Intel
®
81341 and 81342—SMBus Interface Unit
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
874
Order Number: 315037-002US
14.3.4
Error Handling
The SMBus slave interface handles two types of errors: internal address error and PEC.
Internal address errors can occur, for example, when the SMBus request on the 81341
and 81342 internal bus fails due to an address parity error. This error manifests itself
as a Not-Acknowledge (NACK) for the read or write command (End bit is set). Other
internal errors include the read or write command receiving a master or target abort on
the internal interface. When the master receives a NACK, the entire transaction should
be reattempted.
When the master supports packet error checking (PEC) and the PEC enable bit in the
command is set, then the PEC byte is checked in the slave interface. When the check
indicates a failure, then the slave NACKs the PEC packet and does not issue the
command on the internal interface.
An SMBus master must either do PEC on all transactions in a sequence or not do it at
all; that is, it cannot turn on PEC in the middle of a sequence.
A PEC error in the middle of a sequence must be re-started from the beginning of the
sequence; that is, the begin bit set.
14.3.5
SMBus Interface Reset
The master in two ways can reset the slave interface state machine in 81341 and
81342:
The master holds
SMBCLK
low for 25 ms cumulative. Cumulative in this case means
that all the “low time” for
SMBCLK
is counted between the Start and Stop bit. When
this totals 25 ms before reaching the Stop bit, the interface is reset.
The master holds
SMBCLK
continuously high for 50 ms.
Besides these, the SMBus interface in 81341 and 81342 is also reset on a P_RST#,
WARM_RST# or an in-band warm reset from PCI Express*.