During host enumeration, at what point should a USB device switch to HighSpeed (if supported)? Should it be running HS after the first reset, or after the second? In response to the get_device_descriptor, should the device always return its descriptor indicating that it is USB2 compatible? Thanks.
"Graeme" wrote in news: snipped-for-privacy@uni-berlin.de:
This is all described in Section 7.1.7.5 "Reset Signalling" in the USB 2.0 spec, which you download from
The low/full speed detection is performed using the device pull-down or pull-up resistors, and high speed is detected using low level signalling during the reset sequence.
If the device is HS capabale, then it should be running at HS after reset completes, if the upstream hub is also HS capable (otherwise the device will be using FS signalling).
You need to read the USB spec to understand this properly, particularly chapters 7 and 9.
AndyM
Thanks. The device that I'm using is supposed to be HS capable, but only seems to want to work in FS mode. I've read that USB spec section and I am assuming this is all handled in my device (I can't get support from the manufacturers). My device is happy in FS mode, and it is plugged into a HS capable port (verified with another USB2 device). When I change my device_descriptor to indicate that it is USB2.0 (and not 1.1), then WinXP gives me a warning saying that I have a USB2 device in a non-HS port. Why would it say that? Is it because the low level signalling has failed in some way, and my device is still in FS mode. Do you know if WinXP always gives this warning if you plug a HS device into a non-HS port?
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.