[time-nuts] BC637PCI 1024 week rollover

d0ct0r time at patoka.org
Tue Feb 11 12:35:54 EST 2014


Sorry for confusing information. I have some small Trimble antenna which 
currently connected to BC637PCI. However I never get it "locked" with 
that antenna:

GPS PACKET 46 - GPS HEALTH PACKET
Status: No usable satellites
Error: 63

Binary Time: 02/11/2014  17:28:40.0572284   Status: 7
Binary Time: 02/11/2014  17:28:40.0672927   Status: 7
Binary Time: 02/11/2014  17:28:40.0773571   Status: 7

Notice "Status: 7". Ideally it should be "Status: 0". As far as I 
understood from the documentation, if GPS is not locked then BC637PCI 
will using its "freerun mode".

My board FW even older. Its DT10041V11.

Since I am using this card for my "home-brewed" Startum 1 NTP server, I 
am thinking to connect to BC637PCI some external 10MHZ GPSDO to keep it 
in sync and not using the GPS part at all. The card itself doing well if 
its in "free run" mode.

Regards,
V.P.


On 2014-02-11 12:09, GandalfG8 at aol.com wrote:
> 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
> data.
> 
> 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?:-)
> 
> Regards
> 
> Nigel
> GM8PZR
> 
> 
> 
> In a message dated 11/02/2014 16:36:21 GMT Standard Time, 
> time at patoka.org
> writes:
> 
> 
> 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
> 
> GPS PACKET 41 - GPS TIME PACKET
> 
> Seconds of Week:  232505.89
> GPS Week Number: 1779
> GPS/UCT Offset:   16.00
> 
> Select: 4
> 
> GPS PACKET 45 - GPS  FW
> 
> 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.
> 
> Regards,
> 
> V.P.
> 
> 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.
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-- 
WBW,

V.P.



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