> > > Maybe ISO is more like a wire that carries a signal. Once the > > > host sets a configuration which contains ISO endpoints, these wires are > > > all "hot" and "signal jitter" is up to the functions on either end to > > > deal with in their own way. > > > > I suspect that's closer to the right model. Look at the "sync frame" control > > request (9.4.11 in USB 2.0 spec). Somewhere I've seen some extensive > > adaptive models for how ISO synch is supposed to be maintained. > > Though note that for Linux-USB, the reservation comes when an URB > > is submitted, not when the configuration is set. > > > > Really? That surprises me because in 5.6.3 of the USB 1.1 Spec it > states:
You should use the USB 2.0 spec for all new work, BTW ... section numbers are the same everywhere I've had occasion to notice, but errata have been incorporated as well as updates for high speed. For example, 5.6 is still about ISO, also 5.12 which is probably the section I was thinking about. > "An endpoint in a given configuration for an isochronous pipe specifies > the maximum size data payload that it can transmit or receive. The USB > System Software uses this information during configuration to ensure > that there is sufficient bus time to accommodate this maximum data > payload in each frame. If there is sufficient bus time to accomodate the > maximum data payload, the configuration is established; if not, the > configuration is not established". Think of it this way: "configuration" is not the same as invoking a SET_CONFIGURATION request. Linux-USB configures the bandwidth allocations on-demand ... :) > Come to think of it, even if Linux-USB conformed to this, class drivers > could work around it by using SET_CONFIGURATION behind the subsystem's > back. There are some requests, like SET_CONFIGURATION, which drivers must not make themselves since usbcore needs to update host side state to match. It'd be worth identifying and documenting those requests! - Dave _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
