The Dmi Header; Verifying The Dmi Information Structure - HP Vectra VL5 4 Technical Reference Manual

5 Read off the required values.
Each type of table has a pre-defined format. For a list of the major table types, refer to
"DMI Sub-Structure Tables," in this chapter.
6 Use the pointer to retrieve string values.
All string values are terminated by a null (zero) value.

THE DMI HEADER

The DMI header is the starting point for all DMI information.
Field
DMI Header Signature
Version
DMI Header Length
Pointer to DMI structures
Length of DMI structures
Checksum of DMI structures
Checksum of DMI header

VERIFYING THE DMI INFORMATION STRUCTURE

Before accessing the DMI tables, the checksums must be verified to ensure the reliability of the
information. To calculate a checksum value of a structure, do the following steps:
1 Add together all the bytes of the structure.
2 Convert the value to negative.
3 Cast the value to a byte (take the low byte).
There are two checksums, one for the DMI header and another for the remaining DMI structure.
To verify these two checksums, do the following steps:
1 Locate the DMI header.
2 Using the length value of the DMI header, calculate the checksum value for the DMI
header. (When adding together the bytes of the header, exclude the checksum byte, offset
0Dh.)
3 Verify this value against the checksum given for the DMI header.
4 Retrieve the position and length of the DMI structures.
5 Calculate the checksum value for the DMI structures.
6 Verify this value against the checksum given for the DMI structures.
Offset Length
0h 4 bytes
4h 1 byte
5h 1 byte
0Ah 4 bytes (DWORD)
0Ch 2 bytes (WORD)
0Ch 1 byte
0Dh 1 byte
Value
"$DMI"
00010010 (Ver 1.2)
0Eh
Far pointer (variable)
variable
variable
variable