[time-nuts] BC637PCI 1024 week rollover

[d0ct0r]

I found the document about Trimble ACE3 module:

http://www.symres.com/files/ACE3.pdf

Here is the paragraph about WNRO:

====================================================
Effect of GPS Week Number Roll-over (WNRO)

The ACE III GPS module has been designed to handle WNRO, and there are 
no problems
with either dates or first fix after WNRO through the year 2015.

[* Note – GPS Week Numbers system, as defined by the ICD200 GPS 
Specification, occupy
a range from zero to 1023. The Week Number Roll Over (WNRO) occurs every 
1024
weeks, or approximately every 19 years 8 months. August 1999 was the 
first roll-over for
the GPS system since the beginning of GPS time on 06 January 1980.]

[ Caution – Trimble OEM GPS receivers have reported the true GPS Week 
Number in TSIP
messages 0x41 and 0x8F-20 as a number between 0 and 1023. The ACE III 
GPS outputs
the Extended GPS Week Number as the absolute number of weeks since the 
beginning of
GPS time or 06 January 1980. If the true GPS Week Number is desired, the 
system
developer should ignore the extra MSBs of the Extended GPS Week Number 
and use only
the 10 LSBs]
====================================================

I tried to modify the "demo" code to obtain FW of my GPS module. But I 
had no luck with it, since
"bcGPSMan" subroutine always return ERROR state in response to packet ID 
0x1F.


Regards,

V.P.

On 2014-02-09 16:05, GandalfG8 at aol.com wrote:
> In a message dated 09/02/2014 15:31:47 GMT Standard Time,
> magnus at rubidium.dyndns.org writes:
> 
> On  09/02/14 12:56, GandalfG8 at aol.com wrote:
>> Oh well, full credit to Mr  Trimble for getting it right, he does bake
>> exceedingly nice GPS  modules and the Ace3 doesn't have a rollover 
>> issue
> and it
>> does  report the date correctly.
>> 
>> Unfortunately, as far as I can tell  anyway, the BC637PCI takes the 
>> raw
> GPS
>> time data from the Ace3 and  performs its own calculation which is 
>> where
> the
>>   problem  seems to occur, certainly it's a 1024 week issue with the 
>> date
>>  from  the BC637 being displayed as June 26 1994 in all versions of  
>> the
>> associated  demo software.
>> It is possible to set the  date correctly but the next packet from the 
>> GPS
>> module promptly  overwrites it again.
>> 
>> I still don't recall seeing this before,  although with two boards
> behaving
>> in the same fashion I'm having  doubts about that, but more to the 
>> point
>> these boards indicate a  firmware date of 2003 which implies they were
> put
>> into the field  like this, and that doesn't make much sense  either.
>> 
>> Any  ideas anyone?, and again has anyone else seen this and/or am I
> missing
>>  something glaringly obvious?
> 
> If the ACE3 gives correct date, but the  BC637 FW does not, then it is
> obvious that the FW does the unwrapping  itself just like a problematic
> GPS receiver would. Most probably would the  ACE3 have issues if it
> looses it's CMOS backup.
> 
> I haven't looked at  those details, but you should be able to disable 
> the
> date from being set  by the GPS. Maybe play around there.
> 
> Might be that the FW needs an  update, which naturally may not be in
> existence. Can you read-out the  EPROM?
> 
> Only proves to show that my comment that NTPD needs to do the  1024 
> week
> correction for other GPS dependent drivers than the NMEA (NTP  bug 
> 2466)
> is a correct assumption. See the posting I forwarded  yesterday.
> 
> Cheers,
> Magnus
> Hi Magnus, and thanks for your comments.
> 
> I arrived at the same conclusion regarding the BC637 firmware and  
> that's
> the issue I'd like to resolve, but I'm a bit cautious given that these  
> were
> produced after 1999 as I can't understand why the firmware wouldn't 
> already
> have been updated.
> 
> It is possible to set the board for other than GPS, (Timecode, 
> Freerunning,
>  or 1PPS) but I suspect I might then loose the conditioning, something 
> I'd
> need to check. Either way, I'd like to have the correct GPS date too if
> possible, but it's the conditioning that's of more interest so I'd do 
> without
> the correct date if needs be.
> 
> I've identified two programmable devices, the version H manual  with
> schematics is very useful:-), the first being a OTP configuration PROM  
> for the
> Spartan FPGA and the other a TMS29F010 flash mamory IC which I suspect  
> holds
> the firmware. That is socketed but I don't think I have the necessary 
> 32
> pin quad adapter to be able to read it.
> 
> This was only intended to be a quick test, funny how "quick  tests" 
> soon
> become major projects:-), so these might have to go back  into 
> hibernation
> again shortly, for the time being at least.
> 
> Regards
> 
> Nigel
> 
> 
> 
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-- 
WBW,

V.P.