Plug and Play BIOS Specification

Plug and Play BIOS Specification 1.0A Page 9
• 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.