Device Family: Intel® Arria® 10, Intel® Arria® 10 GT, Intel® Arria® 10 GX, Intel® Arria® 10 SX, Arria® V GZ, Stratix® V GS, Stratix® V GT, Stratix® V GX

Type: Answers

Area: Intellectual Property


Last Modified: March 29, 2017
Version Found: v15.1 Update 2

Why does the Hard IP for PCI Express in Gen3 configurations, periodically transition from the L0 LTSSM state to the Recovery state then back again?

Description

A Gen3 Hard IP for PCI® Express instance may transition from L0 to Recovery and back again if the receive(RX) Physical Coding Sublayer(PCS) receives data that is identical to a SKP or SKP END pattern.  The PCS block synchronizer will incorrectly interpret these as valid SKP Ordered-Sets and re-align the data. This results in the data block boundary being corrupted.  This will not cause data to be lost because the affected data will be re-transmitted after the LTSSM returns to the L0 state.
 
The signature of this event on the PIPE interface is as follows:
·         The PIPE rxdata of the affected lane matches the SKP data pattern (AAAAAAAA, AAAAAAAA) or SKP END pattern (AAAAAAAA, XXXXXXE1).
·         The PIPE rxvalid signal of the affected lane de-asserts until the LTSSM recovery event ends.
·         The PIPE rxstatus signal of the affected lane reports 3’b100 (decode error or disparity error).
 
It is rare that scrambled data will exactly match a SKP pattern or SKP END pattern.   Some systems may see this occur once every few hours. This issue has negligible effect on the link bandwidth. 

Workaround/Fix

There is no scheduled workaround or fix for this issue. No action is required.