[ntp:questions] Re: Errors with NMEA refclock

John Pettitt jpp at cloudview.com
Mon Jan 30 20:04:05 UTC 2006

Danny Mayer wrote:
> John Pettitt wrote:
>> Danny Mayer wrote:
>>> David J Taylor wrote:
>>>> You are, of course, correct.  However, many devices /do/ allow higher 
>>>> speeds (which would provide lower timekeeping jitter), but there is no 
>>>> easy way to tell ntpd about the higher speed.  I see that flag1 and flag4 
>>>> are unused for this driver, so that might be a way to pass the port number 
>>>> and baud rate under Windows.  E.g. flag4 19200.
>>>> (Perhaps the port number is implied already by the unit number in the 
>>>> address?)
>>>> David 
>>> If the specific baud rate is defined in the spec then we shouldn't be
>>> providing knobs to turn to change it.
>>> Danny
>> Why?  If NMEA devices allow the default to be changed it seems reasonable that the driver should
>> too.  I don't see a downside to allowing the data rate to be changed.
>> John
> That's part of the question that's not clear to me. It's one thing if
> it's only designed for one baud rate, it's something else if the spec
> allows for other baud rates.
> Danny

As has been pointed out other versions of the standard allow for other speeds (38400).  Even if they
didn't many devices can be configured to be non standard compliant running at 9600, 19200 etc - it
seems reasonable to allow a user to break the standard if they choose.  The underlying point of the
standard is to allow multiple nmea devices to inter-operate - since we are only dealing with one
device at a time the issue is somewhat moot.


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