From: Richard Cochran <richardcochran@gmail.com>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Vladimir Oltean <olteanv@gmail.com>, netdev@vger.kernel.org
Subject: Re: phc2sys - does it work?
Date: Mon, 27 Jul 2020 07:10:15 -0700 [thread overview]
Message-ID: <20200727141015.GA16836@hoboy> (raw)
In-Reply-To: <20200726212952.GF1551@shell.armlinux.org.uk>
On Sun, Jul 26, 2020 at 10:29:53PM +0100, Russell King - ARM Linux admin wrote:
> I have noticed that phc2sys can sometimes get confused and it needs
> phc_ctl to reset the frequency back to zero for it to have another go.
> The hardware is capable of a max_adj of S32_MAX, and I think that
> allows phc2sys to get confused sometimes, so I probably need to clamp
> my calculated max_adj to a sane limit. Is there an upper limit that
> phc2sys expects?
The program uses the minumum of the PHC's max_adj and the
max_frequency configuration value (whose default is 900000000).
In general, huge frequency corrections are a sign that something is
wrong. If your setup has sudden phase jumps (like ntpd resetting the
clock), then you should consider allowing phc2sys to jump as well.
For example, I use
phc2sys -S 0.128
which allows phc2sys to jump when the offset is greater that 128
milliseconds. That value is chosen to match ntpd's threshold for
jumping the time.
HTH,
Richard
next prev parent reply other threads:[~2020-07-27 14:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-25 12:49 phc2sys - does it work? Russell King - ARM Linux admin
2020-07-25 13:29 ` Vladimir Oltean
2020-07-26 11:01 ` Russell King - ARM Linux admin
2020-07-26 18:05 ` Richard Cochran
2020-07-26 21:29 ` Russell King - ARM Linux admin
2020-07-27 14:10 ` Richard Cochran [this message]
2020-07-26 19:53 ` Vladimir Oltean
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