Plug and Play BIOS Specification Compaq Computer Corporation Phoenix Technologies Ltd. Intel Corporation

Plug and Play BIOS Specification Compaq Computer Corporation Phoenix Technologies Ltd. Intel Corporation
Compaq Computer Corporation
Phoenix Technologies Ltd.
Intel Corporation
Plug and Play BIOS Specification
Version 1.0A
May 5, 1994
This specification has been made available to the public. You are hereby granted the right to use,
implement, reproduce, and distribute this specification with the foregoing rights at no charge. This
specification is, and shall remain, the property of Compaq Computer Corporation ("Compaq") Phoenix
Technologies LTD ("Phoenix") and Intel corporation ("Intel").
NEITHER COMPAQ, PHOENIX NOR INTEL MAKE ANY REPRESENTATION OR
WARRANTY REGARDING THIS SPECIFICATION OR ANY PRODUCT OR ITEM
DEVELOPED BASED ON THIS SPECIFICATION. USE OF THIS SPECIFICATION FOR ANY
PURPOSE IS AT THE RISK OF THE PERSON OR ENTITY USING IT. COMPAQ, PHOENIX
AND INTEL DISCLAIM ALL EXPRESS AND IMPLIED WARRANTIES, INCLUDING BUT
NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE AND FREEDOM FROM INFRINGEMENT. WITHOUT LIMITING
THE GENERALITY OF THE FOREGOING, NEITHER COMPAQ, PHOENIX NOR INTEL
MAKE ANY WARRANTY OF ANY KIND THAT ANY ITEM DEVELOPED BASED ON THIS
SPECIFICATION, OR ANY PORTION OF IT, WILL NOT INFRINGE ANY COPYRIGHT,
PATENT, TRADE SECRET OR OTHER INTELLECTUAL PROPERTY RIGHT OF ANY
PERSON OR ENTITY IN ANY COUNTRY.
Table Of Contents _______________________________
References ___________________________________________________________________________3
1.0 Overview ________________________________________________________________________3
1.1 Goals of a Plug and Play System BIOS
4
1.2 Enhancements to the current BIOS architecture
5
1.3 Elements of the Plug and Play BIOS architecture
6
Plug and Play BIOS Specification 1.0A
1.3.1 Bi-modal functionality
1.3.2 OS Independence
1.3.3 Expandability
1.4 Installation Structure
Page 2
6
6
6
7
2.0 System BIOS Initialization __________________________________________________________7
2.1 System BIOS POST Requirements
7
2.1.1 System Board Storage Requirements
8
2.1.2 System BIOS Resource Management
9
2.1.3 Isolating Committed Resources
9
2.1.4 System BIOS Resource Allocation
9
2.2 Plug and Play ISA Card Support
11
2.2.1 Assigning CSN to Plug and Play ISA cards
11
2.2.2 Initializing Plug and Play ISA Cards
11
2.3 BIOS POST Option ROM Initialization
12
2.4 Transferring Control to the Operating System
13
2.5 POST Execution flow
13
3.0 Option ROM Support _____________________________________________________________16
3.1 Option ROM Header
16
3.2 Expansion Header for Plug and Play
17
3.3 Option ROM Initialization
22
3.4 Option ROM Initialization flow
23
3.5 ISA Option ROMs and Resource Mapping
24
3.6 Error Recovery: Returning to the Boot flow
24
4.0 Configuration Support ____________________________________________________________25
4.1 System Device Configuration List
25
4.2 System Device Node Definition
25
4.3 Plug and Play BIOS Functions
29
4.4 Plug and Play Installation Check
29
4.4.1 System BIOS Plug and Play Compliance - "$PnP"
32
4.5 System Configuration Interface
34
4.5.1 Function 0 - Get Number of System Device Nodes
35
4.5.2 Function 1 - Get System Device Node
36
4.5.3 Function 2 - Set System Device Node
38
4.6 Event Notification Interface
40
4.6.1 Function 3 - Get Event
42
4.6.2 Function 4 - Send Message
43
4.6.3 Function 5 - Get Docking Station Information
47
4.6.4 Function 6 - Reserved
49
4.6.5 Function 7 - Reserved
49
4.6.6 Function 8 - Reserved
49
4.7 Extended Configuration Services
50
4.7.1 Function 9 - Set Statically Allocated Resource Information
51
4.7.2 Function 0Ah - Get Statically Allocated Resource Information
53
4.7.3 Function 40h - Get Plug & Play ISA Configuration Structure
54
4.7.4 Function 41h - Get Extended System Configuration Data (ESCD) Info
56
4.7.5 Function 42h - Read Extended System Configuration Data (ESCD)
56
4.7.6 Function 43h - Write Extended System Configuration Data (ESCD)
57
4.8 Power Management Services
58
4.8.1 Function 0Bh - Get APM ID Table
58
Plug and Play BIOS Specification 1.0A
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Appendix A: Generic Option ROM Headers _____________________________________________61
Appendix B: Device Driver Initialization Model___________________________________________62
Appendix C: Return Codes____________________________________________________________64
Plug and Play BIOS Specification 1.0A
Page 4
References _____________________________________
Plug and Play ISA Specification Version 1.0A May 5, 1994
Send email to [email protected] to obtain a copy.
EISA Specification Version 3.12
Contact BCPR Services Inc to obtain a copy.
Extended System Configuration Data Specification Version 1.02a
Contact Intel Corporation to obtain a copy.
Device Identifier Reference Table & Device Type Code Table
Browse the PlugPlay forum on CompuServe to obtain a copy.
1.0 Overview ___________________________________
This Plug and Play BIOS Specification defines new functionality to be provided in a PC compatible
system BIOS to fulfill the goals of Plug and Play. To achieve these goals, several new components have
been added to the System BIOS. Two key areas that are addressed by the System BIOS are resource
management and runtime configuration.
Resource management provides the ability to manage the fundamental system resources which include
DMA, Interrupt Request Lines (IRQs), I/O and Memory addresses. These resources, termed system
resources, are in high demand and commonly are over-allocated or allocated in a conflicting manner in
ISA systems, leading to bootstrap and system configuration failures. A plug and play system BIOS will
play a vital role in helping to manage these resources and ensure a successful launch of the operating
system.
In its role as resource manager, a Plug and Play BIOS takes on the responsibility for configuring Plug and
Play cards, as well as systemboard devices during the power-up phase. After the POST process is
complete, control of the Plug and Play device configuration passes from the system BIOS to the system
software. The BIOS does, however, provide configuration services for systemboard devices even after the
POST process is complete. These services are known as Runtime Services.
Runtime configuration is a concept that has not previously existed in a System BIOS before. The system
BIOS has not previously provided the ability to dynamically change the resources allocated to systemboard
devices after the operating system has been loaded. The Plug and Play BIOS Specification provides a
mechanism whereby a Plug and Play operating system may perform this resource allocation dynamically
at runtime. The operating system may directly manipulate the configuration of devices which have
traditionally been considered static via a System BIOS device node structure.
In addition, a Plug and Play System BIOS may also support event management. By means of the
interfaces outlined in this document, the System BIOS may communicate the insertion and removal of
newly installed devices which have been added to the system at runtime. The event management support
defined by this specification are specific to devices controlled by the system BIOS, such as docking a
notebook system to, or undocking it from, an expansion base. This event management does not
encompass the insertion and removal of devices on the various expansion busses.
This document describes the BIOS support necessary for both systemboards and add-in boards with
Option ROMs.
1.1 Goals of a Plug and Play System BIOS
Considering the scope of Plug and Play, the following are the goals of the Plug and Play BIOS
Specification.
Maximize ISA compatibility
Plug and Play BIOS Specification 1.0A
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This is the key consideration in a system BIOS. It is considered unacceptable to change the
architecture of a System BIOS to prevent the thousands of ISA cards and software programs that
rely on the system BIOS for services.
Eliminate resource conflicts during the POST procedure
A common problem that plagues many ISA systems today is the fact that there are a lot more
devices available than there are system resources. In this environment, devices are bound to have
conflicting resources. The system BIOS will now play a key role to help prevent these resource
conflicts by not enabling devices which conflict with the primary boot devices, and relocating boot
devices, if necessary, to allow a successful load of the operating system. It is the role of the
operating system to provide support for communicating irreconcilable resource conflicts to the
user.
Support Plug and Play ISA cards
A Plug and Play system BIOS is responsible for the isolation, enumeration, and optional
configuration of Plug and Play ISA cards. These cards, which provide information on their
resource requirements and permit software to configure those resources, will allow the system
BIOS to arrive at a conflict free configuration necessary to load the operating system.
Allow dynamic configuration of systemboard devices
Systemboard devices have traditionally been treated as having somewhat static configurations. It is
a goal of the Plug and Play BIOS specification to provide a standard mechanism whereby
systemboard devices may be configured dynamically by system software. This will grant
configuration management software a great deal of flexibility when system resources are in
demand and alternate configurations are necessary.
Note: Dynamic device configuration requires explicit device driver support.
Provide system event notification
The system BIOS is capable of detecting certain hardware events that could affect the system
configuration. By providing an event notification mechanism, an operating system can recognize
the event and process any necessary configuration changes.
Plug and Play BIOS Specification 1.0A
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Hardware and Operating System independence
The extensions to the system BIOS isolate the systemboard hardware through well defined
interfaces and structures. The system device nodes represent devices that are controlled by the
system BIOS. The operating system requires no specific knowledge of the systemboard in order to
control these devices, and instead relies on the system BIOS to isolate it from the underlying
hardware.
1.2 Enhancements to the current BIOS architecture
The Plug and Play BIOS Specification attempts to make several improvements to the current PC system
BIOS architecture to achieve the goals stated previously.
•
Perform resource allocation and conflict resolution at POST time.
The current System BIOS Architecture performs no such resource management at POST time. The
goal is to increase the probability of successfully bootstrapping into the OS by specifying resource
management at POST time.
•
Actively monitor the INT 19h bootstrap vector
The current System BIOS Architecture allows option ROMs to hook INT 19h indiscriminately. By
actively monitoring control of INT 19h, the System BIOS may regain control of the Bootstrap
process to ensure that the Operating System is loaded from the proper device and in the proper
manner.
•
Provide a mechanism for Remote Program Load
The current architecture provides no specific support for RPL. Consequently, RPL devices must
resort to hooking the INT 19h bootstrap vector or INT 18h, the alternate bootstrap vector. Hooking
these vectors can interfere with system specific security features, as well as result in bootstrap
failures. The method and support for booting from RPL devices is beyond the scope of the Plug
and Play BIOS Specification. A separate specification should define explicit support for RPL
devices.
•
Provide Runtime Configuration Support
Proprietary techniques exist to support device resource configuration and reporting. The Plug and
Play BIOS Specification defines specific, standard interfaces whereby configuration software may
identify and configure devices on the systemboard.
•
Provide Dynamic Event Notification
A further extension of the Runtime Configuration Support allows the System BIOS to report
dynamic configuration events to the Plug and Play software such that new devices added into the
system may be resource managed. This dynamic event notification interface is specific to devices
controlled by the system BIOS. It does not encompass the insertion and removal of devices on the
various expansion busses
Plug and Play BIOS Specification 1.0A
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1.3 Elements of the Plug and Play BIOS architecture
1.3.1 Bi-modal functionality
All Plug and Play BIOS Services which are accessible at runtime support a bi-modal interface. The two
modes supported are 16-bit Real Mode and 16-bit Protected Mode. These two modes are sufficient to
support a wide variety of operating environments. Real Mode interfaces are defined in terms of the
segment and offset of the service entry point.
Protected Mode interfaces specify the code segment base address so that the caller can construct the
descriptor from the segment base address before calling the interface from protected mode. The offset
value is the offset of the entry point. It is assumed that the 16-Bit Protected Mode interface is sufficient
for 32-Bit Protected Mode callers. However, it is important to note that Plug and Play BIOS functions
will access arguments on the stack as a 16-bit stack frame. Therefore, the caller must ensure that the
function arguments are pushed onto the stack as 16-bit values and not 32-bit values. For function
arguments that are pointers, the pointer offset and data should be contained within the first 64K bytes of
the segment. Refer to section 4.4 Plug and Play Installation Check for a complete description of the bimodal interface.
1.3.2 OS Independence
The Plug and Play BIOS services, which are accessible during normal system operation, are defined in a
manner independent from the operating system. The BIOS System Device Nodes are a compact form of
a device node tailored specifically to the configuration of systemboard devices.
A Plug and Play OS which complies with the general framework of the Plug and Play Architecture
requires a software isolation/translation layer between the System BIOS and the OS.
The isolation/translation software performs the task of translating the generic BIOS interfaces defined in
this specification into those required to support configuration management in the desired operating
environment.
1.3.3 Expandability
Throughout the Plug and Play BIOS Specification care was taken to provide a mechanism for extensibility
of this specification. All significant structures and interfaces are defined with revision identifiers. These
revision identifiers provide a mechanism whereby the interfaces defined may be extended so long as the
interfaces remain backward compatible to the original specification.
1.4 Installation Structure
Section 4.4 of this specification defines the Plug and Play installation check procedure and structure. This
mechanism defines a structure which may be located on any 16-byte boundary within the System BIOS
address space of 0F0000h - 0FFFFFh. Software which must determine if it is operating on a platform
supporting a Plug and Play BIOS, should scan the specified address space searching for the ASCII string
"$PnP" on 16-byte boundaries. If the software identifies such a string on a 16-byte boundary, it must
validate that it has indeed found a Plug and Play Installation Check Structure by verifying the structure's
checksum and validate either the version field or the length field or both. A valid checksum indicates that
the system BIOS provides all of the required functions of the Plug and Play System BIOS specification.
Specifying this structure in this manner permits it to float anywhere in the specified address range. This
permits the System BIOS developer to locate the structure within their ROM without having to be
concerned about it interfering with other structures that they may have specified at fixed addresses.
Plug and Play BIOS Specification 1.0A
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2.0 System BIOS Initialization _____________________
The Power On Self Test (POST) procedure of a system BIOS is designed to identify, test, and configure
the system in preparation for starting the operating system. At the completion of POST, the PC
compatible system BIOS attempts to have all of the appropriate devices enabled in order for them to be
properly recognized and functioning when the operating system loads.
Over the years, PC compatible systems have become much more sophisticated in terms of the bus
architectures supported and the devices attached. As these PC compatible systems have evolved and
become more sophisticated, so has the system BIOS, which is responsible for the initial configuration of
these devices. However, one component has remained relatively constant in a PC compatible system. This
is the system resources. System resources, as described in this document include DMA channels,
Interrupt Request Lines (IRQs), I/O addresses, and memory.
As the sophistication of these systems increases with more and more devices, the possibility of resource
conflicts also increase, leading to a possible boot or system failure. The Plug and Play BIOS specification
is defined to solve the problems that occur with resource conflicts. Specifically, the Plug and Play BIOS is
taking on a new responsibility to ensure that the operating system is loaded with a conflict free set of
resources, as well as indicating to the operating system the resources that are currently used by
systemboard devices.
2.1 System BIOS POST Requirements
In order to achieve the goals of Plug and Play, the system BIOS POST is responsible for achieving the
requirements listed below:
• Maintain ISA POST compatibility
The important issue of this broad requirement is that a Plug and Play system BIOS is responsible for
the same POST requirements of an existing PC compatible system BIOS. This document focuses only
on the enhancements necessary to a PC compatible system BIOS and assumes that the basic BIOS
POST initialization is still performed.
Plug and Play BIOS Specification 1.0A
•
•
•
•
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Configuration of all static devices known to system BIOS
At a minimum, this includes system board devices. It can also include Plug and Play ISA Cards and
devices located on EISA, ISA, PCI, or any of the other static bus architectures available. How this
configuration is completed will be described in a later section.
BIOS POST Resource arbitration
The system BIOS must now be aware of system resource usage. Using the information provided
through runtime services (described in a later section), along with resource information known to the
system BIOS, critical resource conflicts can be avoided. Loading the operating system with a
conflicting device disabled is better than causing a resource conflict and a possible system failure.
Initialization of the Initial Program Load (IPL) device
It is the responsibility of the system BIOS POST to make sure that resources for the IPL device get
allocated correctly in anticipation of a successful load of the operating system. If “disabled” IPL
devices are needed to achieve boot, then the system BIOS POST should take the initiative to reenable
"disabled" IPL devices in an intelligent sequence to provide the best opportunity for system boot.
Support for both Plug and Play and Non-Plug and Play Operating Systems
The Plug and Play system BIOS POST must configure the system to operate with both Plug and Play
aware, as well as non-Plug and Play operating system. In non-Plug and Play environments, either the
system BIOS or the appropriate system software (device drivers) must configure all devices (Plug and
Play ISA Cards, PCI devices, etc.). This will allow all environments to load exactly as they would on
a standard PC compatible systems. However, in a Plug and Play environment, the system BIOS can
now assist the operating system to perform features such as runtime configuration of system board
devices and event recognition when system board devices have changed.
2.1.1 System Board Storage Requirements
Adding optional static resource allocation capabilities to the Plug and Play BIOS POST procedure will
require additional storage. This storage is necessary for maintaining information about system resources
that have been explicitly assigned to the boot devices as well as the system resources being utilized by ISA
devices in the system. The amount of storage that will be necessary is platform specific, but could exceed
the amount of storage normally available in PC compatible systems.
If the static resource allocation option is implemented, then the system BIOS is required to follow the
function interface defined later in this document. This interface provides the mechanism for system
software to specify the information about these system resources. How the information is actually stored
in the nonvolatile storage on the system is left up to the BIOS implementor.
This new storage must be readily available and dependable during the system BIOS POST for the system
BIOS to provide effective resource allocation. The type of storage, which can be either Flash, CMOS,
NVRAM, or some other type of nonvolatile storage, and the amount of additional storage needed will vary
depending on the systemboard requirements. It is left to the systemboard manufacturer to make available
additional storage to the system BIOS, and the BIOS suppliers responsibility to manage and allocate this
nonvolatile storage.
2.1.2 System BIOS Resource Management
A key element of a Plug and Play BIOS is to provide accurate resource management. Management of
system resources, which includes DMA, IRQs, I/O, and Memory, is vital to a system BIOS POST if it is
to guarantee successful loading of the operating system. Unfortunately, there is no clear defined
procedure for how these system resources should be allocated by the system BIOS. This section will
describe how the system BIOS POST can manage resources and will outline the different methods that
can be used to allocate the system resources.
Plug and Play BIOS Specification 1.0A
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2.1.3 Isolating Committed Resources
The first step to resource management is to determine system resources that are statically allocated to
devices in the system. These resources can be located on ISA cards, systemboard devices, or any other
device present in the system. Unfortunately, it is very difficult, if not impossible, to accurately determine
the resources used, unless these devices provide information about the system resources they will use.
With this in mind, it is necessary for an external program to help isolate the resources that these devices
are using. How this external program determines the resources consumed by these devices is beyond the
scope of this document. However, what is within the scope is the interface that the system BIOS provides
to indicate resources that are allocated to the ISA devices.
Function 09h, Set Statically Allocated Resource Information, of the runtime services is designed to
support an external program that can indicate the resources that are allocated to the static ISA devices in
the system. Through this interface, the system resources utilized by these ISA devices will be saved in
nonvolatile storage. This will allow the system BIOS to ensure the configuration of the boot devices in the
system do not conflict with any static ISA devices during the POST configuration process.
2.1.4 System BIOS Resource Allocation
There are three fundamental methods that the system BIOS POST can use to allocate resources to devices.
They are:
Static Resource Allocation - Allocate resources based on the last working configuration of the system.
This requires that the resources assigned to specific devices in the system be saved in nonvolatile storage
on the system. This configuration information must be accessible to the system BIOS during POST. The
interface and format for storing the resource information explicitly assigned to every device in the system
may be stored in an OEM specific format or it may follow the Extended System Configuration Data
(ESCD) format. Refer to the ESCD Specification for a complete description of the ESCD and its
interfaces. The ESCD interface provides a mechanism for allowing system software the ability to lock the
system resources allocated to specific devices in the system. This will allow the configuration of devices
to remain consistent between operating sessions.
Dynamic Resource Allocation - Dynamically auto-configure the systemboard and Plug and Play devices in
the system. At a minimum, the system BIOS must ensure that only the primary boot devices are properly
configured to boot the system software. When loaded, the system software is responsible for dynamically
configuring all remaining devices. Depending on the system's architecture, the BIOS may have to
implement Function 09h, Set Statically Allocated Resource Information, to guarantee a conflict free boot
device configuration.
Combined Static and Dynamic Resource Allocation - Allocating resources based on the configuration
information specified for the last working configuration for the system, as well as dynamically configuring
the Plug and Play devices in the system, which were not specified in the last working configuration
resource information.
A system BIOS can use any one of these methods for allocating system resources to the devices in the
system. What is important for each of these methods to work successfully is an accurate accounting of the
committed resources used in the system. It is important to note that the primary responsibility for system
BIOS resource allocation is to ensure that the primary boot devices are configured properly to boot the
Plug and Play operating system. If the Plug and Play system BIOS chooses to only configure the primary
boot devices, the appropriate system software or Plug and Play operating system will be responsible for
configuring any unconfigured devices.
Static Resource Allocation
This method assumes that the system software has specified the appropriate resource configuration
information to the system BIOS for ALL devices in the system. As mentioned above, it is an option that
the system BIOS interface, for allowing system software to provide the last working configuration
information to the system BIOS, follows the Extended System Configuration Data (ESCD) format.
Once this information has been saved by the system BIOS, this information is used by the BIOS during
POST to allocate resources to all of the configurable devices that are known to the system BIOS.
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There are certain benefits that can be realized by supporting Static Resource Allocation. First, the
configuration of every device in the system is saved in nonvolatile storage which allows the BIOS to
allocate the appropriate resources to the devices in the system during POST. This allows the last working
configuration to be maintained from boot to boot. Another benefit comes from the ability to explicitly
assign, or lock, the resources allocated to any Plug and Play card in the system. Static resource allocation
will require nonvolatile storage on the system for storing the resource allocation for each device in the
system.
Example: The EISA architecture is an example of an architecture which uses static resource allocation.
The EISA configuration utility is responsible for determining device resource allocations, then storing that
information for the BIOS. Upon initialization, the system BIOS accesses the stored device configurations
and subsequently programs each device accordingly. The system BIOS does not perform any conflict
detection or resolution.
Dynamic Resource Allocation
The method for dynamic resource allocation is for the system BIOS POST to dynamically allocate
resources to configurable devices using a procedure considered most desirable or effective to the system
BIOS. This method usually needs to know what resources are being used by static (old ISA) devices in the
system to work successfully. The system resources allocated to the static devices are registered with the
system BIOS through function 09h, Set Statically Allocated Resource Information, of the runtime
services.
The primary benefits of dynamic resource allocation are the minimal amount of nonvolatile storage
required and the flexibility in resource allocation provided to the Plug and Play devices installed in the
system. As mentioned above, the system BIOS needs to know the system resources being used by the
static devices for effective dynamic resource allocation. The system software must provide this
information through the Set Statically Allocated Resource Information function.
Example: An example of a system which supports dynamic resource allocation is one where the system
BIOS only stores information regarding static ISA devices (assuming that this information is supplied by
a configuration utility). Using this stored information, a system BIOS could use semi-intelligent
algorithms to configure the Plug and Play devices "around" the static ISA devices. Such a configuration is
dynamic because it is determined each time the system boots.
2.2 Plug and Play ISA Card Support
One responsibility of a Plug and Play BIOS during POST is to isolate and initialize all Plug and Play ISA
cards and assign them with a valid Card Select Number (CSN). Once a CSN is assigned, the system BIOS
can then designate resources to the Plug and Play ISA cards according to the resource allocation scheme
chosen for the system. While the configuration of the required Plug and Play ISA boot devices by the Plug
and Play BIOS is mandatory, all of the remaining Plug and Play devices may be configured dynamically
by the system software at boot. The system BIOS mayalso provide a mechanism for system software to
explicitly allocate system resources to the Plug and Play ISA cards in the system. For example, the system
BIOS could provide support for allocating the last working configuration.
2.2.1 Assigning CSN to Plug and Play ISA cards
Early in the POST process, a Plug and Play system BIOS should always perform the isolation process for
Plug and Play ISA cards as specified in the Plug and Play ISA specification V1.00. This process should
be performed regardless if CSNs have already been assigned to the Plug and Play Devices. This will
guarantee accurate initialization of each Plug and Play device during the start of the operating system.
The Plug and Play ISA specification requires that CSNs must be assigned sequentially starting at one and
continuing in the order that each Plug and Play ISA card is isolated.
A responsibility of the system BIOS is to maintain the last assigned CSN. This information will be
returned through function 40h, Get ISA Configuration Structure, of the Plug and Play runtime services.
Programs that want to scan through the CSNs looking for their adapter will need to know the last CSN
assigned.
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On systems with a dynamic ISA bus, like portables, function 40h will be more flexible. When an ISA bus
is present, the information returned by function 40h will always be valid after a cold boot. On a cold boot
with no ISA bus present, function 40h will return zeros. After an ISA warm/hot dock, the function 40h
information will also be valid, if the plug and play BIOS isolates and enumerates the plug and play
adapter cards before returning control to the plug and play operating system. If the BIOS does not reenumerate after an ISA warm/hot dock event, then the information returned by function 40h will be zeros.
After an ISA undock event, this information will also be zeros.
2.2.2 Initializing Plug and Play ISA Cards
After CSNs have been assigned, all Plug and Play ISA devices should be inactive. Later in POST when
the system resources have been determined, Plug and Play ISA cards will be enabled as determined by the
system's allocation scheme. This means that at least all of the Plug and Play ISA bootable cards will be
configured and enabled.
During the POST sequence, the system BIOS will need to select an Input, Output, and Initial Program
Load (IPL) device. Based on the other devices in the system, any Plug and Play device that is a boot device
will get enabled to provide the boot services. Plug and Play devices that are not boot devices may get
enabled later in POST if, and only if they can be enabled without creating a resource conflict.
The method used to allocate resources to the Plug and Play ISA cards depends on the resource allocation
method described in the section above. If Static Resource Allocation is being used then the Plug and Play
ISA devices will be initialized according to the information specified for the last working configuration.
If Dynamic Resource Allocation is being used then resource information available from the Plug and Play
ISA card will be used to configure the device during the BIOS POST process.
2.3 BIOS POST Option ROM Initialization
One of the new features of the Plug and Play BIOS architecture is the enhancements to the ISA Option
ROM architecture. This new interface will help couple the system BIOS closely with the Plug and Play
option ROM to assist the system BIOS in completing the POST configuration process. For details about
the Plug and Play option ROM enhancements, refer to the section on the Plug and Play Option ROM.
This section describes how the system BIOS will initialize both standard ISA and Plug and Play Option
ROMs.
All ISA option ROMs that are not Plug and Play compatible will be initialized by the Plug and Play BIOS
POST using the exact procedure used in existing PC compatible systems. This procedure is performed by
scanning the C0000h to EFFFFh address space on 2K boundaries searching for a 55AAh header. Once
located, the module is checksummed to determine if the structure is valid and, if valid, the option ROM is
initialized by making a far call to offset 03h within the segment.
There are two different environments that Plug and Play compliant option ROMs could be installed in.
The first is a standard PC compatible system that does not have a Plug and Play compatible system BIOS.
The second environment is a system that has a Plug and Play system BIOS. The option ROM can
determine which environment it is installed in by examining the register information passed to the option
ROM's initialization routine. It is able to perform this check because the Plug and Play BIOS will provide
the following information:
Entry: ES:DI Pointer to System BIOS Plug and Play Installation Check Structure (See Section 4.4)
The following registers will only be initialized for Plug and Play ISA devices:
BX
Card Select Number for this card, FFFFh if this device is not ISA Plug and Play.
DX
Read Data Port address, FFFFh if there are no ISA Plug and Play devices in the system.
For other bus architectures, refer to the appropriate specification. For example, the PCI Local Bus
Specification R2.0 published by the PCI SIG specifies AH=Bus number and AL=Device Function number
as parameters for Option ROM initialization.
On a system that does not have a Plug and Play compatible system BIOS, ES:DI would not point to a valid
Plug and Play Installation Check Structure . Therefore, by validating the contents of the data pointed to in
ES:DI, the option ROM can determine whether it is being initialized from a Plug and Play or non-Plug
Plug and Play BIOS Specification 1.0A
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and Play system BIOS. Once the option ROM has determined the environment it is installed in, it can
perform the proper steps for initialization.
In the first environment, which is a standard PC compatible system that does not have a Plug and Play
compatible system BIOS, the ISA option ROM scan will be performed and the Plug and Play option ROM
should initialize exactly as if it was a standard ISA option ROM.
In the second environment, where the system has a Plug and Play system BIOS, the option ROM will
recognize the Plug and Play installation check structure and perform the initialization as specified in
section 3, which describes the option ROM support. Option ROM initialization routines can not depend
on any of the Plug and Play runtime functions to be available until after INT19 has been invoked at the
end of the POST process.2.4 Interrupt 19H Execution
Interrupt 19h, commonly referred to as the system bootstrap loader, is responsible for loading and
executing the first sector of the operating system. This bootstrap sequence is the final component of the
system BIOS POST before control is passed onto the operating system. In a PC system, the Initial
Program Load (IPL) device can easily be any device supported by an option ROM if it intercepts Interrupt
13h and provides these services. However, some option ROMs have gone even further and captured
Interrupt 19h to control the bootstrap process.
An Option ROM which takes control of Interrupt 19h presents a major problem to a Plug and Play system
BIOS. The system BIOS can no longer control which device will be the Initial Program Load (IPL)
device since it no longer controls the bootstrap sequence. Given this dilemma, the system BIOS POST
will recapture Interrupt 19h away from an option ROM if the primary Initial Program Load (IPL) device
is either a Plug and Play ISA device or a device that is known to the system BIOS (e.g., ATA compatible
IDE fixed disk).
One particularly interesting situation occurs when the system BIOS has recaptured Interrupt 19h and then
determines that it cannot load the operating system due to invalid media or other problems. In this case,
the Plug and Play system BIOS will restore the last captured Interrupt 19h vector and reinitiate the
Interrupt 19h boot sequence.
2.4 Transferring Control to the Operating System
The very last function of the system BIOS POST after loading and validating the operating system boot
sector is to transfer control. In an ISA system, control is transferred without any parameters. In a Plug
and Play system BIOS, parameters will be passed to the operating system. The parameters are:
Entry: ES:DI Pointer to System BIOS Plug and Play Installation Check Structure (See section 4.4)
DL
Physical device number the OS is being loaded from (e.g. 80h, assuming the device
supports INT 13H interface.)
In a non-Plug and Play operating environment this information will have no meaning. However, a Plug
and Play operating system will look for a Plug and Play system BIOS and use any information it may
need. The physical device number is passed to allow the operating system to continue to load from the
current physical device, instead of assuming a physical device of 00h or 80h.
2.5 POST Execution flow
The following steps outline a typical flow of a Plug and Play system BIOS POST. All of the standard ISA
functionality has been eliminated for clarity in understanding the Plug and Play POST enhancements.
Step 1 Disable all configurable devices
Any configurable devices known to the system BIOS should be disabled early in the POST
process.
Step 2 Identify all Plug and Play ISA devices
Assign CSNs to Plug and Play ISA devices but keep devices disabled. Also determine which
devices are boot devices.
Step 3 Construct an initial resource map of allocated resources
Construct a resource map of resources that are statically allocated to devices in the system. If the
system software has explicitly specified the system resources assigned to ISA devices in the
Plug and Play BIOS Specification 1.0A
Page 14
system through the Set Statically Allocated Resource Information function, the system BIOS
will create an initial resource map based on this information.
If the BIOS implementation provides support for saving the last working configuration and the
system software has explicitly assigned system resources to specific devices in the system, then
this information will be used to construct the resource map. This information will also be used to
configure the devices in the system.
Plug and Play BIOS Specification 1.0A
Step 4
Step 5
Step 6
Step 7
Step 8
Step 9
Page 15
Enable Input and Output Devices
Select and enable the Input and Output Device. Compatibility devices in the system that are not
configurable always have precedence. For example, a standard VGA adapter would become the
primary output device. If configurable Input and Output Devices exists, then enable these devices
at this time. If Plug and Play Input and Output Devices are being selected, then initialize the
option ROM, if it exists, using the Plug and Play option ROM initialization procedure (See
section 3).
Perform ISA ROM scan
The ISA ROM scan should be performed from C0000h to EFFFFh on every 2K boundary. Plug
and Play Option ROMs are disabled at this time (except input and output boot devices) and will
not be included in the ROM scan.
Configure the IPL device
If a Plug and Play device has been selected as the IPL device, then use the Plug and Play Option
ROM procedure to initialize the device. If the IPL device is known to the system BIOS, then
ensure that interrupt 19h is still controlled by the system BIOS. If not, recapture interrupt 19h
and save the vector.
Enable Plug and Play ISA and other Configurable Devices
If a static resource allocation method is used, then enable the Plug and Play ISA cards with
conflict free resource assignments. Initialize the option ROMs and pass along the defined
parameters. All other configurable devices should be enabled, if possible, at this time.
If a dynamic resource allocation method is used, then enable the bootable Plug and Play ISA
cards with conflict free resource assignments and initialize the option ROMs.
Initiate the Interrupt 19H IPL sequence
Start the bootstrap loader. If the operating system fails to load and a previous ISA option ROM
had control of the interrupt 19h vector, then restore the interrupt 19h vector to the ISA option
ROM and re-execute the Interrupt 19h bootstrap loader.
Operating system takes over resource management
If the loaded operating system is Plug and Play compliant, then it will take over management of
the system resources. It will use the runtime services of the system BIOS to determine the
current allocation of these resources. It is assumed that any unconfigured Plug and Play devices
will be configured by the appropriate system software or the Plug and Play operating system.
3.0 Option ROM Support_________________________
This section outlines the Plug and Play Option ROM requirements. This Option ROM support is directed
specifically towards boot devices; however, the Static Resource Information Vector permits non-Plug
and Play devices which have option ROMs to take advantage of the Plug and Play Option ROM expansion
header to assist a Plug and Play environment whether or not it is a boot device. A boot device is defined
as any device which must be initialized prior to loading the Operating System. Strictly speaking, the only
required boot device is the Initial Program Load (IPL) device upon which the operating system is stored.
However, the definition of boot devices is extended to include a primary Input Device and a primary
Output device. In some situations these I/O devices may be required for communication with the user.
All new Plug and Play devices that support Option ROMs should support the Plug and Play Option ROM
Header. In addition, all non-Plug and Play devices may be "upgraded" to support the Plug and Play
Option ROM header as well. While these static ISA devices will still not have software configurable
resources, the Plug and Play Option ROM Header will greatly assist a Plug and Play System BIOS in
identification and selection of the primary boot devices.
It is important to note that the Option ROM support outlined here is defined specifically for computing
platforms based on the Intel X86 family of microprocessors and may not apply to systems based on other
types of microprocessors.
Plug and Play BIOS Specification 1.0A
Page 16
3.1 Option ROM Header
The Plug and Play Option ROM Header follows the format of the Generic Option ROM Header extensions
described in Appendix A. The Generic Option ROM header is a mechanism whereby the standard ISA
Option ROM header may be expanded with minimal impact upon existing Option ROMs. The pointer at
offset 1Ah may point to ANY type of header. Each header provides a link to the next header; thus, future
Option ROM headers may use this same generic pointer and still coexist with the Plug and Play Option
ROM header. Each Option ROM header is identified by a unique string. The length and checksum bytes
allow the System BIOS and/or System Software to verify that the header is valid.
Standard Option ROM Header:
Offset
Length
Value
Description
0h
2h
AA55h
Signature
Standard
2h
1h
Varies
Option ROM Length
Standard
3h
4h
Varies
Initialization Vector
Standard
7h
13h
Varies
Reserved
Standard
1Ah
2h
Varies
Offset to Expansion Header Structure
New for Plug and
Play
Signature - All ISA expansion ROMs are currently required to identify themselves with a signature
WORD of AA55h at offset 0. This signature is used by the System BIOS as well as other software to
identify that an Option ROM is present at a given address.
Length - The length of the option ROM in 512 byte increments.
Initialization vector - The system BIOS will execute a FAR CALL to this location to initialize the Option
ROM. A Plug and Play System BIOS will identify itself to a Plug and Play Option ROM by passing a
pointer to a Plug and Play Identification structure when it calls the Option ROM's initialization vector. If
the Option ROM determines that the System BIOS is a Plug and Play BIOS, the Option ROM should not
hook the input, display, or IPL device vectors (INT 9h, 10h, or 13h) at this time. Instead, the device
should wait until the System BIOS calls the Boot Connection vector before it hooks any of these vectors.
Note: A Plug and Play device should never hook INT 19h or INT 18h until its Boot Connection Vector,
offset 16h of the Expansion Header Structure (section 3.2), has been called by the Plug and Play system
BIOS.
If the Option ROM determines that it is executing under a Plug and Play system BIOS, it should return
some device status parameters upon return from the initialization call. See the section on Option ROM
Initialization for further details.
The field is four bytes wide even though most implementations may adhere to the custom of defining a
simple three byte NEAR JMP. The definition of the fourth byte may be OEM specific.
Reserved - This area is used by various vendors and contains OEM specific data and copyright strings.
Offset to Expansion Header - This location contains a pointer to a linked list of Option ROM expansion
headers. Various Expansion Headers (regardless of their type) may be chained together and accessible via
this pointer. The offset specified in this field is the offset from the start of the option ROM header.
Plug and Play BIOS Specification 1.0A
Page 17
3.2 Expansion Header for Plug and Play
Offset
0h
Length
4 BYTES
04h
05h
06h
08h
09h
0Ah
0Eh
10h
12h
15h
16h
BYTE
BYTE
WORD
BYTE
BYTE
DWORD
WORD
WORD
3 BYTE
BYTE
WORD
Value
$PnP
(ASCII)
Varies
Varies
Varies
00h
Varies
Varies
Varies
Varies
Varies
Varies
Varies
18h
WORD
Varies
1Ah
WORD
Varies
1Ch
1Eh
WORD
WORD
0000h
Varies
Description
Signature
Structure Revision
Length (in 16 byte increments)
Offset of next Header (0000h if none)
Reserved
Checksum
Device Identifier
Pointer to Manufacturer String (Optional)
Pointer to Product Name String (Optional)
Device Type Code
Device Indicators
Boot Connection Vector - Real/Protected mode
(0000h if none)
Disconnect Vector - Real/Protected mode (0000h if
none)
Bootstrap Entry Point - Real/Protected mode (0000h
if none)
Reserved
Static Resource Information Vector- Real/Protected
mode (0000h if none)
Generic
01h
Generic
Generic
Generic
Generic
PnP Specific
PnP Specific
PnP Specific
PnP Specific
PnP Specific
PnP Specific
PnP Specific
PnP Specific
PnP Specific
PnP Specific
Signature - All Expansion Headers will contain a unique expansion header identifier. The Plug and Play
expansion header's identifier is the ASCII string "$PnP" or hex 24 50 6E 50h (Byte 0 = 24h ... Byte 3 =
50h).
Structure Revision - This is an ordinal value that indicates the revision number of this structure only and
does not imply a level of compliance with the Plug and Play BIOS version.
Length - Length of the entire Expansion Header expressed in sixteen byte blocks. The length count starts
at the Signature field.
Offset of Next Header - This location contains a link to the next expansion ROM header in this Option
ROM. If there are no other expansion ROM headers, then this field will have a value of 0h. The offset
specified in this field is the offset from the start of the option ROM header.
Reserved - Reserved for Expansion
Checksum - Each Expansion Header is checksummed individually. This allows the software which
wishes to make use of an expansion header (in this case, the system BIOS) the ability to determine if the
expansion header is valid. The method for validating the checksum is to add up all byte values in the
Expansion Header, including the Checksum field, into an 8-bit value. A resulting sum of zero indicates a
valid checksum operation.
Device Identifier - This field contains the Plug and Play Device ID.
Pointer to Manufacturer String (Optional) - This location contains an offset relative to the base of the
Option ROM which points to an ASCIIZ representation of the board manufacturer's name. This field is
optional and if the pointer is 0 (Null) then the Manufacturer String is not supported.
Pointer to Product Name String (Optional) - This location contains an offset relative to the base of the
Option ROM which points to an ASCIIZ representation of the product name. This field is optional and if
the pointer is 0 (Null) then the Product Name String is not supported.
Device Type Code - This field contains general device type information that will assist the System BIOS
in prioritizing the boot devices.
The Device Type code is broken down into three byte fields. The byte fields consist of a Base-Type code
that indicates the general device type. The second byte is the device Sub-Type and its definition is
Plug and Play BIOS Specification 1.0A
Page 18
dependent upon the Base-Type code. The third byte defines the specific device programming interface,
IF.-Type, based on the Base-Type and Sub-Type.
Refer to Appendix B for a description of Device Type Codes.
Device Indicators - This field contains indicator bits that identify the device as being capable of being
one of the three identified boot devices: Input, Output, or Initial Program Load (IPL).
Bit
Description
7
A 1 indicates that this ROM supports the Device Driver Initialization Model
6
A 1 indicates that this ROM may be Shadowed in RAM
5
A 1 indicates that this ROM is Read Cacheable
4
A 1 indicates that this option ROM is only required if this device is selected as a boot
device.
3
Reserved (0)
2
A 1 in this position indicates that this device is an Initial Program Load (IPL) device.
1
A 1 in this position indicates that this device is an Input device.
0
A 1 in this position indicates that this device is a Display device.
Boot Connection Vector (Real/Protected mode) - This location contains an offset from the start of the
option ROM header to a routine that will cause the Option ROM to hook one or more of the primary
input, primary display, or Initial Program Load (IPL) device vectors (INT 9h, INT 10h, or INT 13h),
depending upon the parameters passed during the call.
When the system BIOS has determined that the device controlled by this Option ROM will be one of the
boot devices (the Primary Input, Primary Display, or IPL device), the System ROM will execute a FAR
CALL to the location pointed to by the Boot Connection Vector. The system ROM will pass the
following parameters to the options ROM's Boot Connection Vector:
Plug and Play BIOS Specification 1.0A
Reg On Entry
AX
ES:DI
BX
DX
Page 19
Description
Provides an indication as to which vectors should be hooked by specifying the
type of boot device this device has been selected as.
Bit 7..3 Reserved(0)
Bit 2
1=Connect as IPL (INT 13h)
Bit 1
1=Connect as primary Video (INT 10h)
Bit 0
1=Connect as primary Input (INT 09h)
Pointer to System BIOS PnP Installation Check Structure (See section 4.4)
CSN for this card, ISA PnP devices only. If not an ISA PnP device then this
parameter will be set to FFFFh.
Read Data Port, (ISA PnP devices only. If no ISA PnP devices then this
parameter will be set to FFFFh.
Disconnect Vector (Real/Protected mode) - This vector is used to perform a cleanup from an unsuccessful
boot attempt on an IPL device. The system ROM will execute a FAR CALL to this location on IPL
failure.
Bootstrap Entry Vector (Real/Protected mode) - This vector is used primarily for RPL (Remote Program
Load) support. To RPL (bootstrap), the System ROM will execute a FAR CALL to this location. The
System ROM will call the Real/Protected Mode Bootstrap Entry Vector instead of INT 19h if:
a) The device indicates that it may function as an IPL device,
b) The device indicates that it does not support the INT 13h Block Mode interface,
c) The device has a non-null Bootstrap Entry Vector,
d) The Real/Protected Mode Boot Connection Vector is null.
The method for supporting RPL is beyond the scope of this specification. A separate specification should
define the explicit requirements for supporting RPL devices.
Reserved - Reserved for Expansion
Static Resource Information Vector - This vector may be used by non-Plug and Play devices to report
static resource configuration information. Plug and Play devices should not support the Static Resource
Information Vector for reporting their configuration information. This vector should be callable both
before and/or after the option ROM has been initialized. The call interface for the Static Resource
Information Vector is as follows:
Entry: ES:DI
Pointer to memory buffer to hold the device's static resource configuration information.
The buffer should be a minimum of 1024 bytes. This information should follow the
System Device Node data structure, except that the Device node number field should
always be set to 0, and the information returned should only specify the currently
allocated resources (Allocated resource configuration descriptor block) and not the
block of possible resources (Possible resource configuration descriptor block). The
Possible resource configuration descriptor block should only contain the END_TAG
resource descriptor to indicate that there are no alternative resource configuration
settings for this device because the resource configuration for this device is static. Refer
to the Plug and Play ISA Specification under the section labeled Plug and Play
Resources for more information about the resource descriptors. This data structure has
the following format:
Plug and Play BIOS Specification 1.0A
Field
Size of the device node
Device node number/handle
Device product identifier
Device type code
Device node attribute bit-field
Allocated resource configuration descriptor block
Possible resource configuration descriptor block should only specify the END_TAG resource
descriptor
Compatible device identifiers
Page 20
Size
WORD
BYTE
DWORD
3 BYTES
WORD
VARIABLE
2 BYTES
VARIABLE
Refer to section 4.2 for a complete description of the elements that make up the System Device Node data
structure.
For example, an existing, non-Plug and Play SCSI card vendor could choose to rev the SCSI board's
Option ROM to support the Plug and Play Expansion Header. While this card wouldn't gain any of the
configuration benefits provided to full hardware Plug and Play cards, it would allow Plug and Play
software to determine the devices configuration and thus ensure that Plug and Play cards will map around
the static SCSI board's allocated resources.
3.3 Option ROM Initialization
The System BIOS will determine if the Option ROM it is about to initialize supports the Plug and Play
interface by verifying the Structure Revision number in the device's Plug and Play Header Structure. For
all Option ROMs compliant with the 1.0 Plug and Play BIOS Specification, the System BIOS will call the
device's initialization vector with the following parameters:
Reg On Entry
Description
ES:DI
Pointer to System BIOS PnP Installation Check Structure (See section 4.4)
BX
CSN for this card, ISA PnP devices only. If not an ISA PnP device then this
parameter will be set to FFFFh.
DX
Read Data Port, (ISA PnP devices only. If no ISA PnP devices then this
parameter will be set to FFFFh.
For other bus architectures refer to the appropriate specification for register parameters on entry.
During initialization, a Plug and Play Option ROM may hook any vectors and update any data structures
required for it to access any attached devices and perform the necessary identifications and initializations.
However, upon exit from the initialization call, the Option ROM must restore the state of any vectors or
data structures related to boot devices (INT 9h, INT 10h, INT 13h, and associated BIOS Data Area [BDA]
and Extended BIOS Data Area [EBDA] variables).
Plug and Play BIOS Specification 1.0A
Page 21
Upon exit from the initialization call, Plug and Play Option ROMs should return some boot device status
information in the following format:
Return Status from Initialization Call:
AX Bit
Description
8
1 = IPL Device supports INT 13h Block Device format
7
1 = Output Device supports INT 10h Character Output
6
1 = Input Device supports INT 9h Character Input
5:4
00 = No IPL device attached
01 = Unknown whether or not an IPL device is attached
10 = IPL device attached
(RPL devices have a connection).
11 = Reserved
3:2
00 = No Display device attached
01 = Unknown whether or not a Display device is attached
10 = Display device attached
11 = Reserved
1:0
00 = No Input device attached
01 = Unknown whether or not an Input device is attached
10 = Input device attached
11 = Reserved
3.4 Option ROM Initialization flow
The following outlines the typical steps used to initialize Option ROMs during a Plug and Play system
BIOS POST:
Step 1 Initialize the boot device option ROMs.
This includes the Primary Input, Primary Output, and Initial Program Load (IPL) device option
ROMs.
Step 2 Initialize ISA option ROMs by performing ISA ROM scan
The ISA ROM scan should be performed from C0000h to EFFFFh on every 2k boundary. Plug
and Play option ROMs will not be included in the ROM scan.
Step 3 Initialize option ROMs for ISA devices which have a Plug and Play option ROM.
Typically, these devices will not provide support for dynamic configurability. However, the
resources utilized by these devices can be obtained through the Static Resource Information
Vector as described in section 3.2.
Step 4 Initialize option ROMs for Plug and Play cards which have a Plug and Play option ROM.
Step 5 Initialize option ROMs which support the Device Driver Initialization Model (DDIM).
Option ROMs which follow this model make the most efficient use of space consumed by option
ROMs. Refer to Appendix B for more information on the DDIM.
3.5 ISA Option ROMs and Resource Mapping
Given the fact that add-in cards are encouraged to make all of their resource assignments flexible, there
arises an interesting issue for Option ROMs, in how does the Option ROM code "know" which resource
values to use to communicate with the card? There are several possible solutions to this problem, but the
one selected for Plug and Play Option ROMs is as follows.
When the Plug and Play Option ROM is initialized, it will be passed the CSN and Read Data Port. The
Option ROM can use this information to determine which resources were assigned to it. When the Option
ROM has determined this, it should then setup its entry vectors based upon the resource assignment. For
example, if an add-in SCSI controller has two possible I/O Port assignments, 300h and 310h, then it
should have two different entry vectors for INT 13h. Depending upon which base I/O address is assigned,
the Option ROM will setup the INT 13h vector to point to the proper entry vector. Thereafter, whenever
Plug and Play BIOS Specification 1.0A
Page 22
INT 13h is called, the Option ROM may make the assumption that the base I/O address is the one that
goes with that entry point.
3.6 Error Recovery: Returning to the Boot flow
In the current boot model for standard PC compatible systems, once the system BIOS turns control over to
the Initial Program Load (IPL) device's boot sector, there is no way for the boot sector to return control to
the system BIOS in the event that an OS loader is not present on the disk, or the IPL fails for some other
reason.
In the Plug and Play Boot model, an attempt is made to correct this. If at any time after control has been
turned over to the IPL device's boot sector either the boot sector or some other portion of the OS loader
determines that the IPL device is incapable of supporting the boot process, control may be returned to the
system BIOS (so that the system BIOS can attempt to boot off of a different IPL device) by issuing either
an INT 19h or an INT 18h. The BIOS will intercept this INT vector and attempt to continue the bootstrap
process.
Plug and Play BIOS Specification 1.0A
Page 23
4.0 Configuration Support ________________________
A Plug and Play system BIOS, in addition to providing a conflict free bootstrap process, also provides
services to the operating system to assist with resource management during runtime. These services focus
on extending Plug and Play support to non-Plug and Play systemboard devices and dynamic event
notification.
4.1 System Device Configuration List
The system device configuration list consists of nodes or data structures that identify the embedded
devices that are on the system. The embedded devices consist of systemboard components that provide the
base functionality for the system. This includes devices such as the Programmable Interrupt Controller
(PIC), the DMA Controller, System Timer, Keyboard Controller, Integrated Video Controller, Floppy
Controller, etc. The system device configuration list only provides information about the systemboard
devices and does not include nodes for devices plugged into an expansion bus. The system device
configuration list does not identify the peripherals that are attached to the embedded systemboard devices.
For instance, the system configuration list will identify an integrated fixed disk controller but will not
provide nodes for any fixed disk drives that might be attached to the controller. It is assumed that
peripherals will be identified by other software. The system BIOS provides an interface for system
software to access the information in the system configuration list through the BIOS functions that are
defined later in this document. The System Device Node data structure provides configuration
information about a single systemboard device. The information returned for each systemboard
component reported through the Plug and Play BIOS interface will follow the data structure format
specified for the System Device Node. The next subsection describes the System Device Node data
structure.
4.2 System Device Node Definition
The System Device Node is the structure that represents a single embedded systemboard device. The
elements that make up this structure provide information that describe the device and the system resources
that have been allocated to the device. This includes reporting the system resources that have typically
been reserved for standard PC compatible systemboard devices, such as I/O port addresses from 00h to
FFh. The information for alternative or possible resource configuration settings can be provided in the
System Device Node; however, it is not required. The various possible resource settings can also be
provided in a configuration file or an image of the configuration file, in ROM, supplied by the system
vendor. This configuration file would contain the necessary configuration information not contained in
the System Device Node, and can provide more information to the user about the specific devices. If the
configuration information is contained in both the System Device Node and in a configuration file, then
the system resources possibilities for the device that are specified in the configuration file should take
precedence over the information contained in the system device node. The following data structure
defines the required elements for the base System Device Node. Please refer to the Plug and Play ISA
Specification version 1.0A (Section 4.6) for the maximum resources that a device node can use.
Plug and Play BIOS Specification 1.0A
Field
Size of the device node
Device node number/handle
Device product identifier
Device type code
Device node attribute bit-field
Allocated resource configuration descriptor block
Possible resource configuration descriptor block
Compatible device identifiers
Page 24
Size
WORD
BYTE
DWORD
3 BYTES
WORD
VARIABLE
VARIABLE
VARIABLE
Size of Device Node:
This field contains the size, in bytes, of the device node.
Device node number:
The node number, or handle, is a unique identifier value assigned to the node by the system BIOS and is
used to access the node information through the BIOS interface.
Device product identifier:
This field is an EISA ID, which is a seven character ASCII representation of the product identifier
compressed into a 32-bit identifier. The seven character ID consists of a three character manufacturer
code, a three character hexadecimal product identifier, and a one character hexadecimal revision number.
For example, the third revision of the ABC device might have an uncompressed ID such as ABC1003.
The manufacturer code is a 3 uppercase character code that is compressed into 3 5-bit values as follows:
1. Find hex ASCII value for each letter
2. Subtract 40h from each ASCII value
3. Retain 5 least-significant bits for each letter by discarding upper 3-bits because they are always 0.
4. Compressed code = Concatenate 0 and the 3 5-bit values for the character.
The format of the compressed product identifier is as follows:
Byte
Description
0
Bit 7:
Reserved (0)
Bits 6-2: 1st character of the compressed manufacturer code
Bits 1-0: Upper 2 bits of the 2nd character of the compressed manufacturer code
1
Bits 7-5: Lower 3 bits of the 2nd character of the compressed manufacturer code.
Bits 4-0: 3rd character of the compressed manufacturer code.
(bit 4 is most significant)
2
Bits 7-4: 1st hexadecimal digit of the product number. (bit 7 is most significant)
Bits 3-0: 2nd hexadecimal digit of the product number. (bit 3 is most significant)
3
Bits 7-4: 3rd hexadecimal digit of the product number (bit 7 is most significant)
Bits 3-0: Hexadecimal digit for the revision number. (bit 3 is most significant)
Refer to the Device Identifier Reference Table & Device Type Code Table for a list of product identifiers.
This list includes generic Plug and Play device identifiers for the standard systemboard components. See
the References section of this document.
Device type code:
This field is used to specify the type or characteristics of the node in the configuration list. There are
many different kinds of controllers and devices and through the type field you can identify which kind of
component this node represents.
The Device Type code is broken down into three byte fields. The first byte in the Device Type Code
consists of a Base Type code which indicates the general device type. The second byte is the device SubType and its definition is dependent upon the Base Type code. The third byte defines the specific device
programming interface, IF. Type, based on the Base Class and Sub-Class.
Refer to the Device Identifier Reference Table & Device Type Code Table for a description of Device
Type Codes.
Device node attribute bit-field:
Plug and Play BIOS Specification 1.0A
Page 25
The device node attributes provide additional information about the state of the device and the capabilities
of the device. This bit-field is defined as follows:
bit 15-9: reserved (0)
bits 8:7 0:0=device can only be configured for next boot (static)
0:1=device can be configured at runtime (dynamically)
1:0=Reserved
1:1=device can only be configured at runtime (dynamically)
bit 6: 0=device is not a removable system device
1=device is a removable system device
bit 5: 0=device is not a docking station device
1=device is a docking station device
bit 4: 0=device is not capable of being primary Initial Program Load (IPL) device
1=device is capable of being primary IPL device
bit 3: 0=device is not capable of being primary input device
1=device is capable of being primary input device
bit 2: 0=device is not capable of being primary output device
1=device is capable of being primary output device
bit 1: 0=device is configurable
1=device is not configurable
bit 0: 0=device can be disabled
1=device cannot be disabled
Bit 0 specifies whether the device can be disabled or not. If the device is disabled, it is assumed that the
system resources that the device was using are available for use by other devices.
Bit 1 indicates that the device is configurable. This implies that the system device node provides the
resource requirements for the device in the Possible resource configuration descriptor block. If the
device node does not specify the resource requirements or the device does not have any alternate system
resource requirements, bit 1 must be set to indicate that the device is not configurable.
Bits 2-4 identify the capability of the device being designated as a boot device.
Bit 5 indicates that the device resides on a docking station or convenience base.
Bit 6 indicates that the device node represents a device that is removable on the base system unit, such as
a removable floppy drive.
Bits 8:7 use three of the four possible states to indicate if the device node can be configured dynamically,
configured statically only for next boot or configured dynamically only. The fourth state is reserved.
Allocated resource configuration descriptor block:
The allocated resource descriptor block describes the system resources allocated to this device. The format
of the data contained in this block follows the format defined in the Plug and Play ISA Specification
under the section labeled Plug and Play Resources. The resource data is provided as a series of data
structures with each of the resource data structures having a unique tag or identifier. These are the
resource descriptors which specifically describe the standard PC system resources, such as Memory, I/O
addresses, IRQs, and DMA channels.
Possible resource configuration descriptor block:
The alternative resource selections that a particular device can support can be obtained from the data
contained in this block. The format of the data in this block follows the same format as the allocated
resource descriptor block. Refer to the Plug and Play ISA Specification under the section labeled Plug
and Play Resources for a description of the data structures that make up the resource descriptor blocks.
These are the resource descriptors which specifically describe the standard PC system resources, such as
Memory, I/O addresses, IRQs, and DMA channels.
The information in this block can be used by the system BIOS and/or system software for selecting a
conflict free resource allocation for this device without user intervention. The data in this block is
optional. If this information is not provided in this structure, it can optionally be provided in a
configuration file for the systemboard that defines the configuration information for the embedded
devices. If the possible resource configurations are not specified in either place the device is assumed to
Plug and Play BIOS Specification 1.0A
Page 26
be a static device, which means it is not configurable. If the information is provided in this descriptor
block and in a configuration file, the possible resource selections must be specified in the same order that
they are described in the configuration file. If the node does not contain the alternative resource selections
then the first byte in this block will contain the End Tag descriptor, which is described in Plug and Play
ISA Specification, to indicate that there are no resources in this block.
Compatible device identifiers:
The compatible device identifiers block specifies the IDs of other devices that this device is compatible
with. System software can use this information to load compatible device drivers if necessary. The format
of the data contained in this block follows the format defined in the Plug and Play ISA Specification
under the section labeled Plug and Play Resources - Compatible Device ID.
4.3 Plug and Play BIOS Functions
The following subsections describe the Plug and Play BIOS interface. The function return values are
listed in Appendix C. The Plug and Play BIOS functions will preserve all FLAGS and registers
except for the AX register, which will contain the return code. The BIOS functions will use the
caller's stack and a minimum of 1024 bytes of stack space must be available to these functions. It is
important to note that system BIOS function(s) used to set the configuration of a systemboard device
will not validate the configuration information passed by the caller and may not return an error
code.
Option ROM initialization routines can not depend on any of the Plug and Play runtime functions to be
available until after INT19 has been invoked at the end of the POST process.
4.4 Plug and Play Installation Check
This section describes the method for system software to determine if the system has a Plug and Play
BIOS. This Plug and Play installation check indicates whether the system BIOS support for accessing the
configuration information about the devices on the systemboard is present and the entry point to these
BIOS functions. This method involves searching for a signature of the ASCII string $PnP in system
memory starting from F0000h to FFFFFh at every 16 byte boundary. This signature indicates the system
may have aPlug and Play BIOS and identifies the start of a structure that specifies the entry point of the
BIOS code which implements the support described in this document. The system software can determine
if the structure is valid by performing a Checksum operation.
The method for calculating the checksum is to add up Length bytes from the top of the structure, including
the Checksum field, into an 8-bit value. A resulting sum of zero indicates a valid checksum operation.
The entry points specified in this structure are the software interface to the BIOS functions. The structure
element that specifies the 16-bit protected mode entry point will allow the caller to construct a protected
mode selector for calling this support. The structure of the Plug and Play BIOS Support Installation
Check is as follows:
Field
Offset
Length
Value
Signature
00h
4 BYTES
$PnP (ASCII)
Version
04h
BYTE
10h
Length
05h
BYTE
21h
Control field
06h
WORD
Varies
Checksum
08h
BYTE
Varies
Event notification flag address
09h
DWORD
Varies
Real Mode 16-bit offset to entry point
0Dh
WORD
Varies
Real Mode 16-bit code segment address
0Fh
WORD
Varies
16-Bit Protected Mode offset to entry point
11h
WORD
Varies
16-Bit Protected Mode code segment base
13h
DWORD
Varies
address
Plug and Play BIOS Specification 1.0A
OEM Device Identifier
Real Mode 16-bit data segment address
16-Bit Protected Mode data segment base address
Page 27
17h
1Bh
1Dh
DWORD
WORD
DWORD
Varies
Varies
Varies
Signature is represented as the ASCII string "$PnP", where byte 0='$' (24h), byte 1='P' (50h),byte 2='n'
(6Eh), and byte 3='P' (50h).
Version - This is a BCD value that implies a level of compliance with major (high nibble) and minor (low
nibble) version changes of the Plug and Play BIOS specification. For example, the BCD value 10h would
be interpreted as version 1.0.
Length - Length of the entire Installation Structure expressed in bytes. The length count starts at the
Signature field.
The Control field is a bit-field that provides system capabilities information.
bits 15:2: Reserved (0)
bits 1:0: Event notification mechanism
00=Event notification is not supported
01=Event notification is handled through polling
10=Event notification is asynchronous (at interrupt time)
Checksum - The method for calculating the checksum is to add up the number of bytes in the Installation
Structure, including the Checksum field, into an 8-bit value. A resulting sum of zero indicates a valid
checksum.
The Event notification flag address specifies the physical address of the Event Flag if event notification
is handled through polling. When event notification is handled through polling, bit 0 of the Event Flag
will be set when a system event occurs. System software will monitor or poll the Event Flag for
notification of an event.
If events are handled through asynchronous notification, the system BIOS will specify a system device
node which can be obtained from the Get Node runtime function. The system device node for
asynchronous event management will be identified through the device identifier field in the device node
data structure and will specify the IRQ number and an I/O port address. This event system device node
can be defined in one of two ways. First, the device node can follow the generic implementation in which
the device identifier is PNP0C03, and the interrupt number and I/O address assigned are system specific.
The only requirement with the generic implementation is that the I/O address bit used for detecting the
source of the interrupt and clearing the interrupt line is bit 0. If bit 0 of this I/O address is set to 1, then
the interrupt was generated due to a system event. The interrupt service routine should reset the interrupt
line by clearing bit 0 at the specified I/O address. All other bits read from the I/O address should not be
modified. The second way the event system device node can be defined is implementation specific where
the system vendor must supply their own device identifier and whatever resources are required for
servicing the event interrupt. This method will require a specific device driver associated with the device
node identifier to support the event notification interface.
System software should check the Control field to determine the event notification method implemented
on the system.
Refer to the Event Notification Interface section for more information on events.
The Real Mode 16-Bit interface is basically the segment:offset of the entry point.
The 16-Bit Protected Mode interface specifies the code segment base address so that the caller can
construct the descriptor from this segment base address before calling this support from protected mode.
The offset value is the offset of the entry point. It is assumed that the 16-Bit Protected Mode interface is
sufficient for 32-Bit Protected Mode callers.
The caller must also construct data descriptors for the functions that return information in the function
arguments that are pointers. The only limitation is that the pointer offset can only point to the first 64K
bytes of a segment.
If a call is made to these BIOS functions from 32-bit Protected Mode, the 32-bit stack will be used for
passing any stack arguments to the Plug and Play BIOS functions. However, it is important to note that
the Plug and Play BIOS functions are not implemented as a full 32-bit protected mode interface and will
Plug and Play BIOS Specification 1.0A
Page 28
access arguments on the stack as a 16-bit stack frame. Therefore, the caller must ensure that the function
arguments are pushed onto the stack as 16-bit values and not 32-bit values. The stack parameter passing
is illustrated in Figure 4.4.1 below.
Figure 4.4.1 - 16-bit Stack Frame on 32-bit Stack
The Plug and Play system BIOS can determine whether the stack is a 32-bit stack or a 16-bit stack in 16bit and 32-bit environments through the use of the LAR - Load Access Rights Byte Instruction. The LAR
instruction will load the high order doubleword for the specified descriptor. By loading the access rights
for the current stack segment selector, the system BIOS can check the B-bit (Big bit) of the stack segment
descriptor which identifies the stack segment descriptor as either a 16-bit segment (B-bit clear) or a 32-bit
segment (B-bit set).
In addition to executing the LAR command to get the entry point stack size, the BIOS code should avoid
ADD BP,X type stack operands in runtime service code paths. These operands carry the risk of faulting if
the 32-bit stack base happens to be close to the 64K boundary. For the 16-Bit Protected Mode interface, it
is assumed that the segment limit fields will be set to 64K. The code segment must be readable. The
current I/O permission bit map must allow accesses to the I/O ports that the system BIOS may need access
to in order to perform the function. The current privilege level (CPL) must be less than or equal to I/O
privilege level. This will allow the Plug and Play BIOS to use sensitive instructions such as CLI and STI.
The OEM Device Identifier field provides a means for specifying a device identifier for the system. The
format of the OEM Device Identifier follows the format specified for EISA product identifiers. A system
identifier is not required and if not specified, this field should be 0.
The entry point is assumed to have a function prototype of the form,
int FAR (*entryPoint)(int Function, ...);
and follow the standard 'C' calling conventions.
System software will interface with all of the functions described in this specification by making a far call
to this entry point. As noted above, the caller will pass a function number and a set of arguments based on
the function being called. Each function will also include an argument which specifies a data selector
which will allow the Plug and Play BIOS to access and update variables within the system BIOS memory
space. This data selector parameter is required for protected mode callers. The caller must create a data
segment descriptor using the 16-bit Protected Mode data segment base address specified in the Plug and
Play Installation Structure, a limit of 64KB, and the descriptor must be read/write capable. Real mode
callers are required to set this parameter to the Real Mode 16-bit data segment address specified in the
Plug and Play Installation Structure.
Any functions described by this specification which are not supported should return the
FUNCTION_NOT_SUPPORTED return code. The function return codes are described in Appendix C of
this specification.
4.4.1 System BIOS Plug and Play Compliance - "$PnP"
This section describes the support that is guaranteed by the "$PnP" string in the Plug and Play Installation
Check structure and specifies the BIOS support required to be Plug and Play compliant for systems with
different characteristics. A Plug and Play compliant system will guarantee:
Plug and Play BIOS Specification 1.0A
Page 29
1. The Plug and Play Structure is valid.
2. Any calls made to the Plug and Play BIOS functions will either perform the function as
described by Version 1.0 of this specification or return the FUNCTION_NOT_SUPPORTED error
code. Plug and Play compliant systems are required to provide the support as outlined in the table
below.
3. All of the runtime Plug and Play services will be contained in a contiguous 64K code segment.
Presence of the $PnP structure in the system BIOS does not mean that the system is fully Plug and Play
compliant. For instance, a system BIOS could have a valid $PnP structure; yet, return
FUNCTION_NOT_SUPPORTED for each of the functions described in this specification. The following
table specifies the required Plug and Play BIOS support necessary for systems with different
characteristics to meet full Plug and Play compliance.
System Characteristics
Required Functions
Optional Functions
Systems with embedded devices on the systemboard.
00h, 01h, 02h
Proprietary bus devices or local ISA devices on the
systemboard.
Systems that support docking to expansion bases
03h, 04h, 05h
Reserved
06h, 07h, 08h
Systems with an ISA expansion bus
40h
09h, 0Ah
ESCD Interface Functions
41h, 42h, 43h
Systems supporting APM 1.1 (and greater)
0Bh
*Note:
Functions 09h, 0Ah, and 40h are designed to support systems with an ISA Expansion bus. The
information which must be stored in nonvolatile media is the information concerning the resources
allocated to static legacy ISA devices. If functions 09h and 0Ah designate that the system implementation
utilizes the ESCD for storing static resource allocation, then the caller should utilize the interface defined
by the ESCD Specification to report statically allocated resources. Functions 41h, 42h, and 43h defined in
section 4.7 specify the ESCD interface. Refer to the ESCD Specification for a complete description of the
interfaces to support the ESCD as well as the format of the ESCD. BIOS support of these functions is
optional.Systems with an ISA Expansion bus may provide these BIOS functions to enhance the Plug and
Play BIOS POST process for assigning a conflict free configuration to the required boot devices.
The following table provides some examples of systems with certain characteristics and categorically lists
the functions that would be required to be Plug and Play compliant.
Plug and Play BIOS Specification 1.0A
Page 30
Example Systems
Runtime
Services
Event
Systems without an ISA bus;
limited or a variety of boot devices;
No Dynamic Events
Systems without an ISA bus;
limited or a variety of boot devices;
Dynamic Events supported
Systems with an ISA bus;
No Dynamic Events
Systems with an ISA bus;
Dynamic Events supported
Required
Not
Required
Required
Required
Required
ISA
Allocated
Resource
Support
Not
Required
ISA PnP
Isolation
Required
Not
Required
Not
Required
Not
Required
Required
Not
Required
Not
Required
Required
Not
Required
Required
4.5 System Configuration Interface
The functions described in the following subsections define the System Configuration Interface for
obtaining information about the systemboard devices and for setting the system resources utilized by the
configurable devices.
Plug and Play BIOS Specification 1.0A
Page 31
4.5.1 Function 0 - Get Number of System Device Nodes
Synopsis:
int FAR (*entryPoint)(Function, NumNodes, NodeSize, BiosSelector);
int Function;
/* PnP BIOS Function 0 */
unsigned char FAR *NumNodes;
/* Number of nodes the BIOS will return */
unsigned int FAR *NodeSize;
/* Size of the largest device node */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Required. This function will return the number of nodes that the system BIOS will return information for
in NumNodes. These nodes represent only the systemboard devices. In addition to the number of nodes,
the system BIOS will return the size, in bytes, of the largest System Device Node in NodeSize. This
information can be utilized by the system software to determine the amount of memory required to get all
of the System Device Nodes.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode, the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64KB, and the descriptor must
be read/write capable. If this function is called from real mode, BiosSelector should be set to the Real
Mode 16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
The function is available in real mode and 16-bit protected mode.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred - error code (The function return codes are described in
Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
push
push
push
push
push
push
call
add
cmp
jne
.
.
.
Bios Selector
segment/selector of NodeSize
offset of NodeSize
segment/selector of NumNodes
offset of NumNodes
GET_NUM_NODES
FAR PTR entryPoint
sp,12
ax,SUCCESS
error
.
.
; pointer to NodeSize
; pointer to NumNodes
; Function 0
; Clean up stack
; Function completed successfully?
; No-handle error condition
4.5.2 Function 1 - Get System Device Node
Synopsis:
int FAR (*entryPoint)(Function, Node, devNodeBuffer, Control, BiosSelector);
int Function;
/* PnP BIOS Function 1 */
unsigned char FAR *Node;
/* Node number/handle to retrieve */
struct DEV_NODE FAR *devNodeBuffer;
/* Buffer to copy device node data to */
Plug and Play BIOS Specification 1.0A
unsigned int Control;
unsigned int BiosSelector;
Page 32
/* Control Flag */
/* PnP BIOS readable/writable selector */
Description:
Required. This function will copy the information for the specified System Device Node into the buffer
specified by the caller. The Node argument is a pointer to the unique node number (handle). If Node
contains 0, the system BIOS will return the first System Device Node. The devNodeBuffer argument
contains the pointer to the caller's memory buffer. On return, Node will be updated with the next node
number, or if there are no more nodes, it will contain FFh. The System Device Node data will be placed
in the specified memory buffer.
The Control flag provides a mechanism for allowing the system software to request a node that indicates
either how the specified systemboard device is currently configured or how it is configured for the next
boot. Control is defined as:
Bits 15:2: Reserved (0)
Bit 1: 0=Do not get the information for how the device will be configured for the next boot.
1=Get the device configuration for the next boot (static configuration).
Bit 0: 0=Do not get the information for how the device is configured right now.
1=Get the information for how the device is configured right now.
If Control flag is 0, neither bit 0 nor bit 1 is set, or if both bits are set, this function should return
BAD_PARAMETER.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode, the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64KB, and the descriptor must
be read/write capable. If this function is called from real mode, BiosSelector should be set to the Real
Mode 16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
The function is available in real mode and 16-bit protected mode.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred - error code (The function return codes are described in
Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
push
push
push
push
push
push
push
call
add
cmp
jne
.
.
.
Bios Selector
Control Flag
segment/selector of devNodeBuffer
offset of devNodeBuffer
segment/selector of Node
offset of Node
GET_DEVICE_NODE
FAR PTR entryPoint
sp,14
ax,SUCCESS
error
.
.
.
; pointer to devNodeBuffer
; pointer to Node number
; Function 1
; Clean up stack
; Function completed successfully?
; No-handle error condition
Plug and Play BIOS Specification 1.0A
Page 33
4.5.3 Function 2 - Set System Device Node
Synopsis:
int FAR (*entryPoint)(Function, Node, devNodeBuffer, Control, BiosSelector);
int Function;
/* PnP BIOS Function 2 */
unsigned char Node;
/* Node number/handle to set */
struct DEV_NODE FAR *devNodeBuffer;
/* Buffer containing device node data */
unsigned int Control;
/* Control Flag */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Required. This function will allow system software to set the system resource configuration for the
specified System Device Node. The Node argument will contain the unique node number (handle) for the
device that is to be set, and devNodeBuffer contains the pointer to the node data structure that specifies the
new resource allocation request. The node data structure must completely describe the resource settings
for the device. A node data structure that contains partial settings will result in the improper set up of the
device. It cannot be assumed that any previous resource allocations will remain when this call is made.
It is important to note that the resource descriptors that define the resource allocation must be specified in
the same order as listed in the allocated resource configuration block for the system device node to be set.
The allocated resource configuration block should be used as a template for setting the new resources for
the device to ensure that the descriptors are specified in the correct format. In fact, the devNodeBuffer can
be a copy of the fetched System Device Node with its allocated resource configuration block modified to
reflect the desired new device configuration. Therefore, this function must be implemented to extract and
use only the relevant new resource configuration information while ignoring all other extraneous node
information. This function will not validate the resource settings or the checksum passed by the caller,
and may not return an error code.
To disable a device, all resource descriptors in the allocated resource configuration block of the System
Device Node must be set to zero. The resource attribute information field and the tag field are "Don't
Care" and may be zeroed.
The Control flag provides a mechanism for allowing the system software to indicate whether the
systemboard device configuration specified by this call is to take affect immediately or at the next boot.
Control is defined as:
Bits 15:2: Reserved (0)
Bit 1: 0=Do not set the device configuration for the next boot.
1=Set the device configuration for the next boot (static configuration).
Bit 0: 0=Do not set the device configuration dynamically.
1=Set the device configuration right now (dynamic configuration).
If Control flag is 0, neither bit 0 nor bit 1 is set and this function should return BAD_PARAMETER. If
both bits are set, then the system BIOS will attempt to set the configuration of the device right now
(dynamic configuration), as well as set the device configuration for the next boot (static configuration).
When both bits are set, it is possible that the NOT_SET_STATICALLY warning could be generated.
This indicates that the device was configured dynamically, but could not be configured statically (See
Appendix C, Error Codes).
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64k, and the descriptor must be
read/write capable. If this function is called from real mode, BiosSelector should be set to the Real Mode
16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
The function is available in real mode and 16-bit protected mode.
Returns:
Plug and Play BIOS Specification 1.0A
Page 34
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred - error code (The function return codes are described in
Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
push
push
push
push
push
push
call
add
cmp
jne
.
.
.
Bios Selector
Control
segment/selector of devNodeBuffer
offset of devNodeBuffer
Node
SET_DEVICE_NODE
FAR PTR entryPoint
sp,12
ax,SUCCESS
error
.
.
.
; Control flag
; pointer to devNodeBuffer
; node number - only low 8-bits used
; Function 2
; Clean up stack
; Function completed successfully?
; No-handle error condition
4.6 Event Notification Interface
Certain classes of systems may provide the capability for the addition or removal of system devices while
the system unit is powered on, such as inserting a Notebook unit into a Docking Station. System BIOS
support is necessary for providing Event Notification accessible to system software so that when devices
are added or removed the system software will comprehend the use or release of system resources by those
devices. Event Notification can be implemented as either a polled method or as asynchronous events.
System software can check the Control Word, which is located in the BIOS Plug and Play Header
structure, to determine the Event Notification method supported on the system. Refer to the Plug and
Play Installation Check section for more information on the BIOS Plug and Play Header and the Control
Word. The Control Word has bits defined that indicate the type of Event Notification. The BIOS Plug
and Play Header structure also contains the Event notification flag address, which specifies the physical
location of the Event Flag for polling. The Event Flag is the event polling location. When a system event
occurs bit 0 of the Event Flag will be set to indicate a pending event. Therefore, if the method for Event
Notification is through polling, system software should monitor the Event Flag to determine when a
configuration event has occurred.
The asynchronous method of Event Notification allows system software to install an interrupt handler as a
means for notification. The system BIOS will specify a system device node, which can be obtained from
the Get Node runtime function, that will specify the requirements for handling asynchronous events. The
system device node for asynchronous event management will be identified through the device identifier
field in the device node data structure, and will specify the interrupt number and an I/O port address.
This event system device node can be defined in one of two ways. First, the device node can follow the
generic implementation in which the device identifier is PNP0C03 and the interrupt number and I/O
address assigned are system specific. The only requirement with the generic implementation is that the
I/O address bit used for detecting the source of the interrupt and clearing the interrupt line is bit 0. If bit 0
of this I/O address is set to 1, then the interrupt was generated due to a system event. The interrupt
service routine should reset the interrupt line by clearing bit 0 at the specified I/O address. All other bits
read from the I/O address should not be modified. The second way the event system device node can be
defined is implementation specific where the system vendor must supply their own device identifier and
whatever resources are required for servicing the event interrupt. This method will require a specific
device driver associated with the device node identifier to support the event notification interface.
Plug and Play BIOS Specification 1.0A
Page 35
When the system software is notified of an event by either mechanism, it can then call the BIOS runtime
function to get the event which will return a message specifying the type of event. These events are
specific to the system and do not represent events that can occur on the various expansion busses, such as
PCMCIA insertion and removal events. The following table describes the types of events that are reported
through this BIOS interface:
Plug and Play BIOS Specification 1.0A
Page 36
Event Identifier
ABOUT_TO_CHANGE_CONFIG
Value
0001h
DOCK_CHANGED
0002h
SYSTEM_DEVICE_CHANGED
0003h
CONFIG_CHANGE_FAILED
0004h
UNKNOWN_SYSTEM_EVENT
FFFFh
OEM_DEFINED_EVENTS
8000h
thru
FFFEh
Description
This message provides the system with a mechanism whereby
system software can obtain notification from the system BIOS
when a change is about to be made to the system. This
notification encompasses initiating a docking, or undocking,
sequence. For systems that support this message, the docking
sequence will be suspended until the system software issues a
Send_Message() to the system BIOS with either an OK
message indicating that it's OK to dock/undock the system, or an
ABORT message that signals the BIOS to halt the event. (Refer
to Send Message function description below for more
information.)
This message indicates that new devices have either been
successfully added or removed from the system, such as docking
to, or undocking from, a docking station. This message will be
used to indicate that a convenience base has been
added/removed from the system.
This message indicates that removable ("pluggable") system
devices have been removed or inserted into the base unit.
This message indicates that the system detected an error when
attempting to add or remove devices to/from the system, such as
attempting to dock to the docking station, or failing to
successfully undock from the docking station. An error code will
be returned in the return status for the Get_Event Plug and Play
BIOS function if the system is able to determine the cause of the
CONFIG_CHANGE_FAILED. Appendix C contains a complete
list of return codes.
An unknown system event has occurred. The system BIOS is not
able to determine the type of event.
OEM defined events allow OEM to define events specific to
their system implementation. These events are only
comprehended by the OEM. These events are identified by the
upper bit of the event message being set (bit 7=1).
To properly support event management, a PnP BIOS should implement the PNP_OS_ACTIVE and
PNP_OS_INACTIVE messages, as well as their associated event timing requirements and PnP-OS-Active
states as described in section 4.6.2.
Plug and Play BIOS Specification 1.0A
Page 37
4.6.1 Function 3 - Get Event
Synopsis:
int FAR (*entryPoint)(Function, Message, BiosSelector);
int Function;
/* PnP BIOS Function 3 */
unsigned int FAR *Message;
/* Storage for the event message */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Required for Dynamic Event Management. This function will allow system software to retrieve a message
specifying the type of event that has occurred on the system. This function is supported for either event
notification by polling or for asynchronous event notification, if the system BIOS provides event
notification. It is the responsibility of this function to clear the event flag when called if the event
notification method implemented is through polling.
If a system event has occurred this call will return the appropriate event notification message in the
memory location specified by the Message argument. Message will be set to one of the following event
notification messages:
ABOUT_TO_CHANGE_CONFIG
DOCK_CHANGED
SYSTEM_DEVICE_CHANGED
CONFIG_CHANGE_FAILED
UNKNOWN_SYSTEM_EVENT
OEM_DEFINED_EVENT
The event notification messages are defined in the table at the start of Event Notification Interface section.
If Message is CONFIG_CHANGE_FAILED and the system is able to determine the cause of the error,
then the appropriate error should be returned in AX. This will allow system software the ability notify the
user of the cause of the failure. Refer to Appendix C for a description of the error codes associated with
the CONFIG_CHANGE_FAILED event message.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64k, and the descriptor must be
read/write capable. If this function is called from real mode, BiosSelector should be set to the Real Mode
16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
This function is available in real mode and 16-bit protected mode.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred or no pending events - error code (The function return
codes are described in Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Plug and Play BIOS Specification 1.0A
Page 38
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
.
push
push
push
push
call
add
cmp
jne
.
.
Bios Selector
segment/selector of Message
offset of Message
GET_EVENT
FAR PTR entryPoint
sp,8
ax,SUCCESS
error
.
.
.
; pointer to Message
; Function 3
; Clean up stack
; Function completed successfully?
; No-handle error condition
4.6.2 Function 4 - Send Message
Synopsis:
int FAR (*entryPoint)(Function, Message, BiosSelector);
int Function;
/* PnP BIOS Function 4 */
unsigned int Message;
/* Docking Message */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Required for Dynamic Event Management. This function will provide system software with a mechanism
for interacting with the system while handling system events. There are three classes of messages that are
supported by this interface: Response Messages, Control Messages, and OEM Defined Messages. The
Response Messages are used as a means whereby the system BIOS will not proceed with a particular event
until the system software provides a response instructing the system BIOS to continue or abort the
processing of that event. Message values 0 through 3Fh are reserved for Response Messages. Control
Messages provide system software with the ability to cause a particular event to happen. Message values
40h through 7Fh are reserved for Control Messages. OEM Defined Messages are specific to the OEM's
system implementations and are only understood by the OEM. Message values 8000h through FFFFh
identify OEM Defined Messages. The following table describes the event messages that system software
can send to the system BIOS, where Message has one of the following meanings:
Plug and Play BIOS Specification 1.0A
Page 39
Response Messages 00h through 3Fh:
Message Identifier
OK
ABORT
Control Messages 40h through 7Fh:
Message Identifier
UNDOCK_DEFAULT_ACTION
Value
00h
01h
Value
40h
POWER_OFF
41h
PNP_OS_ACTIVE
42h
PNP_OS_INACTIVE
43h
OEM Defined Messages 8000h through FFFFh:
Message Identifier
Value
Description
Instructs the system to continue with the sequence which
initiated the event. This message is only valid when the Get
Event function has returned one of the ABOUT_TO_XXXXX
events. When the system software is notified with an
ABOUT_TO_XXXXX message, the appropriate actions will not
take place until the Send Message BIOS Function is called with
OK.
Abort the action which initiated the ABOUT_TO_XXXXX
event. This message instructs the system BIOS to prevent the
event from occurring. For instance, if the event is an undocking
sequence, then the system will not be allowed to undock. It is
assumed that it is the responsibility of the system software to
communicate to the user the reason for not allowing the system
to carry out the action for the event. This message is only valid
when Get Event has returned one of the ABOUT_TO_XXXXX
messages.
Description
This message provides a mechanism for system software to soft
eject the system and instructs the system BIOS to take the
default action when ejecting the system.
This message instructs the system BIOS to power off the system.
It is assumed that the system software will perform the necessary
actions to shut the system down before sending this message.
This message allows the PnP BIOS to track whether a PnP OS is
active and defines event timing. The PnP BIOS may default to
either a PnP-OS-Inactive or PnP-OS-Active state as needed.
However, upon initial OS load, a PnP OS will register with the
PnP BIOS by sending the PNP_OS_ACTIVE message to the PnP
BIOS. When the PNP_OS_ACTIVE message is received, the
PnP BIOS will operate in the PnP-OS-Active state. In this state,
the PnP BIOS will wait forever after signaling a system event.
This will allow the PnP OS to execute a Plug and Play BIOS
Function Get Event call and handle the event (See Section 4.6).
Although a PnP BIOS is not required to support the
PNP_OS_ACTIVE message, support is recommended in systems
that generate events. If this message is unsupported, then
MESSAGE_NOT _SUPPORTED should be returned.
This message complements the PNP_OS_ACTIVE message. A
PnP OS will send the PNP_OS_INACTIVE message to the PnP
BIOS upon OS termination. When the PNP_OS_INACTIVE
message is received, the PnP BIOS will operate in the PnP-OSInactive state. In this state, no PnP event timing constraints
exist. The PnP BIOS does not have to wait for the PnP OS to
execute a Plug and Play BIOS Function Get Event call (See
Section 4.6) and can handle event timing in the manner it best
determines. Although a PnP BIOS is not required to support the
PNP_OS_INACTIVE message, support is recommended in
systems that generate events. If this message is unsupported,
then MESSAGE_NOT _SUPPORTED should be returned.
Description
Plug and Play BIOS Specification 1.0A
OEM_DEFINED_MESSAGES
Page 40
8000h
thru
FFFFh
This message allows OEMs to define messages specific to their
system implementation. These messages are only comprehended
by the OEM. These messages are identified by the upper bit of
the message.
If the system BIOS does not support one of the specified messages, this function will return
MESSAGE_NOT_SUPPORTED.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode, the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64KB, and the descriptor must
be read/write capable. If this function is called from real mode, BiosSelector should be set to the Real
Mode 16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
This function is available in real mode and 16-bit protected mode.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred - error code (The function return codes are described in
Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
.
push
push
push
call
add
cmp
jne
.
.
Bios Selector
Message
SEND_MSG
FAR PTR entryPoint
sp,6
ax,SUCCESS
error
.
.
.
; Message
; Function 4
; Clean up stack
; Function completed successfully?
; No-handle error condition
Plug and Play BIOS Specification 1.0A
Page 41
4.6.3 Function 5 - Get Docking Station Information
Synopsis:
int FAR (*entryPoint)(Function, DockingStationInfo, BiosSelector);
int Function;
/* PnP BIOS Function 5 */
unsigned char FAR *DockingStationInfo;
/* Pointer to docking station info structure */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Required for Dynamic Event Management. This function will allow system software to get information
which specifies the type of docking device, either expansion or convenience base, the system is connected
to, as well as the capabilities of the docking device. The docking station information will be returned in
the memory buffer pointed to by DockingStationInfo in the following format:
Field
Offset
Length
Value
Docking station location identifier
00h
DWORD
Varies
Serial number
04h
DWORD
Varies
Capabilities
08h
WORD
Varies
Docking station location identifier:
This field is the docking device location identifier. The identifier should follow the EISA device
identifier format. The docking device location identifier will allow system software to
differentiate between the types of docking stations and convenience bases that the base system
unit can be connected to. This enables the system software to better determine the various
docked and undocked configuration states. LocationId will be set to
UNKNOWN_DOCKING_IDENTIFIER (0xFFFFFFFF) for docking stations and/or convenience
bases that do not have a product identifier.
Serial number:
SerialNum is not required; however, if the docking station does not have a serial number, then 0
should be returned in this parameter.
Capabilities:
The Docking Capabilities bit field is defined as follows:
Bits 15:3 Reserved (0)
Bit 2:1 - 00=System should be powered off to dock or undock (Cold Docking)
01=System supports Warm Docking/Undocking, system must be in suspend
10=System supports Hot Docking/Undocking, not required to be in suspend
11=Reserved
Bit 0 - 0=Docking station does not provide support for controlling the
docking/undocking sequence (Surprise Style).
1=Docking station provides support for controlling the docking/undocking
sequence (VCR Style).
If the system supports docking and is unable to determine the docking station capabilities, this function
will return UNABLE_TO_DETERMINE_DOCK_CAPABILITIES. All other relevant information, such
as the docking station identifier, will be returned in the data structure.
If the system does not support docking, this function will return FUNCTION_NOT_SUPPORTED. If the
system supports docking, but is not currently docked, this function will return SYSTEM_NOT_DOCKED
and will not return any information about a docking station.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode, the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64KB, and the descriptor must
be read/write capable If this function is called from real mode, BiosSelector should be set to the Real
Mode 16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
Plug and Play BIOS Specification 1.0A
Page 42
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
The function is available in real mode and 16-bit protected mode.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred or the system is not currently docked (The function return
codes are described in Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
push
push
push
push
call
add
cmp
jne
.
.
.
Bios Selector
segment/selector of DockingStationInfo
offset of DockingStationInfo
GET_DOCK_INFO
FAR PTR entryPoint
sp,8
ax,SUCCESS
error
.
.
; pointer to docking station info data structure
; Function 5
; Clean up stack
; Function completed successfully?
; No-handle error condition
Plug and Play BIOS Specification 1.0A
4.6.4 Function 6 - Reserved
This function has been reserved for future implementations and should return
FUNCTION_NOT_SUPPORTED.
4.6.5 Function 7 - Reserved
This function has been reserved for future implementations and should return
FUNCTION_NOT_SUPPORTED.
4.6.6 Function 8 - Reserved
This function has been reserved for future implementations and should return
FUNCTION_NOT_SUPPORTED.
Page 43
Plug and Play BIOS Specification 1.0A
Page 44
4.7 Extended Configuration Services
This section describes the optional extended services provided by the System BIOS on Plug and Play
platforms.
The extended configuration services are a mechanism whereby the system software may specify the system
resources assigned to devices that have been installed in the system. This information will be maintained
by the BIOS in some form of nonvolatile storage. Depending upon the amount of nonvolatile storage
available to store system configuration information, one can either store detailed configuration
information for all devices or limit the information to a description of the summary resource usage by the
static ISA devices in the system. In both cases, this information is to help the BIOS configure boot
devices during the Power On Self Test (POST) phase. See Section 2.1.4 in the system POST area for a
more complete description of the POST process.
Get & Set Statically Allocated Resources
Functions 9 and Ah allow the OS to effectively reserve resources allocated by legacy cards in a system.
This provides a resource usage map for the BIOS to use to avoid resource conflicts when allocating
resources to other devices. Only summary resource usage information by the legacy ISA cards must be
stored in nonvolatile storage. This information describes the cumulative usage of system resources by all
legacy ISA cards but does not identify the specific resources used by each card. The POST configuration
software will use this information to avoid resource conflicts when configuring boot devices. This
solution can be implemented with minimum NVRAM; however, it does afford less control over the
configuration. The example in section 4.7.1 describes how Plug and Play ISA resource descriptor
information can be stored compactly. The storage structure definition is left completely up to the OEM.
The operating system should call function 9 to determine if the platform Plug and Play interface supports
the ISA resource descriptors or not. If this call returns without an error, it can be assumed that the
platform is storing the ISA resource descriptor information in a proprietary bit map format. If function
calls 9 or 0Ah return the USE_ESCD_SUPPORT error message, then the caller can assume that this
platform supports the ESCD method of data storage.
Read & Write Extended System Configuration Data (ESCD)
The ESCD data storage method allows OEMs to differentiate a platform with additional Plug and Play
features. Since the data format stores information about which devices are using what resources, it is
possible to maintain an image of the Last Working Configuration of all know devices. Additionally,
system software can modify the ESCD at runtime and affect the configuration of devices for the next boot.
This allows bootable devices to be enabled/disabled and other devices to be locked into specific
configurations. The ESCD also provides detailed configuration information about static devices allowing
the POST configuration software to avoid conflicts with these cards. In general, the ESCD allows the
Plug and Play system BIOS to more fully configure the system at power up; this is important for
platforms that must support non-Plug and Play operating systems.
The ESCD format describes every device in the system so storage requirements are much larger. A
typical platform requires 2-4KB of NVRAM. The Plug and Play interface can support a function call
that allows the caller to Get NVRAM size attributes, and it supports two other functions that provide
Read/Write access to the Extended System Configuration Data where it is stored in the NVRAM.
The operating system should call function 9 to determine which data storage format this platform's Plug
and Play interface supports. If the function 9 call returns without an error, it can be assumed that the
platform is storing the ISA resource descriptor information in a proprietary bit map format. If function
calls 9 or 0Ah return the USE_ESCD_SUPPORT error message, then the caller can assume that this
platform supports the ESCD method of data storage.
More detailed and current information about the ESCD definition and format specification can be found
in the ESCD Specification.
Plug and Play BIOS Specification 1.0A
Page 45
4.7.1 Function 9 - Set Statically Allocated Resource Information
Synopsis:
int FAR (*entryPoint)(Function, ResourceBlock, BiosSelector);
int Function;
/* PnP BIOS Function 9 */
unsigned char FAR *ResourceBlock;
/* Block of statically allocated resources */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Optional. This function will allow system software to report the system resources that are being utilized
by the static ISA devices installed in the system. The system software must pass a complete list of system
resources used by ALL of the legacy ISA devices that are not located on the system board. Therefore, any
time a legacy ISA device is added or removed from the system, the system software must construct a new
resource map and pass the information to the system BIOS by making this function call. This information
is important to the Plug and Play BIOS POST functionality for achieving the ability to bootstrap the
operating system from a Plug and Play boot device by allowing the Plug and Play BIOS to configure the
boot device around the legacy ISA devices. The resources allocated to the legacy ISA devices in the
system are reported in the ResourceBlock parameter. The format of the data contained in the block
follows the format defined in the Plug and Play ISA Specification under the section labeled Plug and Play
Resources. This data is provided as a series of data structures with each structure having a unique tag or
identifier. The resource descriptors supported by this function are the descriptors that describe IRQ,
DMA, I/O addresses, and memory resources. The resource information specified in this block must be
terminated with an END_TAG resource descriptor.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode, the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64KB, and the descriptor must
be read/write capable. If this function is called from real mode, BiosSelector should be set to the Real
Mode 16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
If this function returns USE_ESCD_SUPPORT, then reporting resources allocated to devices to the
system BIOS must be handled through the interface defined by the ESCD Specification (see sections 4.7.4
- 4.7.6, functions 41h, 42h and 43h.).
This function is available in real mode and 16-bit protected mode.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred or no pending events - error code (The function return
codes are described in Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
.
push
push
push
push
call
add
cmp
jne
.
.
Bios Selector
segment/selector of the Resource Block
; Pointer to the data structure of isa
offset of Resource Block
SET_STATICALLY_ALLOCATED_RESOURCES
; Function 9
FAR PTR entryPoint
sp,8
; Clean up stack
ax,SUCCESS
; Function completed successfully?
error
; No-handle error condition
.
resources
Plug and Play BIOS Specification 1.0A
Page 46
.
.
A BIOS implementor is only required to follow the interface described by this function. The format of the
data passed by the system software must follow the Plug and Play ISA resource descriptor definition. How
the statically allocated resource information is actually stored is left up to the BIOS implementor. An
example of how the information could be stored more compactly than the Plug and Play ISA resource
descriptors is as follows:
IRQ
2 Bytes - Bits set indicate IRQ used by unconfigurable ISA device
DMA 1 Byte - Bits set indicate DMA used by unconfigurable ISA device
I/O
24 Bytes - Bits set indicate I/O addresses used (100h-3ffh). Assumes 4 ports used per
I/O address bit set
Memory 640k to 1Mg
3 Bytes - Represented in 16k blocks
Memory 1Mg to 16Mg
2 Bytes - Represented in 1Mg increments.
Storing the information this way would allow the system resources used by unconfigurable ISA devices to
be contained in 32 bytes.
Note: this is only an example. It is completely up to the BIOS vendor to choose an appropriate format
for storing the data, which means it could possibly be stored in less than 32 bytes or require more than
32 bytes.
Plug and Play BIOS Specification 1.0A
Page 47
4.7.2 Function 0Ah - Get Statically Allocated Resource Information
Synopsis:
int FAR (*entryPoint)(Function, ResourceBlock, BiosSelector);
int Function;
/* PnP BIOS Function 0Ah */
unsigned char FAR *ResourceBlock;
/* Block of resources statically allocated to devices */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Optional. This function will return the system resources that are being utilized by the legacy ISA devices
that are installed in the system. These system resources are the resources that have been reported to the
system BIOS through the Set Allocated ISA Resource Info function. The resources allocated to the legacy
ISA devices in the system are reported in the ResourceBlock parameter. It is important to note that the
information returned represents the resource usage rounded up to the nearest granularity range supported
by the system BIOS and not the actual resources used by the legacy ISA devices in the system. It is
recommended that the system software keep track of the system resources used by legacy ISA cards in
order to account for the exact system resources usage of the legacy ISA cards installed in the system. The
format of the data contained in the block follows the format defined in the Plug and Play ISA
Specification under the section labeled Plug and Play Resources. This data is provided as a series of data
structures with each structure having a unique tag or identifier. The ResourceBlock must be a minimum
of 2 Kbytes to ensure that there is adequate space for the system BIOS to return the legacy ISA resource
information.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64k, and the descriptor must be
read/write capable. If this function is called from real mode, BiosSelector should be set to the Real Mode
16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
If this function returns USE_ESCD_SUPPORT, then accessing the information describing the resources
allocated to devices to the system BIOS must be handled through the interface defined by the ESCD
Specification. Refer to the ESCD Specification for a complete description of the interfaces to support the
ESCD as well as the format of the ESCD.
This function is available in real mode and 16-bit protected mode.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred or no pending events - error code (The function return
codes are described in Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Plug and Play BIOS Specification 1.0A
Page 48
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
.
push
Bios Selector
push
segment/selector of the Resource Block
; Pointer to the data struct of isa resources
push
offset of Resource Block
push
GET_STATICALLY_ALLOCATED_RESOURCES
; Function 0Ah
call
FAR PTR entryPoint
add
sp,8
; Clean up stack
cmp
ax,SUCCESS
; Function completed successfully?
jne
error
; No-handle error condition
.
4.7.3 Function 40h - Get Plug & Play ISA Configuration Structure
Synopsis:
int FAR (*entryPoint)(Function, Configuration, BiosSelector);
int Function;
/* PnP BIOS Function 40h */
unsigned char FAR *Configuration;
/* Address of caller's config. structure buffer*/
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Required. This function is used to get the Plug and Play ISA Configuration structure. The Plug and Play
ISA Configuration data structure contains configuration information specific to ISA Plug and Play
support. This function will copy the data structure to the caller's memory buffer specified by
Configuration. A system without any ISA bus capabilities will return the
FUNCTION_NOT_SUPPORTED error code. When the ISA bus is present, the fields in this data
structure will be set with the appropriate values. If the system BIOS did not identify any Plug and Play
ISA cards in the system during POST, then the Total number of Card Select Numbers field will be zero
and the value in the ISA Read Data Port field is invalid and must not be used by system software.
On systems with a dynamic ISA bus, like portables, function 40h will be more flexible. When an ISA bus
is present, the information returned by function 40h will always be valid after a cold boot. On a cold boot
with no ISA bus present, function 40h will return zeros. After an ISA warm/hot dock, the function 40h
information will also be valid, if the plug and play BIOS isolates and enumerates the plug and play
adapter cards before returning control to the plug and play operating system. If the BIOS does not reenumerate after an ISA warm/hot dock event, then the information returned by function 40h will be zeros.
After an ISA undock event, this information will also be zeros.
The format of the Plug and Play ISA Configuration structure is defined as follows:
Field
Offset
Length
Value
Structure Revision
00h
BYTE
01
Total number of Card Select Numbers (CSNs) 01h
BYTE
Varies
assigned
ISA Read Data Port
02h
WORD
Varies
Reserved
04h
WORD
0
Structure Revision:
This is an ordinal value that indicates the revision number of this structure only and does not imply a level
of compliance with the Plug and Play BIOS version.
Total number of Card Select Numbers:
This field specifies the total number of CSNs assigned to ISA Plug and Play cards by the system BIOS
during the Power-On Self Test (POST).
Plug and Play BIOS Specification 1.0A
Page 49
ISA Read Data Port:
The ISA Read Data Port is used to read information from the Plug and Play registers. The value
represented here is the I/O port that was determined by the system BIOS to not conflict with another ISA
I/O port. Refer to the ISA Plug and Play Specification for more information on the ISA Read Data Port.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode, the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
specified in the Plug and Play Installation Check data structure, a limit of 64KB, and the descriptor must
be read/write capable. If this function is called from real mode, BiosSelector should be set to the Real
Mode 16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
This function is available in real mode and 16-bit protected mode.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred - error code (The function return codes are described in
Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
push
Bios Selector
push
segment/selector of Config. structure buffer ; pointer to configuration data buffer
push
offset of Configuration structure buffer
push
GET_ISA_CONFIG_STRUC
; Function 40h
call
FAR PTR entryPoint
add
sp,8
; Clean up stack
cmp
ax,SUCCESS
; Function completed successfully?
jne
error
; No-handle error condition
.
.
4.7.4 Function 41h - Get Extended System Configuration Data (ESCD) Info
Synopsis:
int FAR (*entryPoint)(Function, MinESCDWriteSize, ESCDSize, NVStorageBase,
BiosSelector);
int Function;
/* PnP BIOS Function 041h */
unsiged int FAR *MinESCDWriteSize;
unsigned int FAR *ESCDSize;
unsigned long FAR *NVStorageBase;
unsigned int BiosSelector;
/* Minimum buffer size in bytes for writing to NVS */
/* Size allocated for the ESCD... */
/* ...within the nonvolatile storage block */
/* 32-bit physical base address for.*/
/* .mem mapped nonvolatile storage media */
/* PnP BIOS readable/writable selector */
Description:
Optional. This function provides information about the nonvolatile storage on the system that contains
the Extended System Configuration Data (ESCD). It returns the size, in bytes, of the minimum buffer
required for writing to NVS in MinESCDWriteSize, the maximum size, in bytes, of the block within the
nonvolatile storage area allocated specifically to the ESCD in ESCDSize, and if the nonvolatile storage is
memory mapped, the 32-bit absolute physical base address will be returned in NVStorageBase. The
physical base address of the memory mapped nonvolatile storage will allow the caller to construct a 16-bit
Plug and Play BIOS Specification 1.0A
Page 50
data segment descriptor with a limit of 64K and read/write access. This will enable the Plug and Play
system BIOS to read and write the memory mapped nonvolatile storage in a protected mode environment.
If the nonvolatile storage is not memory mapped the value returned in NVStorageBase should be 0. It is
assumed that the size of the nonvolatile storage that contains the ESCD will not exceed 32K bytes.
Refer to the ESCD Specification for a complete description of the interfaces to support the ESCD as well
as the format of the ESCD.
4.7.5 Function 42h - Read Extended System Configuration Data (ESCD)
Synopsis:
int FAR (*entryPoint)(Function, ESCDBuffer, ESCDSelector, BiosSelector)
int Function;
/* PnP BIOS Function 042h */
char FAR *ESCDBuffer;
/* Addr of caller's buffer for storing ESCD */
unsigned int ESCDSelector;
/* ESCD readable/writable selector */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Optional. This function is used to read the ESCD data from nonvolatile storage on the system into the
buffer specified by ESCDBuffer. The entire ESCD will be placed into the buffer. It is the responsibility of
the caller to ensure that the buffer is large enough to store the entire ESCD. The caller should use the
output from Function 41 (the ESCDSize field) when calculating the size of the ESCDBuffer. The system
BIOS will return the entire ESCD, including information about system board devices. The system board
device configuration information will be contained in the slot 0 portion of the ESCD. The caller can
determine the size of the data in the ESCD from the ESCD Configuration Header Structure. In protected
mode, the ESCDSelector has base = NVStorageBase and limit of at least NVStorageSize. In real mode, the
ESCDSelector is a segment that points to NVStorageBase.
Refer to the ESCD Specification for a complete description of the interfaces to support the ESCD as well
as the format of the ESCD.
4.7.6 Function 43h - Write Extended System Configuration Data (ESCD)
Synopsis:
int FAR (*entryPoint)(Function, ESCDBuffer, ESCDSelector, BiosSelector);
int Function;
/* PnP BIOS Function 043h */
char FAR *ESCDBuffer;
/* Buffer containing complete ESCD to write... */
/* ...to nonvolatile storage */
unsigned int ESCDSelector;
/* ESCD readable/writable selector */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Optional. This function will write the Extended Static Configuration Data (ESCD) contained in the
ESCDBuffer to nonvolatile storage on the system. The data contained in the caller's buffer must contain a
complete block of ESCD structures describing the configuration information for devices on the system.
The caller should use the output from Function 41 (the MinESCDWriteSize field) when calculating the
size of the ESCDBuffer. The system BIOS can determine the size of the data in the ESCD structure from
the ESCD Configuration Header Structure within the caller's ESCD buffer.
Refer to the ESCD Specification for a complete description of the interfaces to support the ESCD as well
as the format of the ESCD.
Plug and Play BIOS Specification 1.0A
Page 51
4.8 Power Management Services
The following subsections describe the Plug and Play support for allowing interaction with Advanced
Power Management (APM) 1.1 and greater.
4.8.1 Function 0Bh - Get APM ID Table
Synopsis:
int FAR (*entryPoint)(Function, Bufsize, ApmIdTable, BiosSelector);
int Function;
/* PnP BIOS Function 0Bh */
unsigned int FAR *BufSize;
/* Size of buffer to copy APM ID table to */
unsigned char FAR *ApmIdTable;
/* Address of caller's buffer for the table */
unsigned int BiosSelector;
/* PnP BIOS readable/writable selector */
Description:
Required for Power Management. This function will copy the table of APM 1.1 (or greater) device
identifier to Plug and Play device identifier mappings to the buffer specified by the caller. This allows the
operating system to use the APM interface to perform power management on individual devices controlled
by the system BIOS. If BufSize indicates that the buffer is not large enough to contain the entire table, the
system BIOS will return BUFFER_TOO_SMALL and the size of the buffer required to contain the entire
table will be returned in the caller's BufSize parameter. Therefore, the caller can call this function with
BufSize equal to 0 to determine the size of the buffer it needs to allocate for the APM identifier table. The
apmIDTable argument contains the pointer to the caller's memory buffer. If the buffer is large enough, on
return apmIDTable will contain the APM identifier table. Each entry in the table will be specified in the
following format:
Field
Length
Value
Device identifier
DWORD
Varies
APM 1.1 identifier (version 1.1 or greater)
WORD
Varies
Device Identifier:
This field is the Plug and Play device identifier. The Logical Device ID provides a
mechanism for uniquely identifying multiple logical devices embedded in a single physical
board. The format of the logical device ID is composed of three character compressed ASCII
EISA ID and a manufacturer specific device code.
APM identifier:
This element specifies the corresponding APM device identifier.
An APM identifier table with multiple entries would be described as follows:
Field
Device identifier #1
APM identifier #1
Device identifier #2
APM identifier #2
:
:
Device identifier #n
APM identifier #n
This call supports APM version 1.1 or greater. The APM interface INT 2Fh supports a get version call.
The BiosSelector parameter enables the system BIOS, if necessary, to update system variables that are
contained in the system BIOS memory space. If this function is called from protected mode the caller
must create a data segment descriptor using the 16-bit Protected Mode data segment base address
Plug and Play BIOS Specification 1.0A
Page 52
specified in the Plug and Play Installation Check data structure, a limit of 64K, and the descriptor must be
read/write capable. If this function is called from real mode, BiosSelector should be set to the Real Mode
16-bit data segment address as specified in the Plug and Play Installation Check structure. Refer to
section 4.4 above for more information on the Plug and Play Installation Check Structure and the
elements that make up the structure.
This function is available in real mode and 16-bit protected mode.
Example scenario: An operating system provides a device driver level-interface to both the Plug and Play
BIOS as well as the APM 1.1 (or greater) interface. An OEM or third party wishes to write a Plug and
Play device driver for a device built into the system in order to provide enhancements available through
operating-system services. However, he also wishes to power manage the device using support already
available in the machine's APM 1.1 implementation. This function provides a means for the device driver
to determine which Plug and Play identifiers have corresponding power management support through an
APM 1.1 device identifier.
Returns:
0 if successful - SUCCESS
!0 if an error (Bit 7 set) or a warning occurred - error code (The function return codes are described in
Appendix C)
The FLAGS and registers will be preserved, except for AX which contains the return code.
Example:
The following example illustrates how the 'C' style call interface could be made from an assembly
language module:
push
push
push
push
push
push
call
add
cmp
jne
.
.
.
Bios Selector
segment/selector of APM Id table
offset of APM Id table
segment/selector of table buffer size
offset of APM Id table buffer size
GET_APM_TABLE
FAR PTR entryPoint
sp,12
ax,SUCCESS
error
.
.
.
; pointer to APM Id table buffer
; pointer to APM Id table buffer size
; Function 0Bh
; Clean up stack
; Function completed successfully?
; No-handle error condition
Plug and Play BIOS Specification 1.0A
Page 53
Appendix A: Generic Option ROM Headers__________
Generic Option ROM Header expansion
(Offsets are all based from the beginning of the Header)
Offset
Length
Value
Description
0h
DWORD
$??? (ASCII)
Signature
04h
BYTE
Varies
Structure Revision
05h
BYTE
Varies
Length (in 16 byte increments)
06h
WORD
Varies
Offset of next Header (0000 if none)
08h
BYTE
0FFFFh
Reserved
09h
BYTE
Varies
Checksum
10h
Varies
Varies
Specific Header Type Data
Generic
Generic
Generic
Generic
Generic
Generic
Specific
Signature - All Expansion Headers will contain a unique expansion header identifier. Each different
Expansion Header will have its own unique signature. Software that wishes to make use of any given
Expansion Header simply traverses the linked list of Generic Expansion Headers until the Expansion
Header with the desired signature is found, or the end of the list is encountered.
Example: The Plug and Play expansion header's identifier is the ASCII string "$PnP" or hex 24 50 6E
50h.
Structure Revision - This is an ordinal value that indicates the revision number of this structure only and
does not imply a level of compliance with the Plug and Play BIOS version.
Length - Length of the entire Expansion Header expressed in sixteen byte blocks. The length count starts
at the Signature field.
Offset of Next Header - This location contains a link to then next expansion ROM header in this Option
ROM. If there are no other expansion ROM headers then this field will have a value of 0h.
Reserved - Reserved for Expansion
Checksum - Each Expansion Header is checksummed individually. This allows the software that wishes
to make use of an expansion header the ability to determine if the expansion header is valid.
The system software can determine if the expansion header is valid by performing a Checksum operation.
The method for validating the checksum is to add up Length bytes, including the Checksum field, into an
8-bit value. A resulting sum of zero indicates a valid checksum operation.
Specific Header data - This area is used by the specific device header and is defined uniquely for each
Expansion Header.
Plug and Play BIOS Specification 1.0A
Page 54
Appendix B: Device Driver Initialization Model_______
Please Note: The Device Driver Initialization Model (DDIM) is provided as an extension of the current
option ROM model. Current bus devices cannot be guaranteed that the systems in which they are
installed will support DDIM. Therefore, current bus device Option ROMs (ISA, EISA, MCA, PCMCIA)
must support the standard initialization model, and may optionally support the DDIM. The Option ROM
may determine if it is being initialized using a DDIM by attempting to write to, and read back from his
data space. If the Option ROM can successfully write to its data space, then it should support a DDIM
initialization. Otherwise, it must perform a standard initialization.
As of this writing, the PCI architecture is the only architecture wherein Option ROMs are guaranteed
support for DDIM.
In an effort to reduce the amount of UMB (Upper Memory Block) space consumed by add-in Option
ROMs, and to more efficiently use the available UMB space, Plug and Play Option ROMs should support
the Device Driver Initialization Model (DDIM).
Under this model, all Option ROMs installed in a Plug and Play system which indicate that they support
DDIM will be copied into RAM by the System BIOS. The System BIOS will then execute a FAR CALL
into the device's initialization vector.
Devices which support DDIM may then initialize themselves, update their RAM image with static Data (if
necessary), and then discard the initialization code, by updating the length byte at offset 3h and
recalculating their checksum. The System BIOS will then initialize the next DDIM ROM by copying it to
RAM on the next 2 KB boundary following the end of the most recently initialized DDIM ROM (or in the
next available UMB which is large enough to contain both the Runtime and Initialization code of the
DDIM ROM).
Once all DDIM Option ROMs have been initialized, the System BIOS will Write Protect the RAM images
and proceed with the boot process.
Flow:
System BIOS copies the DDIM Option ROM Copy to RAM
System BIOS executes a FAR CALL to Initialization Vector
Option ROM initializes the device
Option ROM updates any static data structures
Option ROM updates the ROM Length and Check sum
Option ROM returns to the System BIOS with Return Status
System BIOS Write Protects RAM image of ROM.
Advantages:
* Provides more efficient use of Upper Memory Blocks. Initialization code may be discarded.
* Provides a seamless mechanism whereby Option ROMs may be copied to RAM
* Provides Option ROMs with a means of storing Static Data Structures built at boot time.
* Allows board vendors to use lower performance ROM devices (on buses that are guaranteed to support
this architecture - PCI).
Plug and Play BIOS Specification 1.0A
Page 55
Appendix C: Return Codes _______________________
The following table represents the return codes for the BIOS functions.
Bit 7 set indicates an error has occurred.
Success Codes 00h:
Return Code
SUCCESS
Value
00h
Description
Function completed successfully
Warning Codes 01h through 7Fh:
Return Code
Reserved
NOT_SET_STATICALLY
Value
01h
7Fh
Description
Error Codes 81h through FFh:
Return Code
UNKNOWN_FUNCTION
FUNCTION_NOT_SUPPORTED
INVALID_HANDLE
Value
81h
82h
83h
BAD_PARAMETER
84h
SET_FAILED
EVENTS_NOT_PENDING
SYSTEM_NOT_DOCKED
NO_ISA_PNP_CARDS
85h
86h
87h
88h
UNABLE_TO_DETERMINE_DOCK_
CAPABILITIES
CONFIG_CHANGE_FAILED_NO_
BATTERY
CONFIG_CHANGE_FAILED_
RESOURCE_CONFLICT
89h
BUFFER_TOO_SMALL
8Ch
USE_ESCD_SUPPORT
8Dh
MESSAGE_NOT_SUPPORTED
8Eh
8Ah
8Bh
Warning that indicates a device could not be
configured statically, but was successfully configured
dynamically. This return code is used only when
function 02h is requested to set a device both
statically and dynamically.
Description
Unknown, or invalid, function number passed
The function is not supported on this system.
Device node number/handle passed is invalid or out
of range.
Function detected invalid resource descriptors or
resource descriptors were specified out of order.
Set Device Node function failed.
There are no events pending.
The system is currently not docked.
Indicates that no ISA Plug and Play cards are
installed in the system.
Indicates that the system was not able to determine
the capabilities of the docking station.
The system failed the undocking sequence because it
detected that the system unit did not have a battery.
The system failed to successfully dock because it
detected a resource conflict with one of the primary
boot devices; such as Input, Output, or the IPL
device.
The memory buffer passed in by the caller was not
large enough to hold the data to be returned by the
system BIOS.
This return code is used by functions 09h and 0Ah to
instruct the caller that reporting resources explicitly
assigned to devices in the system to the system BIOS
must be handled through the interfaces defined by the
ESCD Specification.
This return code indicates the message passed to the
system BIOS through function 04h, Send Message, is
not supported on the system.
Plug and Play BIOS Specification 1.0A
HARDWARE_ERROR
Page 56
8Fh
This return code indicates that the system BIOS
detected a hardware failure.
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