Appendix A¶

Checksum Calculation¶

Checksum ranges are noted throughout this specification. These are provided as a range of bytes to include within the checksum calculation. These are not provided as a range for the resultant checksum value.

Steps for calculating checksums:

Set checksum value to zero (0).
Perform a byte-wise sum of all other bytes within the specified range.
Subtract byte-wise sum from step 2 from zero (0).
Assign value from step 3 to checksum.

Checksum ranges that include the checksum itself assume a value of zero or do not include the checksum in the range at all. Padded ranges might include the pads. This does not affect the outcome of the checksum calculation since the pad values themselves are required to be 0x00.

Type/Length Byte Format¶

The following table presents the specification for the type/length byte format as detailed in IPMI Specification v2.0, at section 13 of the document.

Table: Type/Length Format

Bits	Meaning
7:6	Type code
00…	Binary or unspecified
01…	Binary-coded decimal plus
10…	6-bit ASCII packed (overrides language codes)
11…	Interpretation depends on language codes. 11b indicates 8-bit ASCII + Latin 1 if the language code is English for the area or record containing the field, or 2-byte UNICODE (least significant byte first) if the language code is not English. At least two bytes of data must be present when this type is used. Therefore, the length (number of data bytes) will always be >1 if data is present, 0 if data is not present.
5:0	Number of data bytes 000000 indicates that the field is empty. When the type code is 11b, a length of 000001 indicates ‘end of fields, i.e., Type/Length = C1h indicates end of fields.

ASCII+LATIN1 is derived from the first 256 characters of unicode 2.0. The first 256 codes of unicode follow ISO 646 (ASCII) and ISO 8859/1 (Latin 1). The Unicode C0 Controls and Basic Latin set defines the first 128 8-bit characters (00h-7Fh), and the C1 Controls and Latin-1 Supplement defines the second 128 (80h-FFh).

6-bit ASCII is the 64 characters starting from character 20h (space) from the ASCII+LATIN1 set. For example, 6- bit ASCII value 000000b maps to 20h (space), 000001b maps to 21h (!), etc..,

Packed 6-bit ASCII takes the 6-bit characters and packs four characters to every three bytes, with the first character in the least significant six bits of the first byte.

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