[time-nuts] BC637PCI 1024 week rollover

GandalfG8 at aol.com GandalfG8 at aol.com
Tue Feb 11 12:09:28 EST 2014

Ah, sorry, when you commented before about modifying the demo software  it 
obviously didn't register with me quite what you were trying to do.
In the BC637PCI Demo software, I'm using version 7.0.0, under the  "Help" 
menu, one item is Receiver Firmware Version and this returns the Packet  45 
If it's any consolation, mine is the same as yours, except for the date  
showing as 4/1/1900:-)
2000 doesn't seem unreasonable for the Ace3 firmware date, my  BC637 
itself, another drop down on that same Help menu, shows as Version  DT10041V12, 
Number 2.21, Date 2/10/2003, which ties in pretty well  with Symmetricom 
completing their takeover of Datum in late 2002  and introducing their BC637PCI-U 
own brand replacement in 2004.
What I do find intriguing though is that your Packet 41 data is returning  
the correct GPS week number and Leap Second offset when there's no antenna  
connected, how the heck does it do that?:-)
In a message dated 11/02/2014 16:36:21 GMT Standard Time, time at patoka.org  

I  figured out why GPS FW information was not available by request. To do  
such requests BC637PCI needs to be in "GPS MODE". If I run the request  
in "Free Run", it return the error code. Here is FW infomation from my  
GPS module:

GPS Packet Menu

1. Request Packet 41 -  Gps Time Packet
2. Request Packet 42 - Gps Position Packet
3. Request Packet 46 - Gps Health Packet
4. Request Packet 45 - Gps  FW
0. Back to main menu

Select:  1


Seconds of Week:  232505.89
GPS Week Number: 1779
GPS/UCT Offset:   16.00

Select: 4


FW: 08-08, 04/01/2000 : 10-16, 04/01/2000

If its correct,  than I have pretty old GPS module. I got my GPS antenna, 
however it has  N-type connector on it. Now I need to find the way to 
connect it to  SMA.



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
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