[time-nuts] BC637PCI 1024 week rollover

[Magnus Danielson]

On 09/02/14 23:24, d0ct0r wrote:
>
> 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.]

First GPS week of 2016 is GPS week of 1878.

Which gives indication wrap-around and also means it has been valid 
since mid 1996.

> [ 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]

If you don't listen to the Extended GPS Week Number, you are toast, but 
as there is an end to the Ace III extension capability, there isn't far 
away and you are toast anyway.

> ====================================================
>
> 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.

I think this is another case where the developers didn't forsee this 
situation.

Cheers,
Magnus