tqm 8260 scc ethernet crc errors

[Thomas Geffert]

Hello,

I've problems with receiving packets with an TQM8260 board on the SCC
10Mbit ethernet interface.

If I connect two tqm boards directly via an ethernet crossover cable and
send udp packets from one board to another the receiving CPM marks
1-15% of all packets with an crc error flag (this depends on packet
size and send speed).  When I check the udp checksum of the received
packets this check only ails for approx 5-10% of the marked packets,
e.g.

Send packets in 5s      CPM says CRC-Error[1]   UDP checksum error
=====================================================================
6000 (512 bytes each)   591 / 9.8%              94 / 1.6%
4850 (512 bytes each )  220 / 4.5%              34 / 0.7%

6000 (128 bytes each)   182 / 3%                43 / 0.7%

The faster the packets are send and the longer the packets are the more errors
are detected. If I send the packets with a rate <50 packets/s I got almost
no crc errors.

I'm very surprised over the errors, as I use a direct connection
between the boards and send only in one direction. In such a case I
would expect to get no errors. Can this be an EMI error of the
physical SCC ethernet interface of the tqm boards?

I also connected the tqm board via a switch to a PC 10Mbit ethernet
interface and got slightly smaller error rates, but they are still
there. If I use the FCC ethernet interface I don't get this problems.

Did anyone make similiar experiences or has an idea how this errors can happen?

I use the DENX linux-2.4.4-2002-10-06 (patched for RTAI linux 24.1.10)
and enabled full duplex mode in the SCC enet.c driver (without full
duplex I got also crc errors and lots of dropped packets).

Thomas Geffert

Footnotes:
[1]  I got this value from the scc1 parameter ram field crcec.

--
Dipl.-Ing. Thomas Geffert
KEYMILE / Datentechnik Intercom GmbH
Frankenring 14, 30855 Langenhagen, Germany
Tel +49 (0)511 978197-669 / Fax +49 (0)511 978197-670
mailto:thomas.geffert at keymile.com / http://www.keymile.com

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