[ntp:questions] nmea and initial large offset

Rob nomail at example.com
Fri May 7 19:28:46 UTC 2010


Andy Helten <andy.helten at dot21rts.com> wrote:
>
> Rob wrote:
>> Kalle Pokki <kalle.pokki at iki.fi> wrote:
>>   
>>> Yes, but reference clock drivers don't use the ntp timestamp. Take a
>>> look at e.g. the SHM driver. There
>>>     
>>
>> Is this piece of code something that our friend does not want to change
>> because he believes it is doing the right thing?  Or is it merely badly
>> written by a contributor and nobody got around to cleaning it up?
>>
>> I would say it is completely pointless to decompose a timeval timestamp
>> into separate fields and then back.  That only costs CPU time and induces
>> errors.
>
> You should read the discussion in the bug report that was previously 
> provided by Kalle:  https://bugs.ntp.org/417
>
> It includes justification from David Mills on why it works this way.  I 
> don't know that his justification specifically addressed the inability 
> to even force a quick sync with a refclock when it differs by more than 
> 4 hours from system time (i.e. the CLOSETIME stuff).  To me, there is no 
> justification for such behavior with respect to forcing a quick sync.  
> In such cases, ntpd is saying to the user "I know best" but it turns 
> that it doesn't.

It sometimes gets a bit tiresome that mr. Mills always brings up his
experiences with 20 year old systems to dictate what can be done with
ntpd today.  He has seen clockchips (interestingly named TOY clocks by
him) that don't provide the year, and hence the year should not be
used by anything.  He has a clockdriver that does not provide the year
and so no clockdriver should provide the year.
But is this still true today?  I think any reasonable clock chip in use
today has the year information, and a reference clock like ntpshm has
year info within the range of 32bit time_t just as well.  By the time
that will be a problem, time_t will be 64bit I hope.
We should not drive current users to despair (because they cannot set
their clocks) just because of some problem that existed 20 years ago
or will come up in 28 years time.

With such an attitude against change, it often surprises me that there
hasn't been a major fork of ntpd yet.




More information about the questions mailing list