Greetings, all.
We're using about a dozen net4826 boxes here, and we need to connect
a few USB devices to each box via a single USB hub.
We power each net4826 box using PoE supplied by an HP PoE switch,
through a D-Link DWL-P50 PoE "splitter" (12V output). (As you know, we
need the splitter because the net4826 isn't PoE standards-compliant,
and the splitter puts the power on a pair the net4826 can use.)
We originally intended to power each net4826's USB hub over USB
itself, and the USB devices from that USB hub. But we found the USB
devices in the numbers we need draw too much power for that, so we've
had to fall back on powering the USB hub by other means.
Since we have PoE readily available, we decided to power each USB hub
using the 5V output of a dedicated D-Link DWL-P50 PoE splitter (each
supplied with power by a dedicated PoE switch port).
We use D-Link DUB-H7 USB hubs.
So in full, the picture is:
PoE 12V
port0 ------------> DWL-P50 ----> net4826
/ |
HP PoE switch | USB cable
\ |
port1 ------------> DWL-P50 ----> DUB-H7 USB hub
PoE 5V
Note that no USB devices are hanging off the hub in any of the cases
I'm describing.
We find that while the net4826 can talk to the USB hub when the USB
hub is *not* externally powered (i.e., unplug the 5V cable in the
above picture), the net4826 fails to talk to the USB hub when the USB
hub *is* externally powered.
In fact, it's worse than that: when we power the USB hub using PoE,
and connect its USB cable to the net4826, the net4826 hangs
immediately, and resets upon our disconnecting the USB
cable. Moreover, we seem to have *permanently* killed the internal USB
hub on at least one of our net4826 boxes by connecting an externally
powered USB hub in this way.
Before you tell me that we're powering the hub incorrectly, consider
that when we power the USB hub in exactly this way over PoE, it works
flawlessly when connected to *any other* type of desktop PC we've
tried.
Even more strangely, when we power the USB hub not using PoE, but
using the AC adapter supplied with the USB hub, the USB hub works
*fine* when connected to the net4826. But the AC adapter and PoE
splitter output are both extremely close to 5V.
So, in sum, it appears that we can't power *both* the Soekris *and*
the USB hub from PoE (even though they're separate PoE ports, and the
switch has ample power capacity) without the failure mode described
above. Change anything (power the USB hub by AC adapter; substitute a
desktop PC for the net4826) and things work fine.
We're mystified. Has anyone seen behavior anything like this
elsewhere, or might anyone have a hypothesis as to why PoE behaves so
strangely with this combination of devices?
We're trying to find a work around as quickly as possible, as we need
to purchase dozens more small PCs ASAP. We'd like to use more
net4826es, but the problem with USB and PoE is a showstopper for us,
as the main role of these boxes in our lab is to control USB devices.
Many thanks,
-Brad, [EMAIL PROTECTED]
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