Processor reorder buffer timeout - a debug guide

by Ai Bee Lim & Jack R. Johnson, Intel Corp. , TechOnline India - October 13, 2010

This paper provides an overview of the processor reorder buffer timeout and provides methodology to debug these types of system issues. Using the debug methods and debug tools suggested in this document should help reduce the time to debug these system issues.

This paper provides an overview of the processor reorder buffer timeout and provides methodology to debug these types of system issues. Using the debug methods and debug tools suggested in this document should help reduce the time to debug these system issues. The process is to gather more information about the failure until the cause is identified and then put preventive steps in place to eliminate the failure.

Processor reorder buffer (ROB) timeout is not new, yet debug engineers often spend a lot of time debugging system issues that result from seeing a processor ROB timeout. The purpose of this paper is to give context and guidance to help hardware engineers and software engineers troubleshooting these issues.

Typically processors indicate a ROB timeout with an IERR# signal assertion. Interestingly IERR# assertion does not mean ROB timeout condition only, this means that the processor has experienced an internal error, and it may be a result of issues such as an error condition in the cache unit, error conditions in the internal bus etc.

For processors that support the Intel Quick Path Interconnect interface, there is no longer IERR# or MCERR# signals from the processors. Instead they have been replaced by the CATERR# signal pin to indicate that a catastrophic error condition has been experienced by the processor.

If the Machine Check capability of the processor is enabled, this event can also be recorded in the Machine Check Status register. The processor ROB timeout is only one of the Machine Check events that can be recorded. This paper will only focus on the processor ROB timeout error condition, and provide guidance on debugging this Machine Check event.

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