thoughts on A-GPS offline

mqy meng.qingyou at gmail.com
Sun Feb 22 13:10:25 CET 2009


Yes, ogpsd within frameworkd saves/loads u-blox AID HUI/ALM/EPH messages.
u-blox A-GPS online messages are of AID message types. Let's read the html
content dumped from ghex:



> b5 62 0b 01 30 00 2d 26 29 f3 ba ca 13 1a ec b7 6b 18 20 a1 07 00 00 00 ee
> 05 c4 7a 67 0e 00 00
> 
> 00 00 f4 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 03 00 00 00 e8 ce b5
> 62 0b 31 68 00 03 00
> 
> 00 00 80 59 4d 00 00 91 7b 00 51 1b 68 00 06 8a 7e 00 cd 3c 55 00 f7 fb b4
> ff c4 3b 3c 00 2e 00
> 
> 00 00 3b 09 2e 00 d9 fc 3c 00 0e 2e 37 00 9c 27 f2 ff 05 3d fd ff bc 6c f6
> ff a1 db 1c 00 8f f7
> 
> 0d 00 7f c4 3b 00 0d c9 ff ff 33 17 41 00 25 59 00 00 22 32 c1 ff 24 44 0c
> 00 e5 50 46 00 16 a4
> 
> ff ff 33 06 3c 00 e2 f7 b5 62 0b 31 68 00 06 00 00 00 80 59 4d 00 00 90 7b
> 00 51 1b 60 00 06 8a
> 
> 7e 00 cd 3c 55 00 f6 fb b4 ff c4 3b 20 00 82 ff 00 00 10 12 08 00 0b fe 20
> 00 75 5d 34 00 c2 12
> 
> ae ff 02 fb fd ff 4e 22 ec ff a1 0e 1d 00 79 ca 0d 00 7c c4 3b 00 0f 3c 00
> 00 d4 c1 f8 ff 26 f8
> 
> ff ff dc 30 0f 00 c4 df 0b 00 e7 c0 95 ff 0c a8 ff ff 3b 0b 20 00 2b 9d b5
> 62 0b 31 68 00 19 00
> 
> 00 00 80 59 4d 00 00 92 7b 00 51 1b 70 00 06 8a 7e 00 cd 3c 55 00 f0 fb b4
> ff c4 3b 6b 00 db 00
> 
> 00 00 1f a6 1e 00 ff 0c 6b 00 8a bb 31 00 cc bd ea ff 06 1a 0b 00 88 76 0a
> 00 a1 9b 07 00 27 59
> 
> 0d 00 7f c4 3b 00 b8 39 00 00 22 17 98 ff 27 12 00 00 c8 d0 70 00 cd 13 27
> 00 b7 86 fa ff 77 a6
> 
> ff ff eb 11 6b 00 9e ee b5 62 0b 31 68 00 13 00 00 00 00 f1 4d 00 00 90 7b
> 00 51 1b 60 00 06 8a
> 
> 7e 00 cd 3c 55 00 e1 fb b4 ff c3 3b 0c 00 fb ff 00 00 46 46 04 00 57 00 0c
> 00 29 41 2f 00 48 c4
> 
> d7 ff 02 49 00 00 75 0b a2 ff a1 b9 1c 00 3a 5d 0e 00 1c c3 3b 00 14 3d 00
> 00 cb 85 b9 ff 27 17
> 
> 00 00 68 fa 05 00 f0 fa 0d 00 07 56 28 00 c0 a9 ff ff 59 10 0c 00 30 ab b5
> 62 0b 31 68 00 0d 00
> 
> 00 00 80 59 4d 00 00 90 7b 00 51 1b 60 00 06 8a 7e 00 cd 3c 55 00 e8 fb b4
> ff c4 3b 29 00 0b 00
> 
> 00 00 c8 c3 25 00 b1 09 29 00 39 9f 24 00 00 9d 3e 00 01 0f 08 00 65 c0 ed
> ff a1 85 1d 00 a4 18
> 
> 0e 00 7c c4 3b 00 94 e8 ff ff d3 5b 00 00 28 d7 ff ff 20 85 8f ff 3d 86 0f
> 00 60 1c 5a 00 25 ae
> 
> ff ff 94 01 29 00 0d b3 b5 62 0b 31 68 00 10 00 00 00 80 59 4d 00 00 90 7b
> 00 51 1b 60 00 06 8a
> 
> 7e 00 cd 3c 55 00 eb fb b4 ff c4 3b 1d 00 e7 ff 00 00 cd e8 09 00 9d f1 1d
> 00 74 3a 31 00 84 6b
> 
> 89 ff 02 a4 f3 ff 15 cc 98 ff a1 fa 0c 00 94 1a 0e 00 63 c4 3b 00 e7 d7 ff
> ff 4a a6 fe ff 27 3a
> 
> 00 00 19 e8 6d 00 f0 d2 20 00 cc 99 42 00 53 a6 ff ff 6f ee 1d 00 be a9 b5
> 62 0b 31 68 00 17 00
> 
> 00 00 80 59 4d 00 00 91 7b 00 51 1b 68 00 06 8a 7e 00 cd 3c 55 00 d5 fb b4
> ff c4 3b 66 00 06 00
> 
> 00 00 ec b1 32 00 a2 08 66 00 14 e9 2a 00 af 4b 56 00 02 2f 07 00 b4 41 f6
> ff a1 a1 1c 00 0f 39
> 
> 0d 00 7d c4 3b 00 91 31 00 00 68 58 fc ff 27 f3 ff ff e4 48 91 ff 75 ca 0e
> 00 3b 50 5e 00 a1 aa
> 
> ff ff 32 fe 66 00 28 bd b5 62 0b 31 68 00 07 00 00 00 80 59 4d 00 00 90 7b
> 00 51 1b 60 00 06 8a
> 
> 7e 00 cd 3c 55 00 e9 fb b4 ff c4 3b 1b 00 fd ff 00 00 ca fb 02 00 04 0a 1b
> 00 d3 73 33 00 ad 74
> 
> 71 00 01 79 08 00 ac 04 2e 00 a1 5e 06 00 05 64 0d 00 45 c4 3b 00 bc df ff
> ff 5a 61 74 00 27 c0
> 
> ff ff 7f 27 58 00 77 90 28 00 53 f6 32 00 7c a3 ff ff 10 10 1b 00 88 4b b5
> 62 0b 31 68 00 15 00
> 
> 00 00 80 59 4d 00 00 90 7b 00 51 1b 60 00 06 8a 7e 00 cd 3c 55 00 e7 fb b4
> ff c4 3b 5f 00 f0 ff
> 
> 00 00 9a e3 03 00 51 06 5f 00 ad bd 3d 00 0f b8 df ff 07 f8 04 00 91 5c 7e
> 00 a1 03 09 00 4a 19
> 
> 0d 00 7c c4 3b 00 3d 55 00 00 e3 4e 49 00 26 b8 ff ff 62 b9 0f 00 94 48 23
> 00 70 fd 28 00 9d a1
> 
> ff ff 27 18 5f 00 0c b6 b5 62 0b 30 28 00 19 00 00 00 ee 05 00 00 9f 60 59
> 00 b3 10 63 00 00 48
> 
> fd ff f7 0c a1 ff 64 8a b8 ff b0 01 ce ff 80 ec 45 00 e5 00 1f 00 ac f0 b5
> 62 0b 30 28 00 13 00
> 
> 00 00 ee 05 00 00 32 2a 53 00 f9 09 63 00 00 5c fd ff f1 0d a1 ff 4b ac 14
> 00 7d 23 f0 ff 37 ec
> 
> 
.....

Each individual message format is:
1. head: b5 62; 
2. the message class/id, e.g. 0b 01, 0b 30, 0b 31;
3. 2 bytes content length;
4. message content;
5. 2 bytes checksum.

There is no message head in offline data file from u-blox (e.g,
http://alp.u-blox.com/current_1d.alp),
this prevents us from extracting (and/or calculate) AID data then load into
u-blox GPS receiver.
As of HUI/ALM/EPH, ANTARIS_Protocol_Specification(GPS.G3-X-03002).chm says:
See ICD-GPS-200 for a full description of the contents of...
Sigh, If freerunner has flash memory, the offline data can be directly
submitted to u-blox GPS receiver. 



Helge Hafting wrote:
> 
> Cédric Berger wrote:
>> On Wed, Feb 18, 2009 at 17:49, Al Johnson <openmoko at mazikeen.demon.co.uk>
>> wrote:
>>> I may be misunderstanding the suggestion, but I don't think it had
>>> anything to
>>> do with data from ublox. The suggestion was to use data sent by other
>>> freerunner users instead of the data supplied by ublox.
>> 
>> As I understood the suggestion was in reply to :
>> 
>>>> It is not a problem that user account is required when download u-blox
>>>> online
>>>> aiding data.
>>> It is a problem since u-blox might go out of business and you might
>>> not want to tell them where you are all time. Their server also might
>>> be down. There are plenty of reasons to remove dependency to any
>>> single party.
>> 
>> The problem is that data from u-blox is a proprietary format, and as
>> far as I know, we do not know yet how to create the same data that can
>> be pushed to the GPS chip.
> 
> As far as I know - we do know the format. The SHR distribution
> already saves such data before turning the gps off, and restores it when 
> you turn it on so you get the first fix quicker.
> 
> Not all the data is used at the moment, because the process sometimes 
> fail yelding long startup times. But that should only be a debugging 
> problem.
> 
> It is already possible to set up a free server for almanac data, as 
> saving and loading almanac data works well and speed up TTFF some.
> 
> Helge Hafting
> 
> _______________________________________________
> Openmoko community mailing list
> community at lists.openmoko.org
> http://lists.openmoko.org/mailman/listinfo/community
> 
> 

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