Re: sun neptune mis-detecting ethernet crc faults?

Chris Friesen wrote:

Hi all,

David Miller is busy and suggested someone on the list might be able to
help.

We have some boards using the Sun Neptune ethernet adapters.  We're
seeing behaviour that at this point looks like a hardware glitch
in the ethernet CRC validation on the receive path.  It appears to be
incorrectly detecting a corrupt CRC and dropping the frames.  (We've
enabled port mirroring on the switch and the frames are received without
errors on the eavesdropper board.)

A simplistic question, but are you sure that the eavesdropper board is checking CRCs?

The odd thing is that we're using a TCP connection and once the CRC
glitch shows up for a particular chunk of data it continues to drop all
the retransmissions for that chunk as having bad CRCs, even though their
CRC values are totally different due to different embedded timestamps.

Do you mean TCP timestamp options?

Has anyone heard of anything like this on the Neptune hardware?

Can't say as I have, but the history of "networking" is littered with data pattern induced bugs in all manner of hardware.

MTU is set to 2000 if it matters, though we're planning on retesting
with it set to 1500.

An MTU of 2000 bytes means a TCP segment with timestamps enabled will be 2032 plus the ethernet header (assuming no vlan tags) of 14 bytes for 2046 and then there is the trailing CRC - which is getting very close to a magic power of two boundary, another place where history is repleat with examples of bugs.  One that comes to mind is that the old Alteon AceNICs got very unhappy if one crossed a 4G boundary with a DMA...

rick jones

I'm considering disabling the hardware CRC check as a
verification--looking at the niu driver I think I should be able to do
this by not including XMAC_CONFIG_RX_CRC_CHK_DIS in the big list of
flags being OR'd in niu_init_rx_xmac().

Anyone have any suggestions?

Thanks,

Chris
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