may be able to tell the BIOS directly (via the CMOS setup menus)
  that certain bus-resources it uses (such as IRQs) are reserved and are
  not to be allocated by PnP.  This does not put this info into the
  ESCD.  But there may be a BIOS menu selection as to whether or not to
  have these CMOS choices override what may be in the ESCD in case of
  conflict.  Another method is to run ICU under DOS/Windows.  Still
  another is to install it manually under Windows 9x/2k and then make
  sure its configuration is "forced" (see the previous section).  If
  it's "forced" Windows should update the ESCD when you shut down the
  PC.


  5.4.  Isapnp (part of isapnptools)

  Unfortunately, much of the documentation for isapnp is still difficult
  to understand unless you know the basics of PnP.  This HOWTO should
  help you understand it as well the FAQ that comes with it.  isapnp is
  only for PnP devices on the ISA bus (non-PCI).  Running the Linux
  program "isapnp" at boot-time will configure such devices to the
  resource values specified in /etc/isapnp.conf.  Its possible to create
  this configuration file automatically but you then must edit it
  manually to chose between various options.  With isapnp, a device
  driver which is part of the kernel may run too early before isapnp has
  set the address, etc. in the hardware.  This results in the device
  driver not being able to find the device.  The driver trys the right
  address but the address hasn't been set yet in the hardware.

  If your Linux distribution automatically installed isapnptools, isapnp
  may already be running at startup.  In this case, all you need to do
  is to edit /etc/isapnp.conf per "man isapnp.conf".  Note that this is
  like manually configuring PnP since you make the decisions as to how
  to configure as you edit the configuration file.  You can use the
  program "pnpdump" to help create the configuration file.  It almost
  creates a configuration file for you but you must skillfully edit it a
  little before using it.  It contains some comments to help you edit
  it.  If you use "isapnp" for configuring and have a PnP BIOS, you
  should probably tell the BIOS (when you set it up) that you don't have
  a PnP OS since you may want the BIOS to configure the PCI devices.
  While the BIOS may also configure the ISA devices, isapnp will redo
  it.

  The terminology used in the /etc/isapnp.conf file may seem odd at
  first.  For example for an I0 address of 0x3e8 you might see "(IO 0
  (BASE 0x3e8))" instead.  The "IO 0" means this is the first (0th) IO
  address-range that this device uses.   Another way to express all this
  would be: IO[0] = 0x3e8" but isapnp doesn't do it this way.  IO 1"
  would mean that this is the second IO address range used by this
  device, etc.  "INT 0" has a similar meaning but for IRQs (interrupts).
  A single card may contain several physical devices and the above
  explanation was for just one of these devices.


  5.5.  PCI Utilities

  The new package PCI Utilities (= pciutils, incorrectly called
  "pcitools"), should let you manually PnP-configure the PCI bus.
  "lspci" lists bus-resources while "setpci" sets resource allocations
  in the hardware devices.


  5.6.  Patch the Kernel to Make Linux PnP

  David Howells has created a patch to do this called "Linux Kernel
  Configuration/Resource Manager" (sometimes called Hardware
  Configuration Manager).  In late 1999 the patch was not available at
  his website.  This may mean there is no patch available for recent
  versions of the kernel.

  For previous patches the resulting kernel was claimed to be stable but
  bugs have been reported.  The patch included documentation such as
  serial.txt to show how to deal with the serial port.  It provided
  "files" in the /proc tree so that you can see what is going on and can
  echo commands into one of these files for custom configuration.  One
  problem is that most device drivers don't know about it so that you
  still had to use the traditional configuration files, etc. for
  configuration.  The webpage for it is  <http://www.astarte.free-
  online.co.uk>


  5.7.  Windows Configures

  If you have Windows9x (or 2k) on the same PC, then just start Windows
  and let it configure PnP.  Then start Linux from Windows (or DOS).  It
  been reported that Windows erased the IRQs from PCI devices registers.
  Then Linux complained that it found a zero IRQ.  Thus you may not be
  able to use this method.


  5.8.  Device Driver Configures

  A few device drivers will use PnP methods to set the bus-resources in
  the hardware but only for the device that they control.  Since the
  driver has done the configuring, it obviously knows the configuration
  and there is no need for you to tell it this info.

  The problem with this is twofold.  It's difficult to incorporate all
  of this into the driver, and the driver may grab bus-resources that
  are needed by other devices.  It does make it easy for the user but a
  PnP Linux kernel might be better.  See ``Linux Needs to Cope Better
  with PnP''


  5.9.  PnP Software/Documents


  o  Isapnptools homepage <http://www.roestock.demon.co.uk/isapnptools/>

  o  Patch to  make the Linux kernel PnP <http://www.astarte.free-
     online.co.uk>

  o  PnP driver project <http://www.io.com/~cdb/mirrors/lpsg/pnp-
     linux.html>

  o  PnP Specs. from Microsoft
     <http://www.microsoft.com/hwdev/respec/pnpspecs.htm>

  o  Book: PCI System Architecture, 3rd ed. by Tom Shanley +, MindShare
     1995.  Covers PnP-like features on the PCI bus.

  o  Book: Plug and Play System Architecture, by Tom Shanley, Mind Share
     1995.  Details of PnP on the ISA bus.  Only a terse overview of PnP
     on the PCI bus.


  6.  Tell the Driver the Configuration

  6.1.  Introduction

  Just how this is done depends upon the driver.  Some drivers have more
  than one way to find out how their physical device is configured.  At
  one extreme is the case where you must hard-code the bus-resources
  into the kernel and recompile.  At the other extreme, the driver does
  everything automatically and you have nothing to do.  It may even set
  the bus-resources in the hardware using PnP methods.

  In the middle are cases where you run a program to give the resource
  info to the driver or put the info in a file.  In some cases the
  driver may probe for the device at addresses where it suspects the
  device resides.  It may then try to test various IRQs to see which one
  works.   It may or may not automatically do this.  In other cases the
  driver may use PnP methods to find the device and how the bus-
  resources have been set, but will not actually set them.  It may also
  look in some of the files in the /proc directory.

  One may need to give the bus-resources as a parameter to the kernel to
  to a loadable module.  See /usr/lib/modules_help/descr.gz for a list
  of possible parameters.  The module to load is listed in /etc/modules
  along with its parameters.  In some other case the bus-resources may
  be given as parameters to the kernel.  These are put into the
  lilo.conf file as append="...".   Then the lilo program must be run to
  save this in the kernel boot code.

  While there is great non-uniformity about how drivers find out about
  bus-resources, the end goal is the same.  There are so many different
  hardware devices and drivers for them that you may need to look at
  documentation for your driver to find out how it finds out about bus-
  resources and what you need to do to insure that it gets the info it
  needs.  Some brief info on a few drivers is presented in the following
  section.


  6.2.  Serial Port Driver: setserial

  For the standard serial port driver (not for multiport cards) you use
  setserial to configure the driver.  It is often run from a start-up
  file.  In newer versions there is a /etc/serial.conf file that you
  "edit" by simply using the setserial command in the normal way and
  what you set using setserial is saved in the serial.conf configuration
  file.  The serial.conf file should be consulted when the setserial
  command runs from a start-up file.  Your distribution may or may not
  set this up for you.

  There are two different ways to use setserial depending on the options
  you give it.  One way is used to manually tell the driver the
  configuration.  The other way is to probe at a given address and
  report if a serial port exists there.  It can also probe this address
  and try to detect what IRQ is used for this port.  The driver runs
  something like setserial at start-up but it doesn't probe for IRQs, it
  just assigns the "standard" IRQ which may be wrong.  It does probe for
  the existence of a port.  See Serial-HOWTO for more details.


  6.3.  Sound Card Drivers

  6.3.1.  OSS-Lite

  You must give the IO, IRQ, and DMA as parameters to a module or
  compile them into the kernel.  But some PCI cards will get
  automatically detected (likely by using the lspci command or the
  like).  RedHat supplies a program "sndconfig" which detects ISA PnP
  cards and automatically sets up the modules for loading with the
  detected bus-resources.


  6.3.2.  OSS (Open Sound System) and ALSA

  These will detect the card by PnP methods and then select the
  appropriate driver and load it.  It will also set the bus-resources on
  an ISA-PnP card.  You may need to manually intervene to avoid
  conflicts.  For the ALSA driver, support for ISA-PnP is optional and
  you may use isapnp tools if you want to.


  7.  What Is My Current Configuration?

  Here "configuration" means the assignment of PnP bus-resources
  (addresses, IRQs, and DMAs).  There are two parts to this question for
  each device.  Each part should have the same answer.

  1. What is the configuration of the device driver software?  I.e.:
     What does the driver think the hardware configuration is?

  2. What configuration (if any) is set in the device hardware?

  Of course the configuration of the device hardware and its driver
  should be the same (and it normally is).  But if things are not
  working right, there may be a difference.  This means the the driver
  has incorrect information about the actually configuration of the
  hardware.  This spells trouble.  If the software you use doesn't
  adequately tell you what's wrong (or automatically configure it
  correctly) then you need to investigate how your hardware devices and
  their drivers are configured.  While Linux device drivers should "tell
  all" in some cases it's not easy to determine what has been set in the
  hardware.

  Another problem is that when you view configuration messages on the
  screen, it's sometimes not clear whether the reported configuration is
  that of the device driver, the device hardware, or both.  If the
  device driver is assigned a configuration and then checks the hardware
  out to see if it's configured the same, then the configuration
  reported by the driver should be that of both the hardware and the
  driver.

  But some drivers don't do this may accept a configuration that doesn't
  check out.  For example, "setserial" will accept a configuration that
  doesn't check out (even if you've told it to probe for bus-resources).
  Thus "setserial" may only be telling you the configuration of the
  driver and not the hardware.

  Some info on configuration may be obtained by reading the messages
  from the BIOS and Linux that appear on the screen when you first start
  the computer.  These messages often flash by too fast to read but once
  they stop type Shift-PageUp a few times to scroll back to them.  To
  scroll forward thru them type Shift-PageDown.  Typing "dmesg" at any
  time to the shell prompt will show only the Linux kernel messages and
  miss some of the most important ones (including ones from the BIOS).
  The messages from Linux may sometimes only show what the device driver
  thinks the configuration is, perhaps as told it via an incorrect
  configuration file.

  The BIOS messages will show the actual hardware configuration at that
  time, but a PnP OS, isapnp, or pci utilities, may change it later.
  The BIOS messages are displayed first before the ones from Linux.  As
  an alternative to eventually using Shift-PageUp to read them, try
  freezing them by hitting the "Pause" key.  Press any key to resume.
  But once the messages from Linux start to appear, it's too late to use
  "Pause" since it will not freeze the messages from Linux.


  7.1.  How Are My Device Drivers Configured?

  There may be a programs you can run from the command line (such as
  "setserial" for serial ports) to determine this.   The /proc directory
  tree is useful.  /proc/ioports shows the I/O addresses that the
  drivers use (or try if it's wrong).  They might not be set this way in
  hardware.

  /proc/interrupts shows only interrupts currently in use and many that
  have been allocated to drivers don't show at all since they're not
  currently being used.  For example, even though your floppy drive has
  a floppy disk in it and is ready to use, the interrupt for it will not
  show unless its in use.  Again, just because an interrupt shows up
  here doesn't mean that it exists in the hardware.  A clue that it
  doesn't exist in hardware will be if it shows that 0 interrupts have
  been issued by this interrupt.  Even if it shows some interrupts have
  been issued, it may mean that this interrupt doesn't exist on that
  device does exist on some other device which is not in use, but which
  somehow has issued an interrupt or two.  As of kernel 2.2 the /proc
  tree has changed.


  7.2.  How Are My Hardware Devices Configured?

  It's easy to find out what bus-resources have been assigned to devices
  on the PCI bus with the "lspci" command.  For for kernels <: 2.2:
  /proc/pci will provide some info but it's not too easy to decipher.
  For the ISA bus you may try running pnpdump --dumpregs but it's not a
  sure thing.  The results may be difficult to decipher.  Don't confuse
  the read-port address which pnpdump "trys" (and finds something there)
  with the I/O address of the found device.  They are not the same.

  Messages from the BIOS at boot-time tell you how the hardware
  configuration was then.  If you rely on the BIOS for configuring, then
  it should still be the same.  Messages from Linux may be from drivers
  that have checked to see that the hardware is there (and possibly
  checked the IRQ and DMA).  Of course, if the device works fine, then
  it's likely configured the same as the driver.


  8.  Appendix

  8.1.  Addresses

  There are three types of addresses: main memory addresses, I/O
  addresses and configuration addresses.  On the PCI bus, configuration
  addresses constitute a separate address space just like I/O addresses
  do.  Except for the complicated case of ISA configuration addresses,
  whether or not an address on the bus is a memory address, I/O address,
  or configuration address depends only on the voltage on other wires
  (traces) of the bus.


  8.1.1.  ISA Bus Configuration Address (Read-Port etc.)

  For the ISA bus, there is technically no configuration address space,
  but there is a special way for the CPU to access PnP configuration
  registers on the PnP cards.  For this purpose 3 @ I/O addresses are
  allocated.  This is not 3 addresses for each card but 3 addresses
  shared by all cards.

  These 3 addresses are named read-port, write-port, and address-port.
  Each port is just one byte in size.  Each PnP card has many
  configuration registers so that just 3 addresses are not even
  sufficient for these registers on a single card.  To communicate with
  a certain card, a specially-assigned card number (handle) is sent to
  all cards at the write-port address.  After that only that the only
  card still listening is the card with this handle.  Then the address
  of the configuration register (of that card) is sent to the address-
  port (of all cards --but only one is listening).  Next communication
  takes place with one configuration register on that card by either
  doing a read on the read-port or a write on the write-port.

  The write-port is always at A79 and the address-port is always at 279
  (hex).  But the read-port is not fixed but is set by the configuration
  software at some address that will supposedly not conflict with any
  other ISA card.  If there is a conflict, it will change the address.
  All PnP cards get "programmed" with this address.  Thus if you use say
  isapnp to set or check configuration data it must determine this read-
  port address.


  8.1.2.  Address ranges

  The term "address" is sometimes used in this document to mean a
  contiguous range of addresses.  Since addresses are given in bytes, a
  single address only contains one byte but I/O (and main memory)
  addresses need more than this.  So a range of say 8 bytes is often
  used for I/O address while the range for main memory addresses
  allocated to a device is much larger.  For a serial port (an I/O
  device) it's sufficient to give the starting I/O address of the device
  (such as 3F8) since it's well known that the range of addresses for
  serial port is only 8 bytes.  The starting address is known as the
  "base address".


  8.1.3.  Address space

  For ISA, to access both I/O and (main) memory address "spaces" the
  same address bus is used (the wires used for the address are shared).
  How does the device know whether or not an address which appears on
  the address bus is a memory address or I/O address?  Well, there are 4
  dedicated wires on the bus that convey this information and more.  If
  a certain one of these 4 wires is asserted, it says that the CPU wants
  to read from an I/O address, and the main memory ignores the address
  on the bus.  The other 3 wires serve similar purposes.  In summary:
  Read and write wires exist for both main memory and I/O addresses (4
  wires in all).

  For the PCI bus it's the same basic idea also using 4 wires but it's
  done a little differently.  Instead of only one or the four wires
  being asserted, a binary number is put on the wires (16 different
  possibilities).  Thus more info may be conveyed.   Four of these 16
  numbers serve the I/O and memory spaces as in the above paragraph.  In
  addition there is also configuration address space which uses up two
  more numbers.  Ten extra numbers are left over for other purposes.


  8.1.4.  Range Check (ISA Testing for IO Address Conflicts)

  On the ISA bus, there's a method built into each PnP card for checking
  that there are no other cards that use the same address.  If two or
  more cards use the same IO address, neither card is likely to work
  right (if at all).  Good PnP software should assign bus-resources so
  as to avoid this conflict, but even in this case a legacy card might
  be lurking somewhere with the same address.

  The test works by a card putting a test number it's own IO registers.
  Then the PnP software reads it and verifies that it reads the same
  test number.  If not, something is wrong (such as another card with
  the same address.  It repeats the same test with another test number.
  Since it actually checks the range of IO addresses assigned to the
  card, it's called a "range check".  It could be better called an
  address-conflict test.  If there is an address conflict you get an
  error message and need to resolve it yourself.


  8.1.5.  Communicating Directly via Memory

  Traditionally, most I/O devices used only I/O memory to communicate
  with the CPU.  For example, the serial port does this.  The device
  driver, running on the CPU would read and write data to/from the I/O
  address space and main memory.  A faster way would be for the device
  itself to put the data directly into main memory.  One way to do this
  is by using ``DMA Channels'' or bus mastering.  Another way is to
  allocate some space in main memory to the device.  This way the device
  reads and writes directly to main memory without having to bother with
  DMA or bus mastering.  Such a device may also use IO addresses.


  8.2.  Interrupts --Details

  Interrupts convey a lot of information but only indirectly.  The
  interrupt signal (a voltage on a wire) just tells a chip called the
  interrupt controller that a certain device needs attention.  The
  interrupt controller then signals the CPU.  The CPU find the driver
  for this device and runs a part of it known as an "interrupt service
  routine" (or "interrupt handler").  This "routine" tries to find out
  what has happened and then deals with the problem such a transferring
  bytes from (or to) the device.   This program (routine) can easily
  find out what has happened since the device has registers at addresses
  known to the the driver software (provided the IRQ number and the I/O
  address of the device has been set correctly).  These registers
  contain status information about the device .  The software reads the
  contents of these registers and by inspecting the contents, finds out
  what happened, and takes appropriate action..

  Thus each device driver needs to know what interrupt number (IRQ) to
  listen to.  On the PCI bus (and for the serial ports on the ISA bus
  starting with Kernel 2.2) it's possible for two (or more) devices to
  share the same IRQ number.  When such an interrupt is issued, the CPU
  runs all interrupt service routines for all devices using that
  interrupt.  The first thing the first service routine does is to check
  to see if an interrupt actually happened for its device.  If there was
  no interrupt (false alarm) it likely will exit and the next service
  routine starts, etc.


  8.3.  PCI Interrupts

  PCI interrupts are different but since they are normally mapped to
  IRQ's they behave in about the same way.  A major difference is that
  PCI interrupts may be shared.  For example IRQ5 may be shared between
  two PCI devices.  This sharing ability is automatic: you don't need
  special hardware or software.  There have been some reports of
  situations where such sharing didn't work, but it's likely due to a
  defect in the device driver software.  All device drivers for PCI
  devices are supposed to provide for interrupt sharing.  Note that you
  can't share the same interrupt between the PCI and ISA bus.  However,
  illegal sharing will work provided the devices which are in conflict
  are not in use at the same time.  "In use" here means that a program
  is running which "opened" the device in it's C programming code.

  You may need to know some of the details of the PCI interrupt system
  in order to set up the BIOS's CMOS or to set jumpers on old PCI cards.
  Each PCI card has 4 possible interrupts: INTA#, INTB#, INTC#, INTD#.
  Thus for a 7-slot system there could be 7 x 4 = 28  different
  interrupt lines.  But the specs permit a fewer number of interrupt
  lines.  This is not too restrictive since interrupts may be shared.
  Many PCI buses seem to be made with only 4 interrupt lines.  Call
  these lines (wires or traces) W, X, Y, Z.  Suppose we designate the B
  interrupt from slot 3 as interrupt 3B.  Then wire W could be used to
  share interrupts 1A, 2B, 3C, 4D, 5A, 6B, 7C.  This is done by
  physically connecting wire W to wires 1A, 2B, etc.  Likewise wire X
  could be connected to wires 1B, 2C, 3D, 4A, 5B, 6C, 7D.  Then on
  startup, the BIOS maps the X, W, Y, Z to IRQ's.  After that it writes
  the IRQ that each device is mapped to into a hardware register in each
  device.  Then and anything interrogating the device can find out what
  IRQ it uses.

  The above mentioned wires X, W, Y, Z  are labeled per PCI specs as
  INTA#, INTB#, INTC# and INTD#.  This official PCI notation is
  confusing since now INTA# has 2 possible meanings depending on whether
  we are talking about a slot or the PCI bus.  For example, if 3C is
  mapped to X then we say that INTC# of slot 3 is cabled to INTA# (X) of
  the PCI bus.  Confusing notation.

  There's another requirement also.  A PCI slot must use the lower
  interrupt letters first.  Thus if a slot only uses one interrupt, it
  must be INTA#.  If it uses 2 interrupts they must be INTA# and INTB#,
  etc.  A card in a slot may have up to 8 devices on it but there are
  only 4 PCI interrupts for it.  This is OK since interrupts may be
  shared so that each of the 8 devices (if they exist) can have an
  interrupt.  The PCI interrupt letter of a device is often fixed and
  hardwired into the device.

  The BIOS assigns IRQs (interrupts) so as to avoid conflicts with the
  IRQs it knows about on the ISA bus.  Sometimes in the CMOS BIOS menu
  one may assign IRQs to PCI cards (but it's not simple as explained
  above).  There's a situation where Windows zeroed out all the IRQ
  numbers in the PCI cards after the IRQ mappings had been set.  Then
  someone running Windows booted Linux from Windows with the result that
  Linux only found only incorrect IRQs of zero.

  You might reason that since the PCI is using IRQ's (ISA bus) it might
  be slow, etc.  Not really.  The ISA Interrupt Controller Chip(s) has a
  direct interrupt wire going to the CPU so it can get immediate
  attention.  While signals on the ISA address and data buses need to go
  thru the PCI bus to get to the CPU, the IRQ interrupt signals go there
  almost directly.


  8.4.  Isolation

  This is only for the ISA bus.  Isolation is a complex method of
  assigning a temporary handle (id number or Card Select Number = CSN)
  to each PnP device on the ISA bus.  Since there are more efficient
  (but more complex) ways to do this, some might claim that it's a
  simple method.  Only one write address is used for PnP writes to all
  PnP devices so that writing to this address goes to all PnP device
  that are listening.  This write address is used to send (assign) a
  unique handle to each PnP device.  To assign this handle requires that
  only one device be listening when the handle is sent (written) to this
  common address.  All PnP devices have a unique serial number which
  they use for the process of isolation.  Doing isolation is something
  like a game.  It's done using the equivalent of just one common bus
  wire connecting all PnP devices and the isolation program.

  For the first round of the "game" all PnP devices listen on this wire
  and send out simultaneously a sequence of bits to the wire.  The
  allowed bits are either a 1 (positive voltage) or an "open 0" of no
  voltage (open circuit or tri-state).  Each PnP device just starts to
  sequentially send out its serial number, bit-by-bit, starting with the
  high-order bit, on this wire.  If any device sends a 1, a 1 will be
  heard on the wire by all other devices.  If all devices send an "open
  0" nothing will be heard on the wire.  The object is to eliminate (by
  the end of this first round) all but highest serial number device.
  "Eliminate" means to cease to listen anymore to the write address that
  all devices still in the game are still listening to.  This is also
  called "dropping out".  (Note that all serial numbers are of the same
  length.)

  First consider only the high order bit of the serial number which is
  put on the wire first by all devices which have no handle yet.  If any
  PnP device sends out a 0 (open 0) but hears a 1, this means that some
  other PnP device has a higher serial number, so it temporarily drops
  out of this round and doesn't listen anymore until the round is
  finished (when a handle is assigned to the winner: the highest serial
  number).  Now the devices still in the game all have the same leading
  digit (a 1) so we may strip off this digit and consider only the
  resulting "stripped serial number" for future participation in this
  round.  Then go to the start of this paragraph and repeat until the
  entire serial number has been examined for each device (see below for
  the all-0 case).

  Thus it's clear that the highest serial number will not be eliminated
  from the game.  But what happens if the leading digits (of the
  possibly stripped serial numbers) are all 0?  In this case an "open 0"
  is sent on the line and all participants stay in the game.  If they
  all have a leading 0 then this is a tie and the 0's are stripped off
  just like the 1's were in the above paragraph.  The game then
  continues as the next digit (of the serial number) is sent out.

  At the end of the round (after the low-order bit of the serial number
  has been sent out by whatever participants remain) only one PnP device
  with the highest serial number remains.  It then gets assigned a
  handle and drops out of the game permanently.  Then all the dropouts
  from the last round (that don't have a handle yet) reenter the game
  and a new round begins with one less participant.  Eventually, all PnP
  devices are assigned handles.  It's easy to prove that this algorithm
  works.

  Once all handles are assigned, they are used to address each PnP
  device and send it a configuration as well as to read configuration
  info from the PnP device.  Note that these handles are only used for
  PnP configuration and are not used for normal communication with the
  PnP device.  When the computer starts up, all of the handles are lost
  so that a PnP BIOS usually does the isolation process again each time
  you start your PC.

  END OF Plug-and-Play-HOWTO
























