On Sun, 13 Feb 2005, Uwe Bonnes wrote: > No, > > I don't want to say that the device runs at 480 Mb/s . It is a Full Speed > device and behaves that way, running at 12 Mb/s. But what I am trying to say > is, that the frequency, at which pending control messages sent to the device > is > different. These control messages make some port pins switch ( one single > change per usb control message per port pin). I can view and measure these > changes with an oscilloscope. Connected to the USB 2.0 Hub the frequency of > changes is 8 kHz, while connected directly to the PC this frequency is 1 > kHz. > > From what I understand, for USB 2.0 devices on a 2.0 bus, these messages are > sent at 8 kHz (microframes), while 1.x devices only expect messages at 1 kHz > (full frames), and so do 2.0 devices on a 1.X bus. > > Device hardware and bus are version 2.0, however the device is not high speed, > but only full speed, but also fully USB2.0 spec compatible.
Now I understand your question. The rate at which control messages are sent to the bus depends on factors other than the controller speed. It's possible for a driver or program to "queue" messages (submit more than one without waiting for the first one to complete). Queued messages are sent to the bus about as fast as possible: Each is sent as soon as the acknowledgment for the previous one is received, without regard to 1 kHz or 8 kHz frame boundaries. However completion of messages is reported to drivers only at a frame or micro-frame boundary. If a driver or program waits for the first message to complete before submitting the second, then the behavior you observed would result. Hope this helps, Alan Stern ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-users
