I have a USB device whose driver causes a BSOD (XpProSP2) when the device is
plugged in to an externally powered hub and then that hub loses AC power. The
BSOD happens within 5 seconds of disconnecting AC power from the hub, and no
login or software is necessary to trigger the BSOD, i.e. it can happen right
after a reboot.
I've contacted the manufacturer about it, and it's certainly a bug in their
driver, but I'm trying to understand what the failure mechanism might be.
The device draws only 40 mA and could be powered directly off the bus. The
device is the only one plugged into the hub.
Does anyone know:
1. What should happen when a usb hub unexpectedly loses external power,
according to the usb spec? I'd expect the hub should try to "unplug" all its
client devices so the usb host sees them go away gracefully, but maybe not.
2. How does Windows detect/handle a hub going away unexpectedly? Does it
generate a WM_DEVICECHANGE for all the formerly connected client devices?
Clearly the driver isn't getting notified or else it's just not handling this
exceptional case correctly.
3. Ever heard of another device behaving badly when its hub loses power?
Thanks for any insight.
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