On Mon, 16 Apr 2007, Greg KH wrote: > On Mon, Apr 16, 2007 at 03:55:50PM -0400, Alan Stern wrote: > > From: Danny Budik <[EMAIL PROTECTED]> > > > > This patch (as899) adds a new ioctl to usbfs: USBDEVFS_GETFRAMENUM. > > It allows user programs to obtain the current Start-Of-Frame number on > > a USB bus. > > But who needs this?
Danny does, for one. So does Laurent Pinchart. See the linux-usb-devel archives for April 13. > > Note that the values returned by the get_frame method in the various > > host controller drivers are not consistent. > > As this number is not consistent, why would exporting it be useful? Well, we can always _make_ it consistent. :-) Besides, even if the exported value doesn't include all 11 bits of the frame number, having even 8 of them might be useful. > > They should be adjusted > > so that they provide the actual frame number as it appears on the bus; > > that is, a number incrementing by one every millisecond, ranging from 0 > > to 2047. That will have to be done separately; it interacts with the > > start_frame values used for submitting Isochronous URBs. > > So the current usb_get_current_frame_number() function isn't really > working properly for the 1 in-kernel user today (the other 3 usages are > just in debug printks)? I don't know if it's working properly or not, although I imagine the maintainers of the HiSax driver might complain if it wasn't doing what they need. There's no question that it will become more important in the future, as people start bringing more stringent requirements for their Isochronous applications. It's an area in which Linux's USB support has traditionally been rather weak, especially for high speed. We have already begun with some protracted discussions between Dave, Monty, and myself about this. Rationalizing the usages of the frame number values seems like a logical next step. Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
