RE: [uCsimm] For exact date

From: Stu (
Date: Fri Mar 10 2000 - 02:46:32 EST

This may be stating the obvious, but it does bear stating... For purposes of
normal uClinux and especially RTLinux, it might be useful to build a more
accurate high-res timer circuit and have it take one of the SIMM's IO pins
high once per a set interval (say, 1 second, 1 minute, 5 minutes, whatever
suits the application the SIMM is being used for). The kernel could catch
this and compare it against the system clock, correcting for drift. I can't
imagine such a circuit would cost very much, and it would almost certainly
fit on even a small portion of the gardener breadboard.

Of course, NTP is better than this, but obviously there are some
applications where no network connectivity or limited network connectivity
would be available.

> -----Original Message-----
> From: []On
> Behalf Of 권석근
> Sent: Thursday, March 09, 2000 6:33 PM
> To:
> Subject: Re: [uCsimm] For exact date
> Hi, Larry
> >It is whatever the crystal is. You can buy both 32.768 and 32.000 kHz
> >crystals, and the DragonBall can't tell the difference. Of course,
> >whichever crystal you buy has about a 100 ppm error budget (initial set,
> >temperature coefficient, aging).
> >
> >Real Linux kernels can phase slip their internal UTC clock to the
> >external timebase at an arbitrary rate, settable to a fraction of a ppm.
> >I hope RTLinux can do that too.
> >
> You mean time correction code (11 minite interval) of linux
> kernel? or NTP?
> Real Linux kernel means Normal Linux kernel?
> I've heard that normal destop has seperated RTC chip and they say it uses
> cheap crystal. Therefore linux kernel has correction code for
> this RTC using
> system clock (they say it more accurate than RTC crystal).
> If what you mentioned was about this, then we do not need this support,
> in my thought. Because EZ328 shares same cystal for RTC and system
> clock, this correction code could be meaningless.
> BTW, david william's idea about reverse(?) correction code from RTC to
> system clock was great. In sleep/doze mode (for battery operation),
> the only clock running would be CLK32. another idea?
> My uCsimm shows correct time after 12 hours, and system date
> might be considered as having crystal resolution.
> Thanks.
> kwonsk.
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