I set my laptop at the same time I set the system time and the
hardware clock, wich was well over 24 hours ago, and the laptop is
still within 1 second. Also the on-board battery-backed real-time
clock is still within 1 second. Of course these are both at room
temperature. I have come to expect that devices opperating at around
room temperature should maintain in the range of 1 second per day,
maximum 2 seconds drift. That is what I have seen.
Well, I think we have beat this horse to death for now and should move
on. I look forward to improved drift in the future with your Arm
boards. In the mean time, I will use work-arrounds.
On 4/18/06, Jesse Off <> wrote:
>
>
> > Your goal should be Arm boards that are within 1 second per day on
> the
> > system clock. I would imagine, with the hardware you have, you
> could
> > achive that with a little creativity, it is a matter of software.
>
> 1 second per day is beyond what can be done with today's common
> crystal oscillator technology. You would have to go with expensive
> temperature compensated crystal oscillators or rubidium
> oscillators. One may be able to calibrate a single unit at a
> constant temp better than 50 PPM, but crystals also drift with age--
> it would be impossible for a manufacturer of hardware to guarantee a
> more accurate clock than that of the crystal manufacturer and
> crystal manufacturers say 50 PPM.
>
> The timing drift in this instance is excacerbated by software,
> specifically the Linux kernel and its legacy of a 100Hz tick rate.
> We cannot take ownership of all Linux problems just like one cannot
> expect to be able to contact the USB mouse manufacturer when a mouse
> pointer locks up on a PC screen. We fix what we can, but we can't
> get any better accuracy currently with Linux. I believe another one
> of our customers in this forum actually use the TS-7200 in a NTP
> server product they designed-- you may want to contact them for any
> patches they may have made to the kernel.
>
> GPS units have very precise timing. We have a PC104 daughterboard
> designed for a customer that includes a GPS unit that extracts an
> extremely precise 1Hz and 10000Hz signal from the air. This
> solution would still be much cheaper than a rubidium oscillator.
>
> //Jesse Off
>
>
>
>
>
>
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