Date: Wed, 27 Nov 2019 10:59:27 -0700 (MST) From: Ross Alexander <rwa@athabascau.ca> To: freebsd-arm@freebsd.org Subject: re: rpi3 clock drift Message-ID: <alpine.BSF.2.21.99999.352.1911271039470.281@autopsy.pc.athabascau.ca>
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On Wed, 27 Nov 2019, IanLepore wrote:
> Date: Tue, 26 Nov 2019 15:48:54 -0700
> From: Ian Lepore <ian@freebsd.org>
> To: James Shuriff <james@opentech.cc>, Bakul Shah
> <bakul@bitblocks.com>
> Cc: "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org>
> Subject: Re: rpi3 clock drift
> Message-ID:
> <486c0bc46deeefb8338f50fe6dfdf7951786e56c.camel@freebsd.org>
> Content-Type: text/plain; charset=3D"UTF-8"
>
> On Tue, 2019-11-26 at 22:34 +0000, James Shuriff wrote:
>> kern.timecounter.tc.ARM MPCore Timecounter.frequency: 54000000
>
> 54 MHz seems like a very strange frequency for a clock in an arm
> system. Of course, everything about an RPi seems to be strange and
> non-standard.
>
> Can someone else with an rpi3 (which keeps good time) confirm that
> that's the usual number?
>
> -- Ian
Mine does reasonably well; it's disciplined to a local stratum-0 (a
pi2 with a GPS hat supplying PPS). The timecounter values are
rpi3:/var/db/ntp # sysctl kern.timecounter
kern.timecounter.fast_gettime: 1
kern.timecounter.tick: 1
kern.timecounter.choice: ARM MPCore Timecounter(1000) dummy(-1000000)
kern.timecounter.hardware: ARM MPCore Timecounter
kern.timecounter.alloweddeviation: 5
kern.timecounter.timehands_count: 2
kern.timecounter.stepwarnings: 0
kern.timecounter.tc.ARM MPCore Timecounter.quality: 1000
kern.timecounter.tc.ARM MPCore Timecounter.frequency: 19200000
kern.timecounter.tc.ARM MPCore Timecounter.counter: 1547324379
kern.timecounter.tc.ARM MPCore Timecounter.mask: 4294967295
and the ntpq info looks like
rpi3:/var/db/ntp # ntpq
ntpq> lpee
remote refid st t when poll reach delay offset =
jitter
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
*debian2.bogons .PPS. 1 u 39 512 377 0.759 5.328=
3.179
ntpq> rl &1
associd=3D63559 status=3D961a conf, reach, sel_sys.peer, 1 event, sys_=
peer,
srcadr=3Ddebian2.bogons, srcport=3D123, dstadr=3D192.168.2.6, dstport=
=3D123,
leap=3D00, stratum=3D1, precision=3D-19, rootdelay=3D0.000, rootdisp=
=3D1.099,
refid=3DPPS, reftime=3De18933b7.00541adb Wed, Nov 27 2019 10:41:11.00=
1,
rec=3De18933be.acaf7c6a Wed, Nov 27 2019 10:41:18.674, reach=3D377,
unreach=3D0, hmode=3D3, pmode=3D4, hpoll=3D9, ppoll=3D9, headway=3D17,=
flash=3D00 ok,
keyid=3D0, offset=3D5.328, delay=3D0.759, dispersion=3D14.153, jitter=
=3D3.179,
xleave=3D5.695,
filtdelay=3D 0.87 0.76 0.78 0.77 0.79 0.79 0.71 =
0.80,
filtoffset=3D 6.01 5.33 4.48 3.45 2.52 1.53 0.75 =
0.56,
filtdisp=3D 0.00 7.95 16.10 23.85 31.71 39.74 47.61 =
55.62
ntpq> rl
associd=3D0 status=3D0618 leap_none, sync_ntp, 1 event, no_sys_peer,
version=3D"ntpd 4.2.8p12-a (1)", processor=3D"arm64",
system=3D"FreeBSD/13.0-CURRENT", leap=3D00, stratum=3D2, precision=3D-=
21,
rootdelay=3D0.759, rootdisp=3D23.748, refid=3D192.168.2.3,
reftime=3De18931ac.ad6bd044 Wed, Nov 27 2019 10:32:28.677,
clock=3De18933ef.81828f21 Wed, Nov 27 2019 10:42:07.505, peer=3D63559=
, tc=3D9,
mintc=3D3, offset=3D5.327665, frequency=3D-7.309, sys_jitter=3D0.00000=
0,
clk_jitter=3D1.121, clk_wander=3D0.013, tai=3D37, leapsec=3D2017010100=
00,
expire=3D201912280000
ntpq> quit
This box is drifting a bit right now because I've got a 'make -j 3
buildworld' running; the cheapo little resonators that the Pi folks
use instead of crystals drift madly with thermal stress. I can see
the house furnace cutting in and out by graphing the loopstats file
:). While idle it's usually good to less than half a millisecond.
regards,
Ross
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D
Ross Alexander, (780) 675-6823 desk / (780) 689-0749 cell, rwa@athabascau.c=
a
54.71593 N 113.30835 W
Order is simply a thin, perilous condition
we try to impose on the basic reality of chaos.
-- William Gaddis, _J R_
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