On Tue, 19 Feb 2013 13:27:49 -0500 (EST) Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > Adding a completely new API that returns a timestamp associated with > > the start/end/fixed offset of a frame number sounds like a perfect > > solution for my problem. I am not sure what you mean with completion > > (interrupt). AFAICS that term is used mainly/only in relation to > > (signaling) completed URBs. How does that fit together? What can I do > > to make it happen? > > Yes, completion interrupts are used for signalling when an URB > completes. That's most of the signalling the CPU gets from a host > controller; other things like port connect and disconnect are > comparatively rare. Hm but there are also other potential interrupt sources at least for some HCD types that could be used, e.g. OHCI_INTR_SF at the start of frames in OHCI or the Frame List Rollover interrupt in EHCI? The drawback of using other interrupt sources like OHCI_INTR_SF would be of course that they... interrupt, a lot :) Maybe the gathering through normally unused interrupts could be enabled/disabled with ioctls (and while that is disabled the value is only updated on completed URBs)? > The way they fit together is that completion IRQs are raised at > microframe boundaries. Hence, if the interrupt handler stores a > realtime clock value together with the new microframe number, there's > no need for polling. > > The drawback, of course, is that there won't _be_ any completion > interrupts until an active URB completes. Presumably that won't be a > problem for you, but it is a weakness for a general-purpose API. Yes, that is not very nice in general, but it's certainly an improvement over now. What kind of interface do you propose? I would say a single file in sysfs with one line frame counter and one line timestamp, but the sysfs docs clearly don't encourage mixing types like this, if I understand it right. Of course we need to make sure that the corresponding values can be retrieved safely in sync... Do you know about a comparable API I could look at? -- Kind regards/Mit freundlichen Grüßen, Stefan Tauner -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
