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 ETH problem 
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Joined: 15 Aug 2013, 05:48
Posts: 11
We got a problem with the Ethernet interface.

Carambola ETH - some Ethernet switches: ok, LINK LED comes immediately.
Carambola ETH - Carambola ETH: ok, LINK LED comes immediately.
Carambola ETH - some other devices: ok, LINK LED comes immediately.
Carambola ETH with one specific device: LINK LED comes after 1 .. 30 minutes (!), after that we get a stable connection.
This specific device - Ethernet switch: ok, LINK LED comes immediately.
Our Carambola HW or Carambola evaluation board: same behaviour.
Normal patch cable / crossover cable: same behaviour.
Old Carambola FW / newest FW: same behaviour.
Same power source / different power source: same behaviour.

Has anyone ever seen something similar?

I do not think it's a Carambola problem, but maybe there is a Carambola solution. There are many AR9331 PHY mode bits, for example MDI / MDIX / auto crossover. I have very little Ethernet knowledge and it seems to me very time consuming to change a bit in the firmware, compile, flash, try. According to AR9331 data sheet, a soft reset is necessary to change the bits. I do not know if it is possible to change the mode from a running system.

Addendum: Maybe ethtool can do this, I will give it a try.

Addendum 2: ethtool -> setting MDI not supported :-(

07 Jun 2017, 07:42

Joined: 15 Aug 2013, 05:48
Posts: 11
Meanwhile the cause is clear: The HW on the other side is using a DM9161A PHY, which in rare cases has a problem with some ethernet chips. AR9331 is such a rare case.

In these rare cases auto negotiation does not work. With ethtool on eth1 I am able to switch off auto negotiation and set a fixed speed. Now the link is established immediately. I do this with a script in /etc/hotplug.d after eth1 comes up.

ethtool works with only eth1, since eth1 is directly connected with the CPU. eth0 is connected via the AR9331 internal switch and therefore the tool swconfig has to be used. But swconfig can only read the settings, not write.

09 Jun 2017, 05:33

Joined: 07 Dec 2011, 16:01
Posts: 503
Location: Lithuania
Thanks for the info.

09 Jun 2017, 07:05
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