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Beagle Bone Ethernet PHY problem

Steven Liu1
Expert 4455 points

Hi,

  In my testing on am335x beagle bone, I've met an issue related to Ethernet . The Ethernet PHY can’t work normally at times if I pull out the cable for more than 30s. After reconnecting the net cable, It doesn't work any more. I've check the "dmesg", nothing happened after "PHY: 0:00 - Link is Down ". Then if I pull out and reconnect again, it is possible to work again but not succeed every time.  

  But this issue never happen when I tried to connect the beagle bone to switch but not router. And When connected to the router, using cross-line instead of direct-line can help to solve the problem in larger extent. 

  Does anybody met this before or has any idea what's the reason?

  Thanks.

  Steven

  • 0
    Intellectual 810 points

    I don't know if it's relevant or not, but we manufacture a variety of Ethernet devices, both from our own design as well as using plug-on modules from various manufacturers.  We've noticed that certain switch/router devices from certain equipment manufacturers can be more sensitive to connecting to some devices: it appears to be the physical layers adversely interacting.  Sometimes during production test we'll test 100 units on a certain switch that we normally use, but maybe 1 or 2 won't get link reliably.  But if we use a different switch then all 100 devices are bulletproof.  So for us we see a difference between Linksys, Cisco, Dell, DLink etc. devices.  Sometimes this also seems to extend to sensitivity to the cables involved, but seemingly to a much lesser extent than the switch itself.

    When you say you are using a switch and a router, are they from different companies?  That alone (with all other variables such as power and grounding etc.) could be the origin of the issue: if you have a certain device that works reliably 100% of the time, I'd suggest sticking with that device during development to avoid chasing software ghosts when the hardware is potentially to blame.

    Darrin