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Cisco Bug: CSCtb88166 - SRAM parity exception on SIP-400

Last Modified

Mar 01, 2018

Products (1)

  • Cisco 7600 Series Routers

Known Affected Releases

12.2(33)SRC 12.2(33)SRD

Description (partial)

Symptom:
This DDTS addresses the specific case of SRAM parity exception on TCAM lookup on SIP-400.
These exceptions are rare events, but have been reported once/twice on a SIP-400 linecard on various releases.
Always the address location corresponds to TCAM result buffer location for the ME context issuing TCAM lookup.
After collecting several such crash dumps, we could conclude that in all cases, exception occured on the upper word (4 bytes)of TCAM result buffer. This information was provided to NetLogic.
As per Netlogic, (e-mail threads attached), the upper 32-bits of the result buffer(result is 8bytes) can be stale data if the TCAM result status (upper 2 bits of the lower word)is "NOT READY". If the upper 32-bits of the result are read when the above status is "NOT READY", this can cause parity exception.
Also, a minimum of 10 QDR cycles (80 ME cycles as QDR is operating at 175Mhz and ME @ 1.4GHZ), is required after issuing a TCAM instruction before the TCAM result status is read, if the result buffer is read too early, then SRAM parity errors can be seen on upper or lower 32-bits of the result buffer. 

Conditions:
As per Netlogic, (e-mail threads attached), the upper 32-bits of the result buffer(result is 8bytes) can be stale data if the TCAM result status (upper 2 bits of the lower word)is "NOT READY". If the upper 32-bits of the result are read when the above status is "NOT READY", this can cause parity exception.
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