Jan, If no ntp server updates are made to the Linux clock, we have noticed over a week's period a drift of ten or so seconds difference between the Linux clock and the Xenomai get time function and often have to reboot our machine to resynchronize the Xenomai and Linux clocks back to less than a couple seconds difference. I was wondering if you might explain why that might happen?
SIncerely, Joshua Karch ________________________________________ From: xenomai-help-boun...@gna.org [xenomai-help-boun...@gna.org] On Behalf Of Jan Kiszka [jan.kis...@siemens.com] Sent: Monday, May 17, 2010 10:13 AM To: Steve Deiters Cc: xenomai-help@gna.org; Mauerer, Wolfgang; Andreas Glatz Subject: Re: [Xenomai-help] Question about getting system time Steve Deiters wrote: >> Periodically setting the time is risky if timed jobs depend >> on Xenomai's real-time clock - it may jump in all directions... >> >>> Any other suggestions for providing timestamps to real time >> tasks in >>> this case? >> Do you just need precise timestamps from with real-time >> tasks, or do you have to synchronize timer events of the >> Xenomai core on an external clock? >> >> For the former case (precisely our scenario), we laid the >> ground to extend Xenomai 2.5 with RT-safe syscalls to obtain >> Linux's view on gettimeofday. It "just" needs some polishing >> to post this for upstream. >> Wolfgang (CC'ed) is working on this. > > I'm just looking to get timestamps in the real time task. At least in > my case being able to call gettimeofday from the real time thread would > be exactly what I need. > > By the way, calling gettimeofday currently within a real time thread > seems to occasionally freeze up my whole system. I was going to make > another post for this after I got a chance to verify some details. Has > anyone noticed anything similar to this? > Yes, that's expected: If gettimeofday runs syscall-less, it tries to read the time offset from a page which the Linux kernel updates regularly. When user-space detects an ongoing update, it spins until that has completed. But as Xenomai runs the task with higher priority than the Linux update handler, you just ran into a live-lock. Switching on the Xenomai watchdog will confirm this: It will shoot that task, and the system will recover. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux _______________________________________________ Xenomai-help mailing list Xenomai-help@gna.org https://mail.gna.org/listinfo/xenomai-help _______________________________________________ Xenomai-help mailing list Xenomai-help@gna.org https://mail.gna.org/listinfo/xenomai-help
