Peripheral component interconnect (PCI) clock jitter might cause unpredictable result - IBM eServer xSeries 380

Resolving The Problem

Source

RETAIN tip H174441

Symptom

The IBM xSeries 380 Peripheral component interconnect (PCI) clock jitter might cause an unpredictable result such as:

• System hangs
• Blue screens

Affected configurations 

The system might be any of the xSeries 380, type 8683, any models.
 
The system is configured with one or more (1-4) processors.

Solution

There will be no definitive solution for this issue. A specification update will be made to document the behavior.
 
Workaround

Option 1
Operate the PCI bus at 33MHz
The basic input/output system (BIOS) release 1.2 or higher contains a setup option to force the PCI buses connected to each bridge chip to 33MHz (PCI slots 3-5, 6-8, 9+10).
 
The referenced file is available from the following URL: http://www.ibm.com/systems/support
 
Option 2
Running adapters at 66MHz
Populate only a single bus connected to each PCI wide expansion bus (WXB). If the bus is populated with 66MHz adapters only, then the other (sister) bus must be left unpopulated. (See table.)
 
The PCI configuration is made up of seven PCI buses across ten PCI slots. The PCI expansion bridge (PXB) is not affected. The other six buses are configured in pairs, with each pair connected to a single WXB component.
 
The buses behind the 3-WXBs are capable of running at 33MHz or 66MHz.

 
NOTE: The onboard SCSI device shares the PCI bus with slot 3. This onboard SCSI device operates at 66MHz, which results in this PCI bus operating at 66MHZ. Therefore, if slot 3 is populated with a 66MHz adapter, no adapters can populate slots 4 and 5.
 
Here are some configurations that will not produce the problem (It does not contain all possible configurations.):

• With a single 66MHZ adapter, up to nine (9) adapters, can be installed (the 66MHz adapter in slot-10, and eight (8) 33MHz adapters in slots 1-8, with the onboard SCSI running at 33MHZ)
• With two 66MHZ adapters, up to nine (9) adapters, can be installed (the 66MHz adapters in slots 6+7, and seven (7) 33MHz adapters in slots 1-5, 9 and 10 - with the onboard SCSI running at 33MHz)
• With three 66MHz adapters, up to eight (8) adapters can be installed (the 66MHz adapters in slots 6, 7 and 9, and five (5) 33MHz adapters in slots 1-5, with the onboard SCSI running at 33MHz)

The maximum number of 66MHz adapters that can be installed without the possibility of jitter being seen is four (4).
(Populate slots 3, 6, 7 and 9, or slots 3, 6, 7 and 10.)

NOTE: 33MHz adapters can be installed in slots 1 and 2 in the configuration.
 
Additional information

This behavior has only been seen in a test environment. In some cases, adapters have not been affected; in other cases, the adapters report parity error, master abort, PCI system error, or nothing at all. It might result in system hangs or blue screens.