Markus wrote: > my question is slightly off-topic since its affects a property of > USB that's presumably standardized. Nevertheless, I'm unable to > find any definite information on this: > > Is it correct that the root hub of a host controller has always > address 255 on the given USB bus?
No, 255 is an arbitrary value that Pete chose to assign to root hubs in the Windows backend, and is not a valid device address per the USB spec. On other operating systems the kernel API that backends use expose root hubs like if they were external hubs, so there no address is invented. USB 2.0 10.2.8 Root Hub: The root hub provides the same functionality for dealing with USB topology as other hubs (see Chapter 11), except that the hardware and software interface between the root hub and the Host Controller is defined by the specific hardware implementation. EHCI: System software should provide an abstraction to the USB system software stack that allows the root hub ports to be manipulated by the system as if they were ports on an external hub. I'm sure Microsoft allows the same port manipulation, but they don't expose the root hub as if it was an external hub, and since the root hub isn't an actual USB device it doesn't have a device address. > If this is the case, then there are device addresses 0 to 126 + > 255 (the root hub), correct? The device address is a seven-bit value. 0 is the default address, until a device is assigned a unique address by the OS. 127 is also a valid device address. 255 is not. I think the good way is for the WinUSB backend to not fabricate a root hub device, since it can never be communicated with anyway. What is the libusb-win32 situation in this regard? Does Windows agree to use libusb0.sys for a root hub? //Peter ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ libusbx-devel mailing list libusbx-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libusbx-devel
