On Wednesday 27 April 2005 8:03 am, Olav Kongas wrote: > > On Wed, 27 Apr 2005, David Brownell wrote: > > > On Tuesday 26 April 2005 10:08 am, Alan Stern wrote: > > > On Tue, 26 Apr 2005, Olav Kongas wrote: > > > > > > > Also, remote wakeups can result in resuming of root hub only > > > > if device is not suspended. Was that correct? > > > > No; remote wakeup wakes up the device that was suspended plus any > > parent devices that were suspended. If the device wasn't suspended, > > then it can't be woken up... > > David, in my question above, by 'device' I meant HC. That > bit of the context got lost by multiple replies/deletions.
OK, in that case the answer to your question is hardware-specific. As a rule, HCs can be viewed as bridges with "downstream" links (the root hub, talking USB protocol) and "upstream" links (to some platform bus, like PCI). And those two links can support suspend states somewhat independently of each other ... as in, the downstream link can be suspended while the upstream one is still working, though normally not the other way around. All HC hardware I've had occasion to look at can support remote wakeup of the root hub when the upstream link is still active. And as a rule that's not even board-specific; chip designers take that as a goal, evidently to satisfy what the USB spec (bogusly) calls a "global" (to that single USB tree) suspend. But supporting wakeup of that upstream link is more complex, and can be board-specific. Some systems don't support separate suspend modes for that link, just "off". Others manage the root hub separately enough that it can maintain suspend state even if the HC itself is powered off. (See how EHCI is specified; the root hub ports for PCI can go in the vAUX power well.) When root ports are powered, and D+/D- monitored for the "K" state (remote wakeup, vs normal "J" state during suspend), then the HC overall can be "resumed" even if the other HC state is fully powered off and unclocked, and must be fully reinitialized. And of course there's also "just leave it powered up and call that suspend". - Dave ------------------------------------------------------- SF.Net email is sponsored by: Tell us your software development plans! Take this survey and enter to win a one-year sub to SourceForge.net Plus IDC's 2005 look-ahead and a copy of this survey Click here to start! http://www.idcswdc.com/cgi-bin/survey?id=105hix _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
