I have a LeMaker HiKey and I'm having trouble getting the network running in a preferred configuration. The HiKey is an inexpensive ARM64 development board running Linaro. Linaro is a lot like Debian with an LXDE desktop, and in effect, this is a mini-desktop with an ARM CPU architecture.

The board is powered and has two USB ports and a micro USB port. However, the board lacks an ethernet port. The USB ports do not power attached devices, so I need to use a powered hub when using them.

If I use an Ethernet-to-USB adapter with a powered hub, then the device has network connectivity. If I remove the powered hub and provide Power over Ethernet (PoE+) to the Ethernet-to-USB adapter, then the device loses its network connectivity.

I tried 3 different Ethernet-to-USB adapters with the same results, so I am missing something. I think this is a case of me not knowing what I don't know. Can anyone explain to me what I am missing in the configuration using Power over Ethernet?

(I am trying to avoid a PoE injector in the adapter. That is, I don't want to have to plug the Ethernet-to-USB adapter into a wall socket. Its the reason I purchased a Power over Ethernet switch).

  • are you using a POE splitter too? en.wikipedia.org/wiki/Power_over_Ethernet#/media/… Notice the device that gets powered doesn't get powered over ethernet. Power seems to come out of the ethernet socket, through an ethernet cable, goes to a splitter which has a regular ethernet with a power cable, and those plug into your device that device that requires ethernet and power separately. – barlop Jan 14 '16 at 5:29
  • @barlop - No, there is no splitter. – jww Jan 14 '16 at 5:30
  • Does the USB -> Ethernet adapter work correctly when directly connected to the board without using a hub (I'm taking the word hub to mean a USB hub, I'm not sure though)? I've only ever seen USB -> Ethernet adapters that are USB bus powered. Can you provide a link to your USB -> Ethernet adapter? – Jonno Jan 14 '16 at 5:31
  • this may be a good usb ethernet adaptor. The anker usb-ethernet adaptor. . Somebody recommended it to me once saying it had a good chipset and i think they said it was back compatible with usb2 and from what i recall, it was. No external power required. – barlop Jan 14 '16 at 5:34
  • @Jonno - no, a direct connection does not achieve network connectivity. The line definitely needs power. – jww Jan 14 '16 at 5:37

For PoE to work, both ends of the Ethernet link carrying power need to support the same flavor of PoE. I've never seen a USB Ethernet adapter that supports receiving (acting as the "powered device" (PD), not the power supply for) any flavor of PoE.

I doubt a PoE-receiving USB Ethernet adapter exists, because PoE is thought of as a way to power whole remote embedded devices, not just their NICs, and I don't think there's a commonly implemented way for a USB device to power a USB host (not until USB type-C, that is).

So you won't be able to make this work until/unless you find a USB Ethernet dongle that is designed to act as a PoE receiver for the same flavor of PoE as your PoE-supplying hub/switch/midspan power supply (power injector/splitter) supplies.

  • Thanks Spiff. The frustrating thing for me is the board is headless. I SSH into it. The only USB connection is Ethernet and it appears to need power. If the damn adapters would tap PoE for power instead of looking for it on the USB side, then all these troubles would go away. – jww Jan 23 '16 at 2:46
  • @jww I feel like I could help you better if I understood your constraints. How does the HiKey board get power? If it already uses a wall-wart power supply, why can't you plug a small self-powered (meaning, one that uses its own power supply, as opposed to "bus powered" ones that have to receive power from the USB bus) USB hub's wall-wart power supply into the same outlet? Also, since you already have a PoE switch to act as the PSE (Power Supply for Ethernet; the power injector), couldn't you just use the "receiver half" of a standards-compliant PoE splitter to power your self-powered USB hub? – Spiff Jan 23 '16 at 2:55

I've been looking for a similar device that would let me do this without an ethernet adapter, a PoE usb splitter and a Y-cable and this is the closest I've found so far. It uses USB-OTG to connect the ethernet adapter directly to the device while also providing power.

And a similar solution for USB-C+PD:

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.