[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.
> 




More information about the questions mailing list