Date: Fri, 29 Nov 2019 18:06:59 +0000 From: James Shuriff <james@opentech.cc> To: Ross Alexander <rwa@athabascau.ca>, Ian Lepore <ian@freebsd.org>, "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: RE: rpi3 clock drift Message-ID: <MWHPR06MB313445553D73F019FEEAF50EAA460@MWHPR06MB3134.namprd06.prod.outlook.com> In-Reply-To: <alpine.BSF.2.21.99999.352.1911291053140.17959@autopsy.pc.athabascau.ca> 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> <alpine.BSF.2.21.99999.352.1911291053140.17959@autopsy.pc.athabascau.ca>
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Can you help me determine where the timecounter frequency is being pulled f=
rom? I believe that 54 MHz value is being pulled from the FDT I just don't =
know where specifically. My board is supposed to be 19.2 MHz. I booted up F=
reeBSD's own RPI3 image and I got 19.2 MHz and didn't have any drift issues=
. Only when I use the environment I built from source do I get 54 MHz, as i=
f an RPI 4 DTB somehow made it into the build.
I'm also interested in getting an RTC hat. I know how to build support for =
it in the bootloader and OS but how do you tell FreeBSD to start using it f=
or system timing once it's connected?
- James Shuriff
-----Original Message-----
From: owner-freebsd-arm@freebsd.org <owner-freebsd-arm@freebsd.org> On Beha=
lf Of Ross Alexander
Sent: Friday, November 29, 2019 12:56 PM
To: Ian Lepore <ian@freebsd.org>
Cc: freebsd-arm@freebsd.org
Subject: Re: rpi3 clock drift
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 n=
anos.
> 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
=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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