Re: USB interrupt URB programming question
Alan Stern <[email protected]>
| Newsgroups | gmane.linux.usb.devel |
|---|---|
| Message-ID | <[email protected]> |
On Fri, 16 Feb 2007, Sven Anders wrote: > Some idea I had myself. > Is it possible to use a mix? My idea is as follows: > > Variant 1: > If the completion handler decides, that there is no finger on the touchpad > any more, it does not call usb_submit_urb() again. The completion handler > stops. Via an kernel timer I will call the completion handler to test, if > there is a finger on the touchpad again. If so, I will restart the interrupt > handler and will call usb_submit_urb() until I have no finger on the pad > again. That will work. (Except that a kernel timer routine can't call the completion handler. It will have to resubmit the interrupt URB.) > Variant 2: > If the is no finger on the touchpad, I will make the interval longer until > I have a finger on the pad again... > > For variant 2 I want to know, if it is sufficent to set the 'interval' > variable in the urb struct to a new value or do I have to call a function?! You don't have to call a function; setting the "interval" field is all you need to do. However, you cannot do it in a completion handler. If the completion handler tries to change urb->interval and then calls usb_submit_urb(), it won't work. Either urb->interval will get changed back to its old value or else usb_submit_urb() will return an error. Also you should bear in mind that host controller drivers have upper limits for the interval. For example with uhci-hcd, urb->interval cannot be larger than 128 (and I'm planning to reduce the upper limit to 32). Alan Stern ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel