thoughts on A-GPS offline

mqy meng.qingyou at
Tue Mar 3 15:47:26 CET 2009

I've verified the issue on GPS receiver in GTA02:

When dump ALM/EPH messages, in several messages, fields follow SV ID field
in payload are filled with zeros.

Daniel Willmann wrote:
> On Sun, 1 Mar 2009 14:25:14 -0800 (PST)
> mqy <meng.qingyou at> wrote:
>> "
>> UBX-AID-EPH and UBX-AID-ALM Messages for Satellite without valid
>> Orbits When polling UBX-AID-EPH or UBX-AID-ALM messages, satellites
>> without valid ephemeris or almanac data will 
>> return a complete UBX-AID-EPH or UBX-AID-ALM message with all data
>> words set to zero. This doesn’t comply 
>> with the protocol specification. Furthermore, u-blox 5 receivers with
>> firmware V5.00 and earlier can run into a 
>> floating-point exception when fed with such “empty” ephemeris. 
>> "
>> Is that the cause :D
> Yeah, thought that at first as well, but almanac data was okay at that
> point. The position was not, however. I guess the problem the chip
> tripped over is similar in both cases though.
> Regards,
> Daniel Willmann
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