Datasheet

Intel
®
Xeon
®
Processor C5500/C3500 Series
February 2010 Datasheet, Volume 1
Order Number: 323103-001 41
Interfaces
2.1.3.5 Mirrored Channel Mode
The following modes of operation are required to implement mirroring.
2.1.3.5.1 Mirroring Redundant Mode
Software puts the Integrated Memory Controller into this mode whenever the memory
image in both channels is identical, or where they differ, the contents are not valid. In
addition, both WDBs must be empty before enabling this mode.
The final step in mirroring is to inform the channels that they are now redundant, so
that they stop signaling uncorrectable errors when they fail. After the mirroring setup is
complete, the state of the mirrored channels can be changed from active to redundant.
It is not critical to minimize the time between changing each channel to redundant
state. No inconsistency results if one channel is in redundant state and the other is not
when a failure occurs. If the non-redundant channel fails, it is fatal. If the redundant
channel fails, it will transfer operation to the non-redundant channel. In this mode, the
Integrated Memory Controller duplicates writes to both channels.
Reads are sent to one channel or the other, as described in the channel mapper.
Uncorrectable errors in this mode are logged and signaled as correctable, but change
the channel state to Disabled, and the working partner to Redundancy Loss.
The BIOS follows this sequence to set up mirroring mode:
channel active
•init done
mem init
mirror enable
channel map
•smi enable
•mem config hide
2.1.3.5.2 Disabled Channel Operation
After an uncorrectable error, the logical channel disables itself. However, to support
continued operation, the logical channel must complete handshakes for any requests it
receives. No more channel errors will be logged. The channel behaves as if the result is
correct.
The failed channel resets its columns in the channel mapper so that all subsequent
requests are routed to the working partner. The coupling of channels for credit return
must be removed. Write credits will be returned as soon as the working partner
provides them.
2.1.3.5.3 Redundancy Loss Mode
The Integrated Memory Controller changes the state of the working channel to
redundancy loss when its partner fails.
The failed channel clears its bits in the channel mapper, so that all accesses will be
directed to the working channel. The working channel will enter redundancy loss state.
The failed channel will enter disabled state.
If any uncorrectable errors on the working channel are detected in the same clock or
later than the uncorrectable error that caused the loss of redundancy, then they must
be signaled as uncorrectable. This requires that error signaling be delayed long enough