Plug and Play BIOS Specification

Plug and Play BIOS Specification 1.0A Page 20
Field Size
Size of the device node WORD
Device node number/handle BYTE
Device product identifier DWORD
Device type code 3 BYTES
Device node attribute bit-field WORD
Allocated resource configuration descriptor block VARIABLE
Possible resource configuration descriptor block -
should only specify the END_TAG resource
descriptor
2 BYTES
Compatible device identifiers 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).