On Thu, 2011-01-20 at 02:15 -0800, Hal Murray wrote: > > What is the accuracy of the hwclock on XOs? Can we assume that it will keep > > good time over an XO's five-year lifespan? > > The ballpark for the hardware is 1 second per day. > > > We have some XO-1.5s that have their hwclocks off by 10-20 minutes. Would > > this likely be due to a fault at the factory (e.g. not setting the time > > before shipping them), or did they skew over time? > > How long ago did you last set the clock? > > Timekeeping is more complicated than that. > > /etc/init.d/halt calls /sbin/hwclock --systohc > So each time you shut down cleanly, your hwclock gets updated with the > current system time. That's probably a good idea if you are running ntpd > like most Linux boxes. >
The main problem is /etc/adjtime doesn't keep it's data used to track whether the rtc is in localtime or utc time, the readonly filesystem layout resets this file on reboot. https://dev.laptop.org.au/issues/299 http://dev.laptop.org/ticket/10605 > However, if you aren't running ntpd (or somehow keeping the system clock > reasonably sane), you are swapping the drift on the hwclock for the drift of > the system clock. > With my observations I'd used the rtc as the source, as the system is drifting over a 1 min per hour. > Sometime in the past few years, the timekeeping corner of the kernel was > cleaned up. Unfortunately, they introduced a bug in the TSC clock > calibration code. > > The main problem for most Linux users is that it doesn't get the same answer > each time it boots. It's close, but not very good if you are interested in > timekeeping. > > If it were consistent, ntpd could easily correct for the error. That's what > /var/lib/ntp/drift is for. (Small variations are expected due to > temperature.) > The would be great to use but a ntp client is not installed by default. > The secondary problem is that it's likely to be off by 10s of seconds per > day. I'll dig out some numbers if anybody wants more details. > > I don't have good data on how well clocks work when power-saving is enabled. > You might be on to something there, on one XO-1.5 with uptime of 12 hours (inactive, I was sleeping), the system clock is now out over 3 hours in that time frame while the rtc is accurate. Well it's not out 3 hours... ;) > ------------- > > If you actually want to know how accurate your hwclock is: > comment out the line in /etc/init.d/halt, > reboot, > check the time, > wait a week or 10 days, > check again. > "ntpdate -d <handy-server>" may be the simplest way to check the time. Grab > ntpdate from a handy system. > Or run "xclock -analog -update 1" on a system running ntpd and use that to > calibrate your wrist watch and ... Going down that route chasing this, Jerry _______________________________________________ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel