BestComm engine has some data cached internally and that it detects a write to the address from where those data comes, he will invalidate his cache.
But when the kernel writes data to the skb buffer, they may partially stay in cache so there won't be any transaction at all on the xlb bus. It's when bestcomm will read the skb, that the core will snoop the bus, detects there is a read request for some data he has in cache, force a retry of the bestcomm read, write the data to memory (via xlb), and finally let bestcomm retry the transaction to fetch the good data. So I guess what "could" happen is that : - The kernel allocate a skb, but it ends up being as the same memory location as a "previous" one. (or maybe in a directly following position because of prefetch). - You submit it to bestcomm - When bestcomm does the read, since the skb was used "just before", the line is still in cache but with the wrong data. Since the kernel just wrote the data, there was not yet a xlb transaction because the data are still in cpu cache. Bestcomm think he has the data (no xlb write so it's cache was not invalidated), so he doesn't generate a xlb read. But if there is no xlb read the core doesn't get a chance to snoop it and doesn't flush it's cache ... Although that doesn't explain why setting BSDIS high solve the problem, nor why there is only 1 byte wrong ... Have you checked your XLB snoop window setting ? And that core snooping is enabled ? Also that you don't use the "nap" power saving feature of the core ? (it disables snooping altogether ...). Sylvain ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________