[ntp:questions] How do I enable PLL in the Linux kernel?
David Woolley
david at ex.djwhome.demon.co.uk.invalid
Wed May 28 09:00:00 UTC 2008
Anton Persson A wrote:
> The output I get from kerninfo is the following:
>
> ntpdc> kern
> pll offset: 0 s
> pll frequency: 0.000 ppm
> maximum error: 0.414224 s
> estimated error: 1.6e-05 s
> status: 0040 unsync
> pll time constant: 4
> precision: 1e-06 s
> frequency tolerance: 512 ppm
>
> My questions are:
> * What does "0040 unsync" mean?
From /usr/include/sys/timex.h on Linux 2.4:
#define STA_UNSYNC 0x0040 /* clock unsynchronized (rw) */
> * Does this inform me that my
> kernel has NOT been "specially modified for
> a precision timekeeping function."?
No. The system call that provides this information would not have been
present if there was no support.
> * How do I make sure the PLL is enabled?
From miscopt.html in the documentation supplied with ntpd version
4.2.4p4, although possibly omitted by vendors:
enable [ auth | bclient | calibrate | kernel | monitor | ntp | pps |
stats]
disable [ auth | bclient | calibrate | kernel | monitor | ntp |
pps | stats ]
Provides a way to enable or disable various system
options. Flags not mentioned are unaffected. Note
that all of these flags can be controlled remotely
using the ntpdc utility program.
...
kernel
Enables the kernel time discipline, if available.
The default for this flag is enable if support is
available, otherwise disable.
and from ntpdc.html, in the same place:
enable [ auth | bclient | calibrate | kernel | monitor | ntp | pps |
stats]
disable [ auth | bclient | calibrate | kernel | monitor | ntp |
pps | stats]
These commands operate in the same way as the enable
and disable configuration file commands of ntpd. See
the Miscellaneous Options page for further information.
> * Does the PLL feature require special hardware?
We are not talking about a "PLL feature"; ntpd always uses a PLL when
disciplining the clock. We are talking about the kernel feature, where
the PLL runs in the kernel, rather than the ntpd application. Neither
require special hardware.
Generally, I would only expect kerninfo to say unsynced, out of the box,
if more conventional indications of a failure to synchronise (ntpq
peers) were also showing unsynchronised. I'm wondering if you are
looking too deep for a a problem that would better be diagnosed with
ntpq peers and ntpq rv output.
>
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