[ntp:questions] Issues with ACCORD Reference Clock Driver

David L. Mills mills at udel.edu
Mon Dec 3 20:11:33 UTC 2007


Jason, et al,

You might have noticed the mode subcommand in the refclock command. It 
uses the ttl member in the association data structure and is intended to 
pass stuff like bit rate, etc., to the base driver. If at all posible, 
it would be best if the driver could automatically select the baud rate 
based on unsolicited data from the radio. However, all radios known to 
me, except the NMEA radios, have selectable bit rates.

Over the years and with some effort several drivers now support more 
than one device. All TrueTime models are supported by one driver; all 
Spectracom models by another and all telephone modem services by a 
third. With few exceptions, a NMEA radio is a NMEA radio and I strongly 
suspect many of those drivers could be combined in one driver.

You don't appreciate how tedious the support process is when some 
important thing or other requires a minute change in the common 
interface (nanoseconds unstead of microseconds) and modifications to 46 
files. The urge for utmost KISS and fewest driver files in the public 
distribution is very strong. The problem is that the distribution build 
process is so intricate that few refclock builders, including me, can 
figure out how to incorporate a new driver in a private distribution 
other than as a cuckoo of a current one.

Dave

Jason Rabel wrote:
>>As per your suggestion I would have used the existing NMEA
>>reference clock driver
>>for Accord GPS Clock. But there are certain issues as listed below.
>>
>> 1. Accord GPS Clock spits out NMEA at 9600 baudrate
>> 2. It has custom NMEA format for GPS (and the driver is
>>intended to use this )
>> 3. It also spits out time and status messages in a proprietary
>>binary format (not yet tested...but wll do )
>>
>> So instead of changing the clean NMEA driver to support the above,
>> I still think its better to write and maintain a separate driver.
>>
>> Comments plz...
> 
> 
> #1 above would require changing only 1 line of code from the base NMEA
> driver. I've often wondered why you can't pass the baud rate via the conf
> file. It makes more sense to me to have the software adjust for the GPS,
> rather than having to change the GPS (if possible) to accommodate the
> software.
> 
> #2 above, depending on the format, could require as little as only 1 or 2
> lines of code to be changed / added. At the very worst you might have to
> modify the small chunk of code that searches for the time code in the
> string, still a very minor modification.
> 
> #3 above - Is there any advantage to using the binary format? Is there any
> information that NTP can use that would justify the additional code?
> 
> I've never heard of Accord until you started posting asking questions about
> a driver. Excluding their website, there seems to be no other information on
> the Internet about them (or people using them). I wouldn't exactly call it a
> 'high profile' product.




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