Problem DescriptionThe network services engine (NSE-1) may hang due to a timing problem with the CPU SysAD bus and the read bypass circuit causing bus contention on the Route Processor (RP) SysAD bus.
BackgroundThere is a circuit on NSE-1 called the read bypass circuit that allows read cycles to avoid going through the Field-Programmable Gate Array (FPGA). This circuit works by latching the sysad data from the CPU and then, if it is a cycle that can use the read bypass, redrive the latched data to the Network Controller Board (NCB). The basic problem is that the read bypass drives on the very next cycle and this may cause bus contention as the CPU gets off the bus and the read bypass transceivers begin driving the bus.
This issue occurs during normal operations on boards with susceptible parts, such as boards with slower than typical CPUs and faster than typical read bypass transceivers.
Problem symptoms include the error messages listed below. The failure can also result in a complete hang of the router.
When the NSE-1 hangs, the router will not recover on its own, will not respond to console "break" or to the faceplate push button Non-Maskable Interrupt (NMI).
Examples of error messages encountered during problem manifestation are as follows:
CACHE PARITY EXCEPTION
DATA PARITY EXCEPTION
CACHE ERROR EXCEPTION
Note: Even though this has been identified as a bus contention issue ensure you have viewed the 7200 Fault Tree document to rule out other potential issues, such as watchdog timeout or a single event upset (SEU or PMPE) that are not part of this Field Notice.
Cisco recommends a fix-on-fail strategy for this problem. There is no workaround available.
As of approximately June 2004, new products that were manufactured under Engineering Change Order (ECO) E076743 are guaranteed to be free of this problem.
Refer to How to Identify Hardware Levels below for instructions on how to view the version of in-service product.
Service Logistics has known-good inventory at this time.
The standard RMA process and delivery times are in effect.
Refer to the How to Identify Hardware Levels section to confirm that the suspect NSE-1 unit(s) are properly identified as being within the range of product affected with this issue.
How To Identify Hardware Levels
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