[ixp1200] Debugging ETH ports of IXP1200

[Magesh Kannan]

Hi,

This is a follow-up to my earlier emails about not being able to connect
the Fast Ethernet ports on the IXP1200 to a PC using a straight-thru
cable. Here is a recap.

If I connect any of the ports on the IXP1200 to an ethernet card on a 
Linux PC, the two LEDs on the IXP1200 port (which I think stand for
Activity and Full-Duplex) and one of the eight LEDs in the middle (which I
think is the Link LED) blink at regular intervals (even when no data is
being transmitted) and no link seems to be established. If I run the
diagnostic tool 'mii-diag' on the Linux side, this is the output I get.

================
Basic registers of MII PHY #1:  3100 7809 0181 b802 01e1 41e1 0003 0000.
 The autonegotiated capability is 01e0.
The autonegotiated media type is 100baseTx-FD.
 Basic mode control register 0x3100: Auto-negotiation enabled.
 Basic mode status register 0x7809 ... 7809.
   Link status: not established.
 Your link partner advertised 41e1: 100baseTx-FD 100baseTx 10baseT-FD
10baseT.
   End of basic transceiver information.

Monitoring the MII transceiver status.
17:13:19.731  Baseline value of MII BMSR (basic mode status register) is
7809.
17:13:34.036  MII BMSR now 782d: Good link, NWay done, No Jabber (41e1).
   New link partner capability is 41e1 0003: 10/100 HD+FD switch.
17:13:34.326  MII BMSR now 7809:   no link, NWay busy, No Jabber (0000).
17:13:41.236  MII BMSR now 782d: Good link, NWay done, No Jabber (41e1).
   New link partner capability is 41e1 0003: 10/100 HD+FD switch.
17:13:41.396  MII BMSR now 7809:   no link, NWay busy, No Jabber (0000).
17:14:00.106  MII BMSR now 782d: Good link, NWay done, No Jabber (41e1).
   New link partner capability is 41e1 0003: 10/100 HD+FD switch.
17:14:00.136  MII BMSR now 7809:   no link, NWay busy, No Jabber (0000).
17:14:09.846  MII BMSR now 7829:   no link, NWay done, No Jabber (41e1).
   New link partner capability is 41e1 0003: 10/100 HD+FD switch.
17:14:09.856  MII BMSR now 782d: Good link, NWay done, No Jabber (41e1).
17:14:10.366  MII BMSR now 7809:   no link, NWay busy, No Jabber (0000).
17:14:12.076  MII BMSR now 7829:   no link, NWay done, No Jabber (41e1).
   New link partner capability is 41e1 0003: 10/100 HD+FD switch.
17:14:12.086  MII BMSR now 782d: Good link, NWay done, No Jabber (41e1).
================

The same behavior results with different NICs on the Linux side, one using
eepro100 driver and another using the tulip driver on Linux 2.4.3-12.

As you can see from the output, the link seems to be flapping. I am sure
that the cables that I use are fine (I tested them using a cable tester,
connected them on other machines and even used a factory-made CAT5
cable). To cross-check this problem, I also connected one of the IXP1200
ports to a port on a Cisco Catalyst 3500 series switch and observed in the
switch's console port that the concerned ethernet port was going up and
down fairly regularly.

Has anyone seen this before? Given this behavior, is there a way to debug
the ethernet ports on the IXP1200 board? In particular, is there a way to
find out what speed the MAC has decided on and if possible, disable
autonegotiation?

FYI, if I interconnect two ports of IXP1200 with each other with a
crossover cable, the link is established fine, the yellow LED on the port
is lit and link LED is also up.

Thanks for your help,
Magesh