Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
863
SMBus Interface Unit—Intel
®
81341 and 81342
14.3.1
SMBus Controller
The 81341 and 81342 SMBus slave port interfaces to the configuration spaces of each
ATU function, and also interfaces to the memory-mapped registers. This gives SM
(server management) visibility into configuration space registers in the 81341 and
81342 ATUs 81341 and 81342.
14.3.1.1 SMBus Commands
The 81341 and 81342 supports six SMBus commands:
Sequencing these commands initiates internal accesses to 81341 and 81342
configuration and memory-mapped registers. For high reliability, 81341 and 81342 also
supports the optional Packet Error Checking feature (CRC-8) and is enabled or disabled
with each transaction.
Every configuration and memory read or write first consists of an SMBus write
sequence which initializes the Bus Number, Device, function number, memory address
offset etc. The term sequence is used since these variables can be initialized by the
SMBus master with a single block write or multiple word or byte writes. The last write in
the sequence that completes the initialization performs the internal configuration/
memory read or write. The SMBus master can then initiate a read sequence which
returns the status of the internal read or write command and also the data in case of a
read.
Each SMBus transaction has an 8-bit command driven by the master. The command
encodes the following information:
• Block Write
• Word Write
• Byte Write
• Block Read
• Word Read
• Bytes Read
Table 546. SMBus Command Encoding
Bit
Description
7
Begin: The Begin bit when set indicates the first transaction of the read or write sequence.
6
End: The End bit when set indicates the last transaction of the read or write sequence.
5
Memory/Configure: Indicate whether memory or configuration space is being accesses in this SMBus
sequence. Value of ‘1’ indicates memory and a value of ‘0’ indicate configuration.
4
PEC Enable: Indicates that PEC is enabled when set. When set, each transaction in the sequence ends
with an extra CRC byte. 81341 and 81342 would check for CRC on writes and generate CRC on reads.
3:2
Internal Command:
00 — Read DWord
01 — Write Byte
10 — Write Word
11 — Write Dword
All access are naturally aligned to the access width. This field specifies the internal command to be
issued by the SMBus slave logic to the 81341 and 81342
1:0
SMBus command:
00 — Byte
01 — Word
10 — Block
11 — Reserved
This field specifies the SMBus command to be issued on the SMBus. This field is used as an indication
of the length of transfer so that the slave knows when to expect the PEC packet (when enabled).