Intel Extensible Firmware Interface, Specification

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Device Path Protocol
Version 1.02 12/12/00 133
5.3.6 BIOS Boot Specification Device Path
This Device Path is used to describe the booting of non-EFI-aware operating systems. This Device
Path is based on the IPL and BCV table entry data structures defined in Appendix A of the
BIOS
Boot Specification . The BIOS Boot Specification Device Path defines a complete Device Path and
is not used with other Device Path entries. This Device Path is only needed to enable platform
firmware to select a legacy non-EFI OS as a boot option.
Table 5-27. BIOS Boot Specification Device Path
Mnemonic
Byte
Offset Byte
Length
Description
Type 0 1 Type 5 – BIOS Boot Specification Device Path.
Sub-Type 1 1 Sub-Type 1 – BIOS Boot Specification Version 1.01.
Length 2 2 Length of this structure in bytes. Length is 8 + n bytes.
Device Type 4 2 Device Type as defined by the BIOS Boot Specification.
Status Flag 6 2 Status Flags as defined by the BIOS Boot Specification
Description String 8 n ASCIIZ string that describes the boot device to a user. The
length of this string
n can be determined by subtracting 8
from the Length entry.
Example BIOS Boot Specification Device Types would include:
•
00h = Reserved
•
01h = Floppy
•
02h = Hard Disk
•
03h = CD-ROM
•
04h = PCMCIA
•
05h = USB
•
06h = Embedded network
•
07h..7Fh = Reserved
•
80h = BEV device
•
81h..FEh = Reserved
•
FFh = Unknown
5.4 Device Path Generation Rules
5.4.1 Housekeeping Rules
The Device Path is a set of Device Path nodes. The Device Path must be terminated by an End of
Device Path node with a sub-type of End the Entire Device Path. A NULL Device Path consists of
a single End Device Path Node. A Device Path that contains a NULL pointer and no Device Path
structures is illegal.
All Device Path nodes start with the generic Device Path structure. Unknown Device Path types
can be skipped when parsing the Device Path since the length field can be used to find the next