Date: Fri, 29 Nov 2019 10:55:56 -0700 (MST) From: Ross Alexander <rwa@athabascau.ca> To: Ian Lepore <ian@freebsd.org> Cc: "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: rpi3 clock drift Message-ID: <alpine.BSF.2.21.99999.352.1911291053140.17959@autopsy.pc.athabascau.ca> In-Reply-To: <65be6d3628a8d35084f7c98266582090f59b18be.camel@freebsd.org> References: <alpine.BSF.2.21.99999.352.1911271039470.281@autopsy.pc.athabascau.ca> <MWHPR06MB3134EC22EC3148DA800B2B7DAA440@MWHPR06MB3134.namprd06.prod.outlook.com> <alpine.BSF.2.21.99999.352.1911272214050.28592@autopsy.pc.athabascau.ca> <20191129052800.GA37113@server.rulingia.com> <alpine.BSF.2.21.99999.352.1911282333250.90234@autopsy.pc.athabascau.ca> <65be6d3628a8d35084f7c98266582090f59b18be.camel@freebsd.org>
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On Fri, 29 Nov 2019, Ian Lepore wrote:
> On Thu, 2019-11-28 at 23:51 -0700, Ross Alexander wrote:
>> On Fri, 29 Nov 2019, Peter Jeremy wrote:
>>
>>> [...]
>>
>> BTW, another *significant* source of jitter is the brand and age of
>> the sd/mmc card used. [...]
>
> I'm having a real hard time with this one, conceptually. This is
> exactly what every one of our products at $work does: precision timing
> including ntpd and kernel time tracking UTC(GPS) to within a few nanos.
> We've had products in the field for 15 years still using the original
> sdcard and still hitting the same on-time performance numbers as the
> day they were shipped (tracking UTC(GPS) +-10ns RMS).
This is purely empirical. $WORK machine got jitterier and jitterier.
Copied old SD card onto new SD card (straight dd, not a tar/untar),
problem went away. Beats me, but thats how it went.
regards,
Ross
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Ross Alexander, (780) 675-6823 desk / (780) 689-0749 cell, rwa@athabascau.c=
a
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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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