On Sat, 2007-03-03 at 11:44 +0100, Laurent Pinchart wrote: > I'm trying to find a way to synchronise the Linux system clock with a device > clock using the USB frame counter as a shared clock.
In a related scenario I have an USB device that periodically sends its device clock over USB and I wanted to relate that clock to the system clock. I did it without involving the USB frame clock, however (maybe you can reduce the jitter of the time measurements if you do). I modelled the relationships of the device clock (y) to the system clock (x) as a linear one: y =~ ax+b Whenever the device sends its device clock value, I obtain a system clock sample and process it as a pair (x_i, y_i). >From multiple of these pairs, you can then compute estimates for a and b, eg. using a least-squares criterion. I ended up doing recursive least squares with a forgetting factor. I.e. the estimates for a and b are updated whenever a new measurement (x_i, y_i) arrives. >From the estimates a and b you can convert time instants between the two clocks. There's lots of documentation on RLS if you google on the web, eg. http://www.cs.tut.fi/~tabus/course/ASP/LectureNew10.pdf Tom ------------------------------------------------------------------------- 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 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
