FreeLists / si-list / [SI-LIST] NPU / DDR interface bug issue

["BOUTHEMY JEAN PIERRE" <Jean_Pierre.Bouthemy@xxxxxxxxxxxxxxxxx>]

=20
Hello SI experts,

I have to solve for a DDR interface issue when traffic is full bandwith
(1Gb/s): DDR is then blocked and we can not access to it anymore.=20
Note that this "should not be" a card bug because it happens only on a
few cards, about 2 or 3 protos among more than 100 cards.=20
FYI, the Controller is an Intel Network Processor IXP2400 and the DDR
interface is running at 150MHz.=20

On one of the fail cards, I have soldered some wires (about 3" long) on
a few signals (CS, WE, RAS, CAS, CK, DQS0 and DQ0) and attached 4 probes
on CK, WE, DQS0 and DQ0. I have launched the full bandwith test on this
card and observed that it is now running OK for more than 118 hours
without failing!!=20

The scope signals are very poor on the scope (scope + probe bandwith >
6GHz) because of the too long wires and the ground connection which is
very poor.=20
But I can not understand why the interface is running OK for more than 5
days, whereas it normally fails before 2 minutes of full bandwith test!!


Has someone already experienced such a case?=20
Could you please explain if some stubs on signals could make the signal
integrity better, or ameliorates a timing, or so ...=20

Please remember that only 2 or 3 cards among more than 100 have this
issue, which means that it "should not" be a design issue.=20

Thank you for your help,
Regards,=20

Jean-Pierre.=20
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