[time-nuts] BC637PCI 1024 week rollover

d0ct0r time at patoka.org
Thu Feb 13 16:53:49 EST 2014


I modified two things for now. Its a "demo" software (Linux edition). 
And refclock_banncom driver for NTP. Personally, I would prefer to 
modify microcode or library. But that is proprietary with no source code 
around.

Regards,
V.P.

On 2014-02-13 10:46, GandalfG8 at aol.com wrote:
> You've lost me, what code are you modifying at the moment, is it the
> actual Datum demo software?
> 
> Regards
> 
> Nigel
> GM8PZR
> 
> 
> In a message dated 12/02/2014 03:48:12 GMT Standard Time, 
> time at patoka.org
> writes:
> 
> 
> You  are right ! Now I am going to modify the code a lit bit.
> 
> Each time as  we call bcReadBinTimeEx or bcReadBinTime, we need to add
> "magic number" to  unsigned long pointer which store major time. 
> Example:
> 
> if  (bcReadBinTime(stfp_handle, &btm[1], &btm[0], &stat ) == 0)  {
> msyslog(LOG_ERR,  "get_datumtime error:
> %m");
> return(NULL);
> }
> btm[1] + 619315200;
> 
> 
> At least  its working for "demo":
> 
> Binary Time: 02/12/2014   03:45:09.6158902   Status: 7
> Binary Time: 02/12/2014   03:45:09.6259547   Status: 7
> Binary Time: 02/12/2014   03:45:09.6360200   Status: 7
> 
> 
> 
> 
> On 2014-02-10 18:51,  GandalfG8 at aol.com wrote:
>> In a message dated 10/02/2014 21:56:25 GMT  Standard Time,
>> magnus at rubidium.dyndns.org writes:
>> 
>>  On  10/02/14 11:15, GandalfG8 at aol.com wrote:
>>> Ah, I took 1999  as I thought  that was the only relevant date for
>>>  another
>>> 1024 weeks, I'm not  familiar with the shifted 1024  week period so
>>> will
>> take a
>>>    look  at that.
>>> 
>>> Does "shifted" imply a shift at the whim of  the  manufacturer, ie
>>> could
>> it
>>>  explain why these boards might have  been ok a few years  ago but  
>>> not
>>> now?
>> 
>> Yes. We have seen week 500  and  week 512 occuring.
>> 
>> Considering this simple code:
>> 
>> if (gpsweek  < 500)
>> gpsweek += 1024;
>> 
>>  This means that GPS week  500 to 1023 maps straight and truncated  
>> GPS
>> week 0 to 499 is mapped to GPS  week 1024 to 1523.
>> 
>> However, when GPS week 1524 occurs, GPS week 500 is   transmitted, so
>> receivers jump from GPS week 1523 to GPS week 500 and  the  NMEA 
>> readout
>> date jumps 19.3 years. Woops.
>> 
>>  The interesting thing is  that the GPS otherwise operate properly, as
>> it
>> is only the read-out date  which goes wrong, not the  internal gears 
>> of
>> the GPS, so the leap second  applied will be  the current and not the
>> one
>> from 19 years  ago.
>>  -------------------------------------
>> Yes, that's what I was seeing,  anything received by the GPS module 
>> was
>> passed through correctly, week  number, leap seconds, etc, it was what
>> the BC637
>>  did  with it after that wasn't quite so helpful.
>>  -------------------------------------
>> 
>> 
>> 
>>>  Oh dear, I think a wee light bulb has just  exploded:-)
>> 
>>  Good. :)
>> 
>>> I haven't checked this yet, but if   shifting means to  start a 1024
>>> week
>>> period  that's approximately  from or not too  far before the date  
>>> of
>>> manufacture, either for  individual units or just as   a ballpark for 
>>> a
>> given production
>>>  run, that would  buy them nearly twenty  years from then, which 
>>> would
>>  mean
>>> these boards should still be ok.
>> 
>> It's  arbitrary. It could  be from writing the code to just before a
>>  certain batch. Who knows.  Adjusting it is trivial.
>> 
>>>  If shifting means to do this say at the  design stage or starting 
>>> with
>>> the
>>> first production run then they might  buy  twenty years from then but
>>> regardless of individual  manufacturing  date.
>> 
>> It's arbitrary. Considering that  GPS week 500 and GPS week 512  have
>> been
>> found in  equipment, and these are not "random numbers", it seems  
>> like
>>  a
>> random pick early in the design.
>> 
>>> I'm not too  sure that  even the earliest of these boards should be
>>>  twenty
>>> years old yet, but  if plan Z was to stick with some  previously 
>>> picked
>>> arbitrary   date, such as company  formation or granny's birthday, 
>>> then
>> that might
>>>  well  be  the answer:-)
>>> 
>>> Thank you, will definitely  look  more closely at this, perhaps it's
>>> not
>>  time
>>>   yet to put the  boards back into hibernation  after all:-)
>> 
>> Good, now you learned  something.  :)
>> ------------------------
>> Certainly seems that way, perhaps  the old brain cell does  still fire
>> up
>> now and again  after all:-)
>> 
>> I was quite surprised though just how little a  Google search threw up
>> on
>> 1024 week offsets, however I worded  it I got plenty of hits regarding
>> the
>> 1024  week  rollover itself, plus its implications, but virtually
>> nothing
>>  regarding the use of offsets and any consequences of that.
>>  -----------------------
>> 
>> 
>> 
>> 
>> 
>>> I agree re the TMS29F010, and I'm sure I could read  it, but  would
>>> definitely need an adapter for that.
>> 
>>  Ah.  Yes.
>> 
>> I don't know what FW my boards have, if it has  the GPS FW latent  or
>> not.
>>  ----------------------------
>> I bought a set of PLCC adapters on Ebay  this afternoon, probably 
>> about
>> time
>>  my programmers  joined the 19th century, so with a bit of luck, a
>>  following
>>  wind, and a good head of steam, I might even have a  dump of the
>> firmware
>> by the weekend:-)
>> 
>>  Regards
>> 
>> Nigel
>> GM8PZR
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> 
> --
> WBW,
> 
> V.P.
> 
> --
> WBW,
> 
> V.P.
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-- 
WBW,

V.P.



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