Date: Tue, 30 Jun 1998 20:47:42 +0200 (SAT) From: John Hay <jhay@mikom.csir.co.za> To: phk@critter.freebsd.dk (Poul-Henning Kamp) Cc: freebsd-smp@FreeBSD.ORG Subject: Re: time problem? Message-ID: <199806301847.UAA19830@zibbi.mikom.csir.co.za> In-Reply-To: <15031.899230982@critter.freebsd.dk> from Poul-Henning Kamp at "Jun 30, 98 08:23:02 pm"
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>
> >I followed Tony Li's advice and started ntpd again on the machine with
> >no local reference clocks and the machine has now been up for more than
> >24 hours with no jumps at all, so it looks like it is calling nanotime()
> >from within the sio interrupt that causes the problems. :-(
>
> yes, that may not be entirely safe to do according to Bruce.
>
> >So what are my options then? Can I somehow run the sio interrupts at
> >a lower priority? I would really prefer to have the pps signal on the
> >serial port, because the port is already used to read the serial stream
> >from the GPS.
>
> I don't know :-)
Hmmm, so it seems that I'll have to get the soldering out and get the
pps signal hooked up to the printer port to see if that works better. :-)
>
> You're entering territory here where I have not yet managed to venture...
>
> I pressume you havn't used the PPS_SYNC stuff in the kernel (if not: don't!)
Well I have and on the old 486 it works pretty ok, so I guess I shouldn't
upgrade it until I have resolved this. :-)
What I do know is the way you calculate the second pararameter for
hardpps() in your printer port pps driver and the way I did it in
my patch, seems to make it very unstable. :-)
Here is how it looks on the 486:
-------------
# /usr/local/sbin/ntpdc shark
ntpdc> kerni
pll offset: 0 us
pll frequency: -14.932 ppm
maximum error: 15266 us
estimated error: 1 us
status: 0107
pll time constant: 2
precision: 1 us
frequency tolerance: 512 ppm
pps frequency: -55.983 ppm
pps stability: 0.010 ppm
pps jitter: 2 us
calibration interval: 256 s
calibration cycles: 6790
jitter exceeded: 450
stability exceeded: 4
calibration errors: 37
ntpdc> peer
remote local st poll reach delay offset disp
=======================================================================
=GPS_NMEA(0) 0.0.0.0 0 64 377 0.00000 -0.000049 0.00092
*PPS(0) 0.0.0.0 0 64 377 0.00000 0.000001 0.00092
+orca.cids.org.z 0.0.0.0 1 64 0 0.00000 0.000000 16.0000
----------------
> And it doesn't happen if you run !SMP with the TSC timecounter, right ?
I'll have a look at it again.
John
--
John Hay -- John.Hay@mikom.csir.co.za
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