How to adjust clock frequency in FreeBSD 10.1 ?

[Rick Thomas]

On Feb 11, 2015, at 9:36 PM, Adam Vande More <amvandemore at gmail.com> wrote:

> On Wed, Feb 11, 2015 at 9:09 PM, Rick Thomas <rbthomas at pobox.com> wrote:
> 
>> Hi All,
>> 
>> I’ve got a machine with a really bad clock.  When I run NTP on it, the
>> freq goes straight to 500.0 (over a period of a few days) and stays there,
>> while the offset grows and grows.
>> 
>> I recently switched this machine from Debian Linux to FreeBSD (wanting to
>> learn more about FreeBSD).  Under Linux, I used adjtimex to modify the TICK
>> value and (once I had converged on the right value) NTP was able to
>> stabilize the clock.
>> 
>> Is there an equivalent hack for FreeBSD?
>> 
> 
> You may wish to play around w/
> 
> sysctl kern.timecounter
> 
> to find a setting that works for you.

When I try to change the frequency with (e.g.)
    sysctl kern.timecounter.tc.timebase.frequency=36000000

I get
    sysctl: oid ‘kern.timecounter.tc.timebase.frequency' is read only

Is there some other way to set the frequency?

Thanks!
Rick