  Plug-and-Play-HOWTO
  David S.Lawyer
   <mailto:dave@lafn.org>
  v1.07, August 2003

  Help with understanding and dealing with the complex Plug-and-Play
  (PnP) issue.  How to get PnP to work on your PC (if it doesn't
  already).  It doesn't cover what's called "Universal Plug and Play"
  (UPnP).  See ``Universal Plug and Play (UPnP)''
  ______________________________________________________________________

  Table of Contents



  1. Introduction

     1.1 1. Copyright, Trademarks, Disclaimer, & Credits
        1.1.1 Copyright
        1.1.2 Disclaimer
        1.1.3 Trademarks.
        1.1.4 Credits
     1.2 Future Plans; You Can Help
     1.3 New Versions of this HOWTO
     1.4 New in Recent Versions
     1.5 General Introduction.  Do you need 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 Addresses
     2.4 I/O Addresses and Allocating Them
     2.5 Memory Ranges
     2.6 IRQs --Overview
     2.7 DMA Channels  (ISA bus only)
     2.8 "Resources" for both Device and Driver
     2.9 The Problem
     2.10 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 How Linux Does PnP

  4. Setting up a PnP BIOS

     4.1 Do you have a PnP operating system?
        4.1.1 Interoperability with Windows
        4.1.2 I have a PnP OS
        4.1.3 I don't have a PnP OS: Windows 2000 and XP
        4.1.4 I don't have a PnP OS: Windows 95/98:
     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 Device Driver Configures, Reserving Resources
     5.3 BIOS Configures
        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 ISA cards only: Disable PnP ?
     5.5 Isapnp (part of isapnptools)
     5.6 PCI Utilities
     5.7 Windows Configures
     5.8 PnP Software/Documents

  6. Tell the Driver the Configuration

     6.1 Introduction
     6.2 Serial Port Driver Example
     6.3 Some Sound Card Driver Examples
        6.3.1 OSS-Lite
        6.3.2 OSS (Open Sound System) and ALSA

  7. How Do I Find Devices and How Are They Configured?

     7.1 Finding and How-Configured Are Related
     7.2 Devices Have Two "Configurations"
     7.3 Finding Hardware
     7.4 Boot-time Messages
     7.5 The /proc Directory Tree
     7.6 PCI Bus Inspection
     7.7 ISA Bus Introduction
     7.8 ISA PnP cards
     7.9 Non-PnP Cards
     7.10 Non-PnP Cards with jumpers
     7.11 Neither PnP nor jumpers
     7.12 Use MS Windows

  8. Error Messages

     8.1 Unexpected Interrupt
     8.2 Plug and Play Configuration Error (Dell BIOS)

  9. Appendix

     9.1 Universal Plug and Play (UPnP)
     9.2 Address Details
        9.2.1 Address ranges
        9.2.2 Address space
        9.2.3 Range Check (ISA Testing for IO Address Conflicts)
        9.2.4 Communicating Directly via Memory
     9.3 ISA Bus Configuration Addresses (Read-Port etc.)
     9.4 Interrupts --Details
     9.5 PCI Interrupts
     9.6 ISA Isolation


  ______________________________________________________________________

  1.  Introduction

  1.1.  1. Copyright, Trademarks, Disclaimer, & Credits

  1.1.1.  Copyright

  Copyright (c) 1998-2003 by David S. Lawyer  <mailto:dave@lafn.org>

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


  1. If it's not a translation: Email a copy of your derivative work (in
     a format LDP accepts) to the author(s) and maintainer (could be the
     same person).  If you don't get a response then email the LDP
     (Linux Documentation Project): submit@en.tldp.org.

  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

  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.


  1.1.3.  Trademarks.

  Any brand names (starts with a capital letter such as MS Windows)
  should be assumed to be a trademark).  Such trademarks belong to their
  respective owners.



  1.1.4.  Credits


  ·  Daniel Scott proofread this in March 2000 and found many typos,
     etc.

  ·  Pete Barrett gave a workaround to prevent Windows from zeroing PCI
     IRQs.


  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 couple
  of months 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 the code used by various Linux drivers to implement
  Plug-and-Play.  Nor have I looked into the details of how the kernel
  deals with it.  Thus this HOWTO is still incomplete.  It needs to
  explain more about the PCI bus and about "hot swapping".   It likely
  has some inaccuracies (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 few months
  or so and will be available to browse and/or download at LDP mirror
  sites.  For a list of mirror sites see:
  <http://tldp.org/mirrors.html>.  Various formats are available.  If
  you only want to quickly check the date of the latest version look at:
  <http://tldp.org/HOWTO/Plug-and-Play-HOWTO.html>.  The version you are
  now reading is: v1.07, August 2003 .


  1.4.  New in Recent Versions

  For a full revision history going back to the first version see the
  source file (in linuxdoc format) at
  <http://www.ibiblio.org/pub/linux/docs/HOWTO/other-formats/sgml/Plug-
  and-Play-HOWTO.sgml.gz>.

  v1.07 August 2003: New M$ url, reserve resources for isa-pnp, lspci+,
  scanport may not find hdw, finding dev. and config.  v1.06 September
  2002: Revised about telling the BIOS if the OS is PnP
  v1.05 July 2002 typos: or => of, and => an, A Allocate => Allocate,
  programs => program; Dell PCs: "Plug and Play Configuration Error",
  clarity on telling BIOS if your OS is PnP, "Intro to PnP" had
  truncated sentence, routing IRQs on PCI clarified, Change of emphasis
  in entire doc: Linux is now a PnP OS (sort of), PCI has almost
  replaced ISA

  The version 1.0 (Nov. 2000) was long overdue and recognized that the
  kernel is doing more in helping device drivers set up PnP.  Kernel 2.4
  is significantly improved in this respect.  There's still a lot of
  improvement needed in both this HOWTO and the way that Linux does PnP.


  1.5.  General Introduction.  Do you need this HOWTO?

  Plug-and-play (PnP) is a system which automatically detects devices
  such as disks, sound cards, ethernet cards, modems, etc.  It also does
  some low-level configuring of them.  To be detected by PnP, the device
  must be designed for PnP.  Non-PnP devices (or PnP devices which have
  been correctly PnP-configured), can often be detected by non-PnP
  methods.  The modern PCI bus is inherently PnP while the old ISA bus
  originally wasn't PnP but had PnP support added to it later.  So often
  PnP is used to only mean PnP for the old ISA bus.  In this HOWTO, PnP
  means PnP for both the ISA and the PCI bus.

  As time goes by the Linux kernel is becoming better at supporting PnP.
  In the 20th century, one could say that Linux was not really a PnP OS.
  But it's becoming a PnP OS even thought it still doesn't have a fully
  centralized plug-and-play system.  It does provide programs that
  device drivers can call on to do their own plug-and-play.  The kernel
  also reads all configuration registers of all devices and maintains a
  table of them that device drivers can consult.  Many drivers take
  advantage of this and find your PnP devices OK.  The BIOS hardware of
  your PC likely may also do some plug-and-play work.  Thus if
  everything works OK PnP-wise, you can use your computer without
  needing to know anything about plug-and-play.  But if some devices
  which are supported by Linux don't work (because they're not
  discovered or configured correctly by PnP) then you may need to read
  some of this HOWTO.  You'll learn not only about PnP but also learn
  about how communication takes place inside the computer.

  If you're having problems with a device, watch the messages displayed
  at boot-time (go back thru them using Shift-PageUp).  Check to see
  that you have the right driver for a device, and that the driver is
  being found and used.  If the driver is a module, type "lsmod" (as the
  root user) to see it it's loaded (in use).  If it's not a module then
  it should be built into the kernel.  There should be a file somewhere
  that tells what drivers are built into the kernel: (such as:
  /boot/config-2.4-20 in Debian).  Sometimes a device name (such as
  /dev/eth0) doesn't get a driver assigned to it unless the assignment
  is found in the file: /etc/modules.conf:  For example, to assign the
  "tulip" driver to eth0 you add a line to this file: "alias eth0
  tulip".

  This HOWTO doesn't cover the problem of finding and installing device
  drivers.  Perhaps it should.  One problem is that a certain brand of a
  card (or other physical device) may not say what kind of chips are
  used in it.  The driver name is often the same as the chip name and
  not the brand name.  One way to start to check on a driver is to see
  if it is discussed in the kernel documentation, in another HOWTO, or
  on the Internet.  Warning: Such documentation may be out of date.

  In this document I mention so many things that can go wrong that one
  who believes in Murphy's Law (If something can go wrong it will) may
  become quite alarmed.  But for PnP for most people: If something can
  go wrong it usually doesn't.  Remember that sometimes problems which
  seem to be PnP related are actually due to defective hardware or to
  hardware that doesn't fully conform to PnP specs.

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

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

  If you don't understand this section, read the next section ``How a
  Computer Finds Devices (and  conversely)''


  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
  physical device and its driver.  In order to achieve this, PnP
  allocates the following "bus-resources" to both drivers and hardware:
  I/O addresses, memory regions, IRQs, DMA channels (ISA bus only).
  These 4 things are sometimes called "1st order resources" or just
  "resources".  If you don't understand what these 4 bus-resources are,
  read the following subsections of this HOWTO: I/O Addresses, IRQs, DMA
  Channels, Memory Regions.  An article in Linux Gazette regarding 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 "files" 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.  The /etc directory
  has many configuration files but most of them are not for PnP
  configuring.  So most of the configuring of hardware devices has
  nothing to do with PnP or bus-resources.  For, example the
  initializing of a modem by an "init string" or setting it's speed is
  not 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 used 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 RAM
  memory to store programs and data (for fast access).  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, the
  USB bus, 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".
  Furthermore, 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
  hda3 (third partition on hard drive a), ttyS1 (the second serial
  port), eth0 (the first ethernet card), etc.

  To make matters more complicated, the particular device driver
  selected, say for example eth0, may depend on the type of ethernet
  card you have.  Thus eth0 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.  If the driver is a
  module, some of these assignments might be found in /etc/modules.conf
  (called "alias") while others may reside in an internal kernel table.
  For example, if you have an ethernet card that uses the "tulip" chip
  put "alias eth0 tulip" into /etc/modules.conf so that when your
  computer asks for eth0 it finds the tulip driver.  Other device names
  may have a standard driver associated with them so the above isn't
  always required.

  To control a device, the CPU (under the control of the device driver)
  sends commands and data to, and reads status and data 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.

  This communication channel is actually a little more complex than
  described above.  An "address" is actually a range of addresses so
  that sometimes the word "range" is used instead of "address".  There
  could even be more that one range (with no overlapping) for a single
  device.  Also, 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.  Addresses

  PCs have 3 address spaces: I/O, main memory (IO memory), and
  configuration (except that the old ISA bus lacks a genuine
  "configuration" address space).  All of these 3 types of addresses
  share the same bus inside the PC.  But the presence or absence of
  voltage on certain dedicated wires on the PC's bus tells which "space"
  an address is in: I/O, main memory, (see ``Memory Ranges''),  or
  configuration.  See ``Address Details'' for more details.  Only two of
  these 3 address spaces are used for device I/O: I/0 and main memory.
  I/O stands for Input-Output.


  2.4.  I/O Addresses and Allocating Them

  Devices were originally located in I/O address space but today they
  may use space in main memory.  An I/0 address is sometimes just called
  "I/O", "IO", "i/o" or "io".  The terms "I/O port" or "I/O range" are
  also used.  Don't confuse these IO ports with "IO memory" located in
  main memory.  There are two main steps to allocate the I/O addresses
  (or some other bus-resources such as interrupts on the ISA bus):


  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

  Often, the device driver does both of these.  The two step process
  above is something like the two part problem of finding someone's
  house number on a street.  Someone must install a number on the front
  of the house so that it may be found and then you must obtain (and
  write down) this house number so that you can find the house.  In
  computers the device hardware must first get the address it will use
  set a special register and then the device driver must obtain this
  address.  Both of these must be done, either automatically by software
  or by entering the data manually into files.  Problems may occur when
  only one of them gets done (or is attempted).


  For manual PnP configuration 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 may 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 hardware doesn't have the address you told
  setserial (or doesn't have any address set in it) then you're in
  trouble.

  An obvious requirement is that before the device driver can use an
  address it must be first set in the physical device (such as a 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 few paragraphs regarding I/O addresses
  applies with equal force to most other bus-resources: ``Memory
  Ranges'', ``IRQs --Overview'' and ``DMA Channels''.  What these are
  will be explained in the next 3 sections.  The exception is that IRQs
  on the PCI bus are not set by a card register but are set by a special
  routing chip on the motherboard.


  2.5.  Memory Ranges

  Many devices are assigned address space in main memory.  It's
  sometimes called "shared memory" or "memory-mapped IO" or "IO memory".
  This memory is physically located in the device.  When discussing bus-
  resources it's often just called "memory", "mem", or "iomem".  In
  addition to using such "memory", such a device might also use
  conventional IO address space.  To see what mem is in use on your
  computer, look at /proc/iomem.  This "file" includes the memory range
  used by your ordinary RAM memory chips but this really not strictly a
  part of iomem.

  When you insert a card that uses iomem, you are in effect also
  inserting a memory module for main memory.  A high address is selected
  for it by PnP so that it doesn't conflict with main memory chips.
  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) just as IO address space is shared between the device
  and the CPU.  This shared memory serves as a means of data "transfer"
  between the device and main memory. It's IO but it's not done in IO
  space.  Both the card and the device driver need to know where it is.

  ROM is different.  It is likely a program (perhaps a device driver)
  which will be used with the device.  It could be initialization code
  so that a device driver is still required.  Hopefully, it will work
  with Linux and not just MS 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".


  2.6.  IRQs --Overview

  After reading this you may read ``Interrupts --Details'' for many 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 or just an "irq"
  for short.  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
  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 tell its driver to fetch these
  bytes at once and transfer them from the device's nearly full buffer
  into main memory.  Another example is to signal the driver that the
  device has finished sending out a bunch of bytes and is now waiting
  for some more bytes from the driver so it can send them too.

  How should the device rapidly signal its driver?  It may not be able
  to use the main data bus since it's likely already in use.  Instead it
  puts a voltage on a dedicated interrupt wire (part of the bus) which
  is often reserved for that device alone.  This voltage signal is
  called an Interrupt ReQuest (IRQ) or just an "interrupt" for short.
  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 the device sends help requests 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 on.

  Once the device driver gets the interrupt from the device it must find
  out why the interrupt was issued and take appropriate action to
  service the interrupt.  On the ISA bus each device usually needs its
  own unique IRQ number.  For the PCI bus and other special cases the
  sharing of IRQs is allowed and the IRQ assignment is determined by a
  programmable routing chip.  See ``Interrupts --Details'' for how this
  works.


  2.7.  DMA Channels (ISA bus only)

  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


  1. 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 resource 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-requests
  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 special register on the physical device.


  2.8.  "Resources" for both Device and Driver

  Thus device drivers must be "attached" in some way to the hardware
  they control.  This is done by allocating 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 configuration registers on its card (or in a chip on the
  motherboard).  For the case of jumpers, it's the location of the
  jumpers themselves that store the bus-resource configuration in the
  device hardware (on the card, etc.).  For the case of PnP, the
  configuration register data is usually lost when the PC is powered
  down (turned off) so that the bus-resource data must be supplied to
  each device anew each time the PC is powered on.


  2.9.  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 data (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 network cards, 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 the case of manual configuration.  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 other info to the device.  It's actually
  a little more than one-way since the driver may get information from
  the device by reading its registers.  But the device can't initiate
  any communication this way.  To initiate communication the device
  needs an IRQ so it can send interrupts to its driver.  This creates a
  two-way communication channel where both the driver and the physical
  device can initiate communication.


  2.10.  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.  In this
  case, PnP is used only to identify the modem (read it's model code
  number).  This could be important if the modem is a software modem
  (linmodem) and requires a special driver.  There is a special PnP
  specification for such external serial devices (something connected to
  the serial port).

  Linux doesn't support this yet ??  For a hardware modem, the ordinary
  serial driver will work OK so there's little need for using the
  special serial PnP to find a driver.  You still need to tell the
  communications program what port (such as /dev/ttyS1) the modem is on.
  With PnP you wouldn't need to even do this.  With the advent of
  software modems that have Linux drivers (linmodems), it would be nice
  to have the appropriate driver install itself automatically via 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 narrower sense it is just setting bus-
  resources in the hardware devices.  For the case of Linux, it is often
  just a driver giving a command to set the bus-resources in it's device
  or determining how the BIOS has set them.  "PnP" often means just PnP
  on the ISA bus so the message from isapnp: "No Plug and Play device
  found" just means that no ISA PnP devices were found.  The standard
  PCI specifications (which are not called "PnP") provide the equivalent
  of PnP 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 formerly set in hardware devices by jumpers or
  switches.  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 but at first it wasn't called PnP (and often still
  isn't called PnP).  While the PCI bus specifications don't use the
  term PnP, it supports in hardware what today is called PnP.


  3.2.  How It Works (simplified)

  Here's how PnP should work in theory.  The PnP configuration program
  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 then informs the device driver of
  what it's done (except the BIOS can't do this).  It's not always this
  simple as the card (or routing table for PCI) may specify that it can
  only use certain IRQ numbers 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.

  One way commonly used to allocate resources is to start with one
  device and allocate it bus-resources.  Then do the same for the next
  device, etc.  Then if finally all devices get allocated resources
  without conflicts, then all is OK.  But if allocating a needed
  resource would create a conflict, then it's necessary to go back and
  try to make some changes in previous allocations so as to obtain the
  needed bus-resource.  This is called rebalancing.  Linux doesn't do
  rebalancing but MS Windows does in some cases.  For Linux, all this is
  done by the BIOS and/or kernel and/or device drivers.  In Linux the
  device driver doesn't allocate any resources until the driver starts
  up, so one way to avoid conflicts is just not to start any device that
  might cause a conflict.

  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 later)
  and PnP BIOSs do this but standard Linux doesn't.  Windows9x (and
  later) 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'').

  While MS Windows (starting with Windows 95) is a PnP OS, Linux was not
  originally a PnP OS but has been gradually becoming a PnP OS.  PnP
  originally worked in Linux because a PnP BIOS would configure the bus-
  resources and the device drivers would find out (using programs
  supplied by the Linux kernel) what the BIOS has done.  Today, most
  drivers can issue commands to do their own bus-resource configuring
  and don't need to rely on the BIOS.  Unfortunately a driver might take
  a bus-resource which another device will need later on.  Some device
  drivers may store the last configuration they used in a configuration
  file and use it the next time the computer is powered on.

  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 device needs to be re-configured 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.  At present, Linux can't allocate with this
  sophistication (and MS Windows XP may not be able to do it either).


  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 always PnP-
  configure devices needed to load the operating system from the hard-
  drive.

  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
  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 inform their drivers
  of what it did).


  3.4.  Buses

  ISA is the old bus of the old IBM PCs while PCI is a newer and faster
  bus from Intel.  The PCI bus was designed for what is today called
  PnP.  This 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's on the PCI bus type lspci.  Or type scanpci but it's not as
  easy to read.  The -v option will show more detail.  And/or look at
  the "file" /proc/pci.  The boot-up messages on your display show
  devices which have been found on various buses (use shift-PageUp to
  back up thru them).  See ``Boot-time Messages''

  For the ISA bus there was 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 a physical device.  As a result, the way PnP was
  shoehorned onto the ISA bus is very complicated.  Whole books have
  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 ``ISA Isolation'' for the
  complex details.

  Eventually, the ISA bus should become extinct.  When this happens, PnP
  will be a little easier since it will be easier 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.


  3.5.  How Linux Does PnP

  Linux has had  serious problems dealing with PnP and still has a
  problem but it's not as severe as it once was.  It's debatable whether
  or not Linux is really a PnP operating system.  It seems to mainly
  rely on and device drivers and the PnP BIOS to configure bus-resources
  for devices.

  But the kernel provides help for the drivers in the form of programs
  they may call on that do PnP.  In many cases, the device driver, with
  the help of such programs, does all the needed configuring.  In some
  cases the BIOS may configure and then the device driver may find out
  how the BIOS has configured it.  The kernel provides the drivers with
  some functions (program code) that the drivers may use to find out if
  their device exists, how it's been configured, and functions to modify
  the configuration.  Kernel 2.2 could do this only for the PCI bus but
  Kernel 2.4 has this feature for both the ISA and PCI buses (provided
  that the PNP options have been selected when compiling the kernel).
  This by no means guarantees that all drivers will fully and correctly
  use these features.
  In addition, the kernel helps avoid resource conflicts by not allowing
  two devices to use the same bus-resources at the same time.
  Originally this was only for IRQs, and DMAs but now it's for address
  resources as well.  For PCI, it allocates address resources while
  booting.

  Prior to Kernel 2.4, the standalone program: isapnp was often run to
  configure and/or get info from PnP devices on the ISA bus.  isapnp is
  still needed for cases where the device driver is not fully PnP for
  the ISA bus..  There was at least one attempt to make Linux a true PnP
  operating system.  See  <http://www.astarte.free-online.co.uk>.  But
  it never was put into the kernel.

  To see what help the kernel may provide to device drivers see the
  directory /usr/.../.../Documentation where one of the ... contains the
  word "kernel-doc" or the like.  Use the "locate" command to find it.
  In this documentation directory see pci.txt ("How to Write Linux PCI
  Drivers") and the file: /usr/include/linux/pci.h.  Unless you are a
  driver guru and know C Programming, these files are written so tersely
  that they will not actually teach you how to write a driver.  But it
  will give you some idea of what PnP type functions are available for
  drivers to use.  For the ISA bus see isapnp.txt and possibly (for
  kernel 2.4) /usr/include/linux/isapnp.h.

  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 a number
  of things that a real PnP operating system could handle better:


  ·  Allocate bus-resources when they are in short supply

  ·  Deal with more than one driver for a physical device

  ·  Find a driver for a detected device (instead of making drivers do
     the searching)

  ·  Central allocation of bus-resources would ease the job of
     programmers of device drivers

  The "shortage of bus-resources" problem is becoming less of a problem
  for two reasons:  One reason is that the PCI bus is replacing the ISA
  bus.  Under PCI there is no shortage of IRQs since IRQs may be shared
  (even though sharing is less efficient).  Also, PCI doesn't use DMA
  resources (although it does the equivalent of DMA without needing such
  resources).

  The second reason is that more and more physical devices are using
  main memory addresses instead of IO address space.  On 32-bit PCs
  there is 4GB of main memory address space and much of this bus-
  resource is available for device IO (unless you have 4GB of main
  memory installed).  Compare this to the IO address space which is
  limited to 64KB.  So the memory space for device IO is not (yet ?) in
  short supply.


  4.  Setting up a PnP BIOS

  When the computer is first turned on, the BIOS runs before the
  operating system is loaded.  Modern BIOSs are PnP and can configure
  some or all of the PnP devices.  Old PCI BIOS will only configure for
  the PCI bus.  Here are some of the choices which may exist in your
  BIOS's CMOS menu:



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

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

  ·  ``Reset the configuration?''


  4.1.  Do you have a PnP operating system?

  In any case the PnP BIOS will PnP-configure the hard-drive, video
  card, and keyboard to make the system bootable.  If you said you had a
  PnP OS it will leave it up to the operating system (or device drivers)
  to finish the configuration job.  If you said no PnP OS then the BIOS
  should configure everything.  If you only run Linux on your PC, you
  should probably tell it that you don't have a PnP operating system.
  If you also run MS Windows on your PC and said it was a PnP OS when
  you installed Windows, then you might try saying that you have a PnP
  OS to keep Windows 95/98 happy (but it might cause problems for Linux.
  For Windows 2000 it's claimed that Windows worked OK even if you say
  you don't have a PnP OS.  In this case Windows 2000 will report
  finding new hardware (even though it already knew about the hardware
  but didn't know how the BIOS Pnp-configured it).

  If you say you have a PnP OS then you rely on the Linux device drivers
  and possibly the program isapnp to take care of the bus-resource
  configuring.  This often works OK but sometimes doesn't.  Doing it
  this way has sometimes actually fixed problems.  This could be because
  the BIOS didn't do it's job right but Linux did.

  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''.  Device
  drivers that do configuring may modify what the BIOS has done.  So
  will the isapnp or PCI Utilities programs.


  4.1.1.  Interoperability with Windows

  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?  In the 1990's
  Windows suggested a yes answer and since Linux wasn't much of a PnP OS
  your could say no for Linux.  Having different answers for Windows and
  Linux means that you would have to set up the BIOS's CMOS menu
  manually each time you want to switch OSs.  This is a lot of bother,
  so it's best to have the same answer to the question for both Linux
  and Windows.

  In the 21st century, Windows 2000 and XP both suggest that you say no,
  it's not a PnP OS.  But Linux has become more PnP-like so you may want
  to say yes.  The situation is now sort of reversed from what it was.
  If you have no idea what to say, you might as well just say no (it's
  not a PnP OS).  Then if you have problems you might change the no to a
  yes.  Both Windows 2000/XP and Linux have become more tolerant about
  this and in many cases everything will work fine regardless of how you
  answer.  But if you want the BIOS to configure for Linux (and
  Windows), you would say no.



  4.1.2.  I have a PnP OS

  If you say that you have a PnP OS, then Linux may work OK if all the
  drivers and isapnp (if you use it) are able to configure OK.  Perhaps
  updating of the Linux OS and/or drivers will help.  Windows 95 and 98
  should work OK too.  Windows 2000 and XP will probably work OK too,
  but they might not.


  4.1.3.  I don't have a PnP OS: Windows 2000 and XP

  See the next section for Window 9x.  If you have Windows 2000 or XP it
  should work out OK (even if you said it was a PnP-OS when you first
  installed Windows 2000).  When you change to "not a PnP-OS", Windows
  2000 (and XP ??) will automatically PnP-reconfigure it's devices and
  tell you that it's finding new hardware and installing new devices.
  What it really means is that it's finding hardware which is already
  configured by the BIOS whereas before it found hardware that wasn't
  configured by the BIOS.  Perhaps it considers the hardware to be "new"
  since Windows 2000 may be finding it at a different address/irq than
  it has recorded in its registry.


  4.1.4.  I don't have a PnP OS: Windows 95/98:

  Now you are fibbing to Windows9x.   Since one might expect Windows be
  more sophisticated at handling PnP than Linux, one would expect
  Windows9x to be able to cope with with hardware that has been fully
  configured by the BIOS.  But it can't (although Windows 2000/XP can).

  What Windows9x seems to do when it finds hardware that is already
  configured by the BIOS is to just leave it alone and not reconfigure
  it.  Now Windows9x keeps a record of the bus-resource configuration in
  its registry.  If the BIOS configuration is different, it should
  either correct what's in its registry to conform to what the BIOS has
  set or reconfigure everything per what's in the registry.  Bad news.
  It seems to do neither.

  So it seems that Windows9x may just tell its device drivers what has
  been stored in the Windows Registry but this info may be wrong.  The
  actual hardware configuration (done by the BIOS) is what was stored in
  the ESCD and may not be the same as the Registry.  This means trouble.
  So for Windows to work OK you need to get the Registry to contain the
  bus-resource configuration which the BIOS creates from the ESCD.

  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.

  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 though they are still
  there.  A workaround for this is to select "skip file" and continue.

  As a test I "removed" a NIC card which used a Novell compatible
  driver.  Upon rebooting, Windows reinstalled it with Microsoft
  Networking instead of Novell.  This meant that the Novell Client
  needed to be reinstalled --a lot of unnecessary work.  So it may be
  better to not fib to Windows95/98 but instead to get Linux to
  configure bus-resources.


  4.2.  How are bus-resources to be controlled?

  Unless you have old non-pnp ISA cards, just set this to "auto".  If
  set to manual, you manually reserve some IRQ's, etc. for use on
  "legacy" (non-pnp) ISA cards.  The BIOS may or may not otherwise know
  about such legacy cards.  The BIOS will only know about these 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?

  Don't try this unless...  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 ISA 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).
  The configuring of bus-resources is normally done by the various
  device drivers using pnp support provided by modules or built into the
  kernel.  If this doesn't work, there are 4 other methods listed below
  to cope with PnP (but some may not be feasible in your situation).  If
  the BIOS configures it, you hope that the driver can find out what the
  BIOS did, otherwise you may need to tell the driver this in a
  configuration file or the like.


  ·  ``Device Driver Configures''

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

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

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

  ·  ``PCI Utilities'' is for configuring the PCI bus but the device
     driver should handle it

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

  Any of the above will set the bus-resources in the hardware but only
  the first one tells the driver what has been done.  How the driver
  gets informed depends on the driver.  You may need to do something to
  inform it.  See ``Tell the Driver the Configuration''



  5.2.  Device Driver Configures, Reserving Resources

  Many device drivers (with the help of code provided by the kernel)
  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.  This is obviously the easiest way to do
  it since you don't have to do anything if the driver does it all.

  If you have old pre-pnp ISA hardware, the Linux Pnp software may not
  know about it and the bus-resources it requires.  So it might
  erroneously allocate the resources that this old hardware needs to
  some other device.  The result is a resource conflict but there's a
  way to try to avoid it.  You can reserve the resources that the old
  ISA card needs by giving arguments to the isa-pnp module or to the
  kernel (if the pnp is built into the kernel).  For example, to reserve
  irq 5 give this argument to the isa-pnp module (or to the kernel):
  isapnp_reserve_irq=5.  See BootPrompt-HOWTO.  Instead of ..._irq there
  are also _io, _dma, and _mem.  Is this clever enough to prevent a PCI
  device from using such reserved resources ??

  For PCI devices, most drivers will configure PnP but for ISA devices
  it's problematical.  This is because PCI has always been inherently
  PnP (called "PCI Configuration").  For ISA, the kernel provided no
  functions for PnP configuring until version 2.4.  So if you have a
  modern version of both the kernel and the driver then the driver is
  more likely to configure ISA PnP (bus-resources).  But if you have
  older versions (or if the driver maintainer failed to add PnP support
  to it) then the driver may not configure ISA PnP.

  Unfortunately, a driver may grab bus-resources that are needed by
  other devices (but not yet allocated to them by the kernel).  Thus a
  true PnP Linux kernel would be better where the kernel did the
  allocation after all requests were in.  See ``How Linux Does PnP''.


  5.3.  BIOS Configures

  5.3.1.  Intro to Using the BIOS to Configure PnP

  If you have a PnP BIOS, it can configure the hardware.  If the driver
  can't do it, the BIOS probably can.  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 drivers 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 may
  not use the same configuration as was in the ESCD.  In this case it
  should update the ESCD to reflect the new situation.

  Your BIOS needs to support such configuring and there have been cases
  where it doesn't do it correctly or completely.  The BIOS also needs
  to be told via the CMOS menu that it's not a PnP OS.  While many
  device drivers will be able to automatically detect what the BIOS has
  done, in some cases you may need to determine it (not always easy).
  See ``What Is My Current Configuration?''  A possible advantage to
  letting the BIOS do it is that it does its work before Linux starts so
  it all gets done early in the boot process.

  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 seemingly expect the operating system to do it right.
  If this happens you'll either have to find another method 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 maintains a non-volatile database containing a PnP-
  configuration that it will try to use (if you claim that it's not a
  PnP OS).  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 Windows9x 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
  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 the 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 regarding
  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 wasn't any and now in 2002 no one has
  told me about 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 settings probably will
  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
  this in Windows98 or to force changes to it 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 here 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.  ISA cards only: Disable PnP ?

  PCI devices are inherently PnP so it can't be disabled.  But a few ISA
  devices had options for disabling PnP by jumpers or by running a
  Windows program that comes with the device (jumperless configuration).
  If the device driver can't configure it, this will avoid the possibly
  complicated task of doing PnP configuring.   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).

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


  5.5.  Isapnp (part of isapnptools)

  The isapnp standalone program is only for PnP devices on the ISA bus
  (non-PCI).  It was much needed prior to the 2.4 kernels.  After the
  2.4 kernel, which provided functionality to allow drivers deal with
  ISA PnP, the isapnp standalone program is less significant.  But the
  isa-pnp module (or the equivalent built into the kernel) is now very
  significant.  This module is called on by various device drivers to do
  configure bus-resources.

  In some cases Linux distributions have been set up to run isapnp
  automatically at startup.  If you need to set it up yourself much of
  the documentation for isapnp is 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.  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 should edit it manually
  to choose between various options.

  With isapnp there's a danger that a device driver which is built into
  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 tries 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.

  If the configuration file is wrong or doesn't exist, 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.  While the BIOS may also configure the ISA devices (if you've told
  it that you don't have a PnP OS), 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 but the above
  explanation was for just one of these devices.


  5.6.  PCI Utilities

  The package PCI Utilities (= pciutils, sometimes called "pcitools"),
  should let you manually PnP-configure the PCI bus.  "lspci" or
  "scanpci" (Xwindows) lists bus-resources while "setpci" sets resource
  allocations in the hardware devices.  It appears that setpci is mainly
  intended for use in scripts and presently one needs to know the
  details of the PCI configuration registers in order to use it.  That's
  a topic not explained here nor in the manual page for setpci.

  People have used this to configure PCI devices where the driver failed
  to do it.  An example is found in my Modem-HOWTO and Serial-HOWTO in
  the subsection "PCI: Enabling a disabled port".  However, enabling a
  device is of no use unless you have a working driver for the device.


  5.7.  Windows Configures

  This method uses MS Windows to configure and should be used only if
  all else fails.  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).  But there may be a problem with IRQs for PCI
  devices.  As Windows shuts down to make way for Linux, it may erase
  (zero) the IRQ which is stored in one of the PCI device's
  configuration registers.  Linux will complain that it has found an IRQ
  of zero.

  The above is reported to happen if you start Linux using a shortcut
  (PIF file).  But a workaround is reported where you still use the
  shortcut PIF.  A shortcut is something like a symbolic link in Linux
  but it's more than that since it may be "configured".  To start Linux
  (from DOS you create a batch file (script) which starts Linux.  (The
  program that starts Linux is in the package called "loadlin").  Then
  create a PIF shortcut to that batch file and get to the "Properties"
  dialog box for the shortcut.  Select "Advanced" and then check "MS-DOS
  mode" to get it to start in genuine MS-DOS.

  Now here's the trick to prevent zeroing the PCI IRQs.  Chick "Specify
  a new MS-DOS configuration".  Then either accept the default
  configuration presented to you or click on "Configuration" to change
  it.  Now when you start Linux by clicking on the shortcut, new
  configuration files (Config.sys and Autoexec.bat) will be created per
  your new configuration.

  The old files are stored as "Config.wos and Autoexec.wos".  After you
  are done using Linux and shut down your PC then you'll need these
  files again so that you can run DOS the next time you start your PC.
  You need to ensure that the names get restored to *.sys and *.bat.
  When you leave Windows/DOS to enter Linux, Windows is expecting that
  when you are done using Linux you will return to Windows so that
  Windows can automatically restore these files to their original names.
  But this doesn't happen since when you exit Linux you shut down your
  PC and don't get back to Windows.  So how do you get these files
  renamed?  It's easy, just put commands into your "start-Linux" batch
  file to rename these files to their *.bat and *.sys names.  Put these
  renaming commands into your batch file just before the line that loads
  Linux.

  Also it's reported that you should click on the "General" tab (of the
  "Properties" dialog of your shortcut) and check "Read-only".
  Otherwise Windows may reset the "Advanced Settings" to "Use current
  MS-DOS configuration" and PCI IRQs get zeroed.  Thus Windows erases
  the IRQs when you use the current MS-DOS configuration but doesn't
  erase when you use a new configuration (which may actually configure
  things identical to the old configuration).  Windows does not seem to
  be very consistent.



  5.8.  PnP Software/Documents


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

  ·  Proposal for a Configuration Manager for Linux
     <http://www.astarte.free-online.co.uk> (Never got into kernel.)

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

  ·  PnP Specs. from Microsoft
     <http://www.microsoft.com/hwdev/tech/pnp/default.asp>

  ·  Book: PCI System Architecture, 4th ed. by Tom Shanley +, MindShare
     1999.  Covers PnP-like features on the PCI bus.

  ·  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.

  ·  Book: Programming Plug and Play, by James Kelsey, Sams 1995.
     Details of programming to communicate with a PnP BIOS.  Covers ISA,
     PCI, and PCMCIA buses.


  6.  Tell the Driver the Configuration

  6.1.  Introduction

  A modern driver for a device will find out the bus-resource
  configuration without you having to tell it anything.  It may even set
  the bus-resources in the hardware using PnP methods.  Some drivers
  have more than one way to find out how their physical device is
  configured.  In the worst case you must hard-code the bus-resources
  into the kernel (or a module) and recompile.

  In the middle are cases such as where you run a program to give the
  bus-resource info to the driver or put the info in a configuration
  file.  In some cases the driver may probe for the device at addresses
  where it suspects the device resides (but it will never find a PnP
  device if it hasn't been enabled by PnP methods).  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 by the
  BIOS, etc. but will not actually set them.  It may also look at some
  of the "files" in the /proc directory.

  One may need to "manually" tell a driver what bus-resources it should
  use.  You give such bus-resources as a parameter to the kernel or to a
  loadable module.  If the driver is built into the kernel, you pass the
  parameters to the kernel via the "boot-prompt".   See The Boot-Prompt-
  HOWTO which describes some of the bus-resource and other parameters.
  Once you know what parameters to give to the kernel, one may put them
  into a boot loader configuration file.  For example, put append="...".
  into the lilo.conf file and then use the lilo command to get this info
  into the lilo kernel loader.

  If the driver is loaded as a module, in many cases the module will
  find the bus-resources needed and then set them in the device.  In
  other cases (mostly for older PCs) you may need to give bus-resources
  as parameters to the module.  Parameters to a module (including ones
  that automatically load) may be specified in /etc/modules.conf.  There
  are usually tools used to modify this file which are distribution-
  dependent.  Comments in this file should help regarding how to modify
  it.  Also, any module your put in /etc/modules will get loaded along
  with its parameters.

  While there is great non-uniformity about how drivers find out about
  bus-resources, the end goal is the same.  If you're having problems
  with a driver you may need to look at the driver documentation (check
  the kernel documentation tree).  Some brief examples of a few drivers
  is presented in the following sections:


  6.2.  Serial Port Driver Example

  For PCI serial ports (and for newer 2.4 kernels for ISA), the serial
  driver detects the type of serial port and PnP configures it.
  Unfortunately, there may be some PCI serial ports that are not
  supported yet.

  For the standard ISA serial port with older versions of the kernel and
  serial driver (not for multiport cards) you use setserial to inform
  the driver.  Using setserial is also a must for non-pnp serial ports.
  Setserial 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.  Some Sound Card Driver Examples

  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.  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.  How Do I Find Devices and How Are They Configured?

  7.1.  Finding and How-Configured Are Related

  Once you find your hardware, the same program that found it usually
  tells you how it's configured.  So finding out how it's configured is
  usually the same procedure as finding the hardware.


  7.2.  Devices Have Two "Configurations"

  Here "configuration" means the assignment of PnP bus-resources
  (addresses, IRQs, and DMAs).  For each device, there are two parts to
  the configuration question:

  1. What does the driver think the hardware configuration is?

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

     Each part should have the same answer (the same configuration).

  The configuration of the device hardware and its driver should be the
  same (and usually is).  But if things are not working right, it could
  be because there's a difference.  This means the the driver has
  incorrect information about the actual 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 may not be 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 has either set the configuration in the hardware or has
  otherwise checked the hardware then the driver should have the correct
  information.

  But sometimes the driver has been provided incorrect resources by a
  script, by incorrect resource parameters given to a module, or perhaps
  just hasn't been told what the resources are and tries to use
  incorrect default resources.  For example, one can uses "setserial" to
  tell the serial port driver an incorrect resource configuration and
  the driver accepts it without question.  But the serial port doesn't
  work right (if at all).


  7.3.  Finding Hardware

  A common problem is that the software doesn't detect your device
  and/or determine the right driver for it.  For PnP devices, detecting
  them is easy via PnP software.  This means that since the PCI bus is
  inherently PnP, there are no hidden devices.  Even though PnP devices
  are easy to find by PnP methods, if the driver doesn't use PnP methods
  but uses the old method of probing for them at likely address, they
  may not be found.  This is because that until the resources are set in
  a PnP device (by the BIOS or Linux), the device may have no address at
  all so probing at likely address yields nothing.  For the old ISA bus,
  some of the devices may be non-PnP and thus the old probing methods
  may find them.  So many drivers still probe, in addition to using PnP
  methods.

  Ways to Find Hardware Devices (and their configurations): (follow link
  to more details)

  ·  Watch the ``Boot-time Messages'' on the screen

  ·  Look in ``The /proc Directory Tree''

  ·  PCI: ``PCI Bus Inspection''

  ·  ISA Bus: ``ISA Bus Introduction''

  ·  ISA Bus: ``PnP cards''

  ·  ISA Bus: For ``Non-PnP Cards''

  ·  ISA Bus: For ``Cards with jumpers'',

  ·  ISA Bus: If ``Neither PnP nor jumpers'',

  ·  ``Use MS Windows''


  7.4.  Boot-time Messages

  Some info on configuration may be obtained by reading the messages
  from the BIOS and from 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 may 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.  Checking log files in
  /var/log may also be useful.

  For the PCI bus, the notation: 00:1a:0 means the PCI bus 00 (the main
  PCI bus), PCI card (or chip) 1a, and function 0 (the first device) on
  the card or chip.  The 2nd device on card (or chip) 08 would be:
  00:08:1.

  The BIOS messages display first and will show the actual hardware
  configuration at that time, but isapnp, or pci utilities, or device
  drivers may change it later.  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.

  Messages from the BIOS at boot-time tell you how the hardware
  configuration was then.  For the case where only the BIOS does the
  configuring, then it should still be the same.  Messages from Linux
  may be from drivers that used kernel PnP functions to inspect and/or
  set bus-resources.  These should be correct, but beware of messages
  that only show what the driver was told from a configuration file.  It
  could be wrong.  Of course, if the device works fine, then it's likely
  configured the same as the driver.


  7.5.  The /proc Directory Tree

  The /proc directory tree is useful for finding configuration and
  devices.  It seems that there are many files buried deep in this tree
  that contain bus-resource info.  Only a couple of them will be
  mentioned here.  /proc/ioports shows the I/O addresses that the active
  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.  Many
  interrupts that have been allocated to drivers don't show here 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 a few interrupts have been issued there is no guarantee that
  they came from the device shown.  It could be that some other device
  which is not currently in use has issued them.  A device not in use
  (per the kernel) may still issue some interrupts for various reasons.


  7.6.  PCI Bus Inspection

  It's easy to find out what bus-resources have been assigned to devices
  on the PCI bus with the "lspci" and/or "scanpci" commands or look at
  /proc/pci.  The option -v will show more detail.  /proc/buspci/devices
  shows a cryptic display so you probably want to avoid it.  Note that
  IRQs for /proc/pci are in hexadecimal.

  In most cases, for PCI you will only see how the hardware is now
  configured and not what resources are required.  In some cases you
  only see the base addresses (the starting addresses of the range) but
  not the ending addresses.  If you see the entire range then you can
  determine how many bytes of address resources are needed.


  7.7.  ISA Bus Introduction

  For cards on the ISA bus, it's not as simple as for the PCI bus which
  is inherently PnP.  Newer ISA cards are PnP but older ones are not.
  Also, some cards that are PnP have had their PnP disabled by special
  software which runs only on MS.  The non PnP cards are configured by
  jumpers on the card or by MS software.


  7.8.  ISA PnP cards

  If it's a PnP card you may try running pnpdump --dumpregs but it's not
  a sure thing.  The results may be seem cryptic but they can be
  deciphered.  Don't confuse the read-port address which pnpdump uses
  for communication with PnP cards  with the I/O address of the found
  device.  They are not the same.


  7.9.  Non-PnP Cards

  In contrast to PnP cards, non-PnP cards always have their resources
  set in the hardware.  That is they always have an address and IRQ.
  Sometimes this can be found by probing done by the device driver or by
  other software that does probing.  For example "scanport" (Debian only
  ??) probes most IO port address and may find ISA devices.  But be
  warned that it might hang your PC.  Sometimes it will fail to find
  hardware that's actually there (since the hardware has the default
  0xff in it's registers).  Even if It finds the hardware it will not
  show the IRQ nor will it positively identify the hardware.

  So one way to try to find such hardware is to start a driver, which
  may probe for such hardware.  By looking at the boot-time messages,
  you might see a driver start and find the hardware.  Otherwise, you
  may need to find a driver and start it (for example, by having it load
  as a module).


  Finding the right driver may be difficult.  Sometimes there just isn't
  any driver since some devices aren't supported by Linux (yet ?).  To
  determine which driver you need, look at any documentation which might
  identify the card.  If this fails, look on the card itself, including
  important names/numbers on the chips.  But the identification of the
  driver module you need may not be anywhere on the card.  You could
  find the FCC id on the card and then search the Internet with the FCC
  id number to try to find more information about the card (or the chips
  on it).


  7.10.  Non-PnP Cards with jumpers

  If the card has jumpers to set the resources (configuration) then one
  may look at how the jumpers are set.  There are some cards that had
  both PnP and jumpers.   They worked like jumper cards if PnP was
  somehow disabled.  Sometimes a card has labels on it showing how the
  jumpers are set (or at least giving some clue).  You may need the
  documentation that came with the card (either printed or on a floppy
  disk).  Perhaps you can find it on the Internet.


  7.11.  Neither PnP nor jumpers

  One the most difficult cases is where software running under MS has
  been used to configure either a non-PnP card or a PnP card where PnP
  has been disabled by the same MS software.  So you can't configure it
  by PnP nor by jumpers.  In this case your only hope is to probe for
  addresses  as described in ``Non-PnP Cards''.


  7.12.  Use MS Windows

  Some people have attempted to use Windows to see how bus-resources
  have been set up.  Unfortunately, since PnP hardware forgets its bus-
  resource configuration when powered down, the configuration may not be
  the same under Linux.  For non PnP hardware (or where someone has
  disabled PnP inside the device by jumpers or Windows software), then
  using Windows should work OK.  Even for PnP, it often turns out to be
  the same because in many cases both Windows and Linux simply accept
  what the BIOS has set.  But where Windows and/or Linux do the
  configuring, they may do it differently.  So don't count on PnP
  devices being configured the same.


  8.  Error Messages

  8.1.  Unexpected Interrupt

  This means that an interrupt happened that no driver expected.  It's
  unlikely that the hardware issued an interrupt by mistake.  It's more
  likely that the software has a minor bug and doesn't realize that some
  software did something to cause the interrupt.  In many cases you can
  safely ignore this error message, especially if it only happens once
  or twice at boot-time.  For boot-time messages, look at the messages
  which are nearby for a clue as to what is going on.  For example, if
  probing is going on, perhaps a probe for a physical device caused that
  device to issue an interrupt that the driver didn't expect.  Perhaps
  the driver wasn't listening for the correct IRQ number.

  8.2.  Plug and Play Configuration Error (Dell BIOS)

  The BIOS was unable to configure bus-resource.  There may be an
  interrupt conflict which can't be avoided.  Dell suggests that you
  remove some of your non-essential cards and see if it goes away.  In
  one case this problem was due to a defective motherboard.
  9.  Appendix

  9.1.  Universal Plug and Play (UPnP)

  This is actually a sort of network plug-and-play developed by
  Microsoft but usable by Linux.  You plug something into a network and
  that something doesn't need to be configured provided it will only
  communicate with other UPnP enabled devices on the network.  Here
  "configure" is used in the broad sense and doesn't mean just
  configuring bus-resources.  One objective is to allow people who know
  little about networks or configuring to install routers, gateways,
  network printers, etc.  A major use for UPnP would be in wireless
  networking.

  UPnP uses:

  ·  Simple Service Discovery Protocol to find devices

  ·  General Event Notification Architecture

  ·  Simple Object Access Protocol for controlling devices

  This HOWTO doesn't cover UPnP.  UPnP for Linux is supported by Intel
  which has developed software for it.  There are other programs which
  do about the same thing as UPnP.  A comparison of some of them is at
  <http://www.cs.umbc.edu/~dchakr1/papers/mcommerce.html>


  9.2.  Address Details

  There are three types of addresses: main memory addresses, I/O
  addresses (ports) 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.  For the ISA
  configuration addresses see ``ISA Bus Configuration Addresses (Read-
  Port etc.)'' for details


  9.2.1.  Address ranges

  The term "address" is sometimes used in this document to mean a
  contiguous range of addresses.  Since addresses are in units of bytes,
  a single address is only the location of a single 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".  Sometimes just the word "range" is used to mean
  "address range".


  9.2.2.  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.  Thus 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 of 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.


  9.2.3.  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 I/O 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 known test number in its 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.


  9.2.4.  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.


  9.3.  ISA Bus Configuration Addresses (Read-Port etc.)

  These addresses are also known as the "Auto-configuration Ports".  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 and each addresses only a single byte (there is no "range").
  This is not 3 addresses for each card but 3 addresses shared by all
  ISA-PnP 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 the configuration registers on a single card.  To solve
  this problem, each card is assigned a card number (handle) using a
  technique called "isolation".  See ``ISA Isolation'' for the complex
  details.

  Then to configure a certain card, its card number (handle) is sent out
  via the write-port address to tell that card that it is to listen at
  its address port.  All other cards note that this isn't their card
  number and thus don't listen.  Then the address of a configuration
  register (for that card) is sent to the address-port (for all cards
  --but only one is listening).  Next, data transfer takes place with
  that 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).  The read-port is not fixed but is set by the configuration
  software at some address (in the range 203-3FF) that will hopefully
  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.


  9.4.  Interrupts --Details

  Interrupts convey a lot of information but only indirectly.  The
  interrupt request 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 then
  interrupts whatever it was doing, finds 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.  For example, bytes may need
  to be transferred from/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 some special cases on the ISA bus)
  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 its device registers to see if
  an interrupt actually happened for its device.  If it finds that its
  device didn't issue an interrupt (a false alarm) it likely will
  immediately exit and the service routine begins for the second device
  using that same interrupt, etc, etc.

  The putting of a voltage on the IRQ line is only a request that the
  CPU be interrupted so it can run a device driver.  In almost all cases
  the CPU is interrupted per the request.  But interrupts may be
  temporarily disabled or prioritized so that in rare cases the actual
  interrupt doesn't happen (or gets delayed).  Thus what was above
  called an "interrupt" is more precisely only an interrupt request and
  explains why IRQ stands for Interrupt ReQuest.


  9.5.  PCI Interrupts

  There are two newer developments in PCI interrupts that are not
  covered here.  They are especially important for cases of more than
  one CPU per computer.  One is the Advanced Programmable Interrupt
  Controller (APIC).  See the file "IO-APIC" in the i386 directory of
  the kernel documentation.  Another new development is Message
  Signalled Interrupts (MSI) where the interrupt is just a message sent
  to a special address over the main computer bus (no interrupt lines
  needed).  But the device that sends such a message must first gain
  control of the main bus so that it can send the interrupt message.
  Such a message contains more info than just "I'm sending an
  interrupt".

  Ordinary PCI interrupts are different than ISA interrupts, but since
  they are normally mapped to IRQs they behave in about the same way.
  One major difference is that the BIOS does this mapping.  Under Linux
  it's not feasible to change it ?? unless the CMOS menu will let you do
  it.  But if you have the advanced APIC then there's a way to specify
  it.

  Another major difference is that PCI interrupts may be shared.  For
  example IRQ5 may be shared between two PCI devices.  This sharing
  ability is built into the hardware and all device drivers are supposed
  to support it.  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
  its C programming code.

  Here are some of the details of the PCI interrupt system.  Each PCI
  card (and device mounted on the motherboard) has 4 possible
  interrupts: INTA#, INTB#, INTC#, INTD#.  From now on we will call them
  just A, B, C, and D.  Each has its own pin on the edge connector of a
  PCI card.  Thus for a 7-slot system (for 7 cards) there could be 7 x 4
  = 28  different interrupt lines for the cards.  But the specs permit a
  fewer number of interrupt lines, so many PCI buses seem to be made
  with only 4 interrupt lines.  This is not too restrictive since
  interrupts may be shared.  Call these lines (wires or traces) W, X, Y,
  Z.  There is an "interrupt router" chip that routes W, X, Y, Z to
  selected IRQs.  This routing can be changed by the BIOS or software.
  For example, W may be routed to IRQ5.  Suppose we designate the B
  interrupt from slot 3 as interrupt 3B.  Then interrupt 3B could be
  permanently connected to W which is routed to IRQ5.

  One simple method of connecting (hard-wiring) these lines from PCI
  devices (such as 3B) to the interrupts W, etc. would be to connect all
  A interrupts (INTA#) to line W, all B's to X, etc.  This method was
  once used many years ago but it is not a good solution.  Here's why.
  If a card only needs one interrupt, it's required that it use A.  If
  it needs two interrupts, it must use both A and B, etc.  Thus INTA# is
  used much more often than INTD#.  So one winds up with an excessive
  number of interrupts sharing the first line (W connected to all the
  INTA#).  To overcome this problem one may connect them in a more
  complicated way so that each of the 4 interrupt lines (W, X, Y, Z)
  will share about the same number of actual PCI interrupts.

  One method of doing this would be to have wire W 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, etc.  Then on startup, the BIOS maps the X, W,
  Y, Z to IRQs.  After that it writes the IRQ that each device uses into
  a hardware configuration register in each device.  From then on, any
  program interrogating this register can find out what IRQ the device
  uses.  Note that writing the IRQ in a register on a PCI card doesn't
  in any way set the IRQ for that device.

  A card in a slot may have up to 8 devices on it but there are only 4
  PCI interrupts for it (A, B, C, D).  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 assignment of interrupts is done by
  the BIOS mapping the PCI interrupts to the ISA interrupts as mentioned
  above.  If there are only 4 lines (W, X, Y, and Z) as in the above
  example, the mapping choices that the PCI BIOS has are limited.  Some
  motherboards may use more lines and thus have more choices.  The BIOS
  knows about how this is wired.

  On the PCI bus, the BIOS assigns IRQs (interrupts) so as to avoid
  conflicts with the IRQs it knows about on the ISA bus.  Sometimes the
  CMOS BIOS menu may allow one to assign IRQs to PCI cards or to tell
  the BIOS what IRQs are to be reserved for ISA devices.  Also, a PnP
  operating system (for example MS Windows) could attempt to assign IRQs
  after first finding out what the BIOS has done.  The assignments are
  known as a "routing table".  If MS Windows makes such IRQ assignment
  dynamically (such as a docking event) it's called "IRQ steering".
  The BIOS may support it's own IRQ steering (which Linux could use).
  Thus if Windows 9x changes what the BIOS set and you use Linux after
  Windows without turning off your PC, the IRQs may be different.
  Windows 2000 and XP doesn't change what the BIOS has set, but it may
  add a new device (with a new IRQ).

  You might think that since the PCI is using IRQs (designed for the ISA
  bus) it might be slow since the ISA bus is slow.  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 may be slow to get to the CPU, the IRQ
  interrupt signals get there almost instantly.


  9.6.  ISA 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 to 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).  To do this, each PnP device just
  starts to sequentially send out its serial number on this wire,
  voltage (open circuit or tri-state).  To do this, each PnP device just
  starts to sequentially send out its serial number on this wire, bit-
  by-bit, starting with the high-order bit.  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 drop out of this round of the
  game and thus temporarily cease to listen anymore to the wire.  (Note
  that all serial numbers are of the same length.)  When there remains
  only one device still listening, it will be given a handle (card
  number).

  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.  Now the devices remaining in the game (for this
  round) 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 only cards with the lower serial number get
  eliminated during a round.  But what happens if all devices in the
  game all send out a 0 as their high-order bit?  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) only one PnP device with the highest serial number
  remains in the game.  It then gets assigned a handle and drops out of
  the game permanently.  Then all the dropouts from the previous 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.  The actual
  algorithm is a little more complex than that presented above since
  each step is repeated twice to ensure reliability and the repeats are
  done somewhat differently (but use the same basic idea).

  Once all handles are assigned, they are used to address each PnP
  device for sending/reading configuration data.  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
  a PnP BIOS will often do such an isolation and then a PnP
  configuration.  After that, all the handles are "lost" so that if one
  wants to change (or inspect) the configuration again, the isolation
  must be done over again.

  END OF Plug-and-Play-HOWTO



