On Wed, 13 Sep 2006, Phil Endecott wrote: > Thanks for the quick reply Alan. > > Alan Stern wrote: > > On Wed, 13 Sep 2006, Phil Endecott wrote: > >> Has anyone ever tried to couple a device controller (gadget) and a host > >> controller on the same processor to make a transparent feed-through USB > >> channel? > > > Other people have suggested this in the past. Unfortunately it can't be > > done. A USB bus analyzer needs to receive every packet on the bus, but > > a USB device controller will receive only packets addressed to itself. > > Maybe I shouldn't have said "analyser"; a real analyser would be a > passive device, while what I'm describing certainly isn't. I imagine a > "real" device being plugged in to this "analyser" which clones its > descriptors on its device interface. So it could only work with one > thing plugged in (unless there is some way to make the device interface > appear to be a hub).
This might be possible. Although it certainly wouldn't work if the one device plugged in was a hub! That is, the host would be able to talk to the hub but not to anything behind it. Potential difficulties include changes in packet timing caused by the intermediate processing in the feed-through channel and the possibility that your device controller might not support as many endpoints as the device you want to monitor. > > There are other technical reasons why this can't be made to work, such as > > the electrical constraints on voltage, current, and impedance in the USB > > signal lines. > > Can you elaborate on this? Those reasons don't apply here -- I was thinking of the passive "analyzer" situation. Alan Stern ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Linux-usb-users@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-users
