On 1/13/17, Greg KH <gre...@linuxfoundation.org> wrote: > On Fri, Jan 13, 2017 at 07:24:10PM -0800, bruce m beach wrote: >> Hello everybody >> >> I have been stuck for ages trying to figure out something >> in the Standard USB Descriptor during the enumeration. It >> looks like it should should be quite simple but I am not >> getting it because maybe some mind block, maybe becuase the >> documentation is unclear, or maybe because I'm brain-dead. >> Here is the problem: >> >> I think the host starts out requesting the device descriptor >> This is okay and works no problem. At some point the host >> requests the configuration descriptor and I get stuck. The >> usb 2.0 spec. says: >> >> "When the host requests the configuration descriptor, all >> related interface and endpoint descriptors are returned" >> >> How is the host supposed to know how much data is coming in >> or how much data to request until it reads wTotalLength? >> >> I would assume the host would request the 9 bytes of the >> configuration descriptor, then make subsequent requests to >> get the interfaces and endpoints but for instance in the >> section on the interface descriptor the spec says >> >> " An interface descriptor is always returned as part of a >> configuration descriptor. >> >> Again how is this supposed happen if the host is only >> requesting 9 bytes in the configuration descriptor stage > > Have you looked at the data on the wire? The host asks for 9 bytes, and > then it uses the information there to get the "real" size of the > descriptor and then it asks for the full descriptor with all of the > information in it. > > hope this helps, > > greg k-h >
Yes it helps. Makes sense. I made some changes and can get the descriptors from a userland program so I know its working (i.e. from userland I can upload firmware and have control over the chip includeing the usb subsystem) but at this point after a reset there is no re-unumeration. It justs lists the original configuration.(using lsusb). Notice I am using ioctl's. Bruce -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
