Hammerhead/Protocol

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(removed obsolete info. Sphyrna project decoded hammerhead better.)
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Hammerhead is the GPS receiver chip used in the Neo 1973. The only way currently to use it is via a closed-source binary program. This page describes efforts to write an open source driver. (Mostly abandoned since the release of the Neo FreeRunner which uses a different chipset)
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== Repository ==
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We have set up a SCM repository for experimental code and documentation at http://projects.linuxtogo.org/projects/sphyrna.
 
We have set up a SCM repository for experimental code and documentation at http://projects.linuxtogo.org/projects/sphyrna.
  
Christian did some stracing on TomTom device, and result is great logs at http://www.maintech.de/download/hammerhead-strace.log . 'pH5' on IRC has put up some traces at http://linuxtogo.org/~ph5/tmp/gllin (a cold start, a hot start and a somewhat longer trace). He even has a software that can init and send command to phase-1 openmoko device in http://linuxtogo.org/~ph5/tmp/hhtest.c . (Please use strace -s9999 -x to produce traces).
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[[User:mmontour]] has created a quick and dirty gtk program called 'satscan' which performs the first steps of a cold-start acquisition. It scans through the satellite numbers 8 at a time in several different frequency bands, and displays a symbol on the screen indicating the strength of each signal. The program (which includes portions of 'hhtest.c') is available here: [http://members.shaw.ca/mmontour/satscan/]. Description/screenshots are 
  
A file giving doppler information on the above longtrace NMEA is on [http://www.mauve.plus.com/gps].
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[http://openmoko.togaware.com/survivor/SatScan.html]
  
[[User:mmontour]] has created a quick and dirty gtk program called 'satscan' which performs the first steps of a cold-start acquisition. It scans through the satellite numbers 8 at a time in several different frequency bands, and displays a symbol on the screen indicating the strength of each signal. The program (which includes portions of 'hhtest.c') is available here: [http://members.shaw.ca/mmontour/satscan/satscan_1.0-r0_armv4t.ipk].  
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== Background resources ==
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Christian did some stracing on TomTom device, and result is great logs at http://www.maintech.de/download/hammerhead-strace.log . 'pH5' on IRC has put up some traces at http://linuxtogo.org/~ph5/tmp/gllin (a cold start, a hot start and a somewhat longer trace). He even has a software that can init and send command to phase-1 openmoko device in http://linuxtogo.org/~ph5/tmp/hhtest.c . (Please use strace -s9999 -x to produce traces)http://folks.o-hand.com/andrew/strace-schwartz-oabi is a log of all library calls (i.e. a superset of system calls) made by gllin during a hot start and acquiring the time (but no fix), except acos() because printing all acos() calls would fill gigabytes per second.
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A file giving doppler information on the above longtrace NMEA is on [http://www.mauve.plus.com/gps].
  
 
[http://en.wikipedia.org/wiki/GPS_signals GPS signals at wikipedia] seems to be required reading for very basics, along with  [http://www.colorado.edu/geography/gcraft/notes/gps/gps.html this page from University of Colorado] for more in depth stuff.
 
[http://en.wikipedia.org/wiki/GPS_signals GPS signals at wikipedia] seems to be required reading for very basics, along with  [http://www.colorado.edu/geography/gcraft/notes/gps/gps.html this page from University of Colorado] for more in depth stuff.

Latest revision as of 13:39, 31 August 2008

Hammerhead is the GPS receiver chip used in the Neo 1973. The only way currently to use it is via a closed-source binary program. This page describes efforts to write an open source driver. (Mostly abandoned since the release of the Neo FreeRunner which uses a different chipset)

[edit] Repository

We have set up a SCM repository for experimental code and documentation at http://projects.linuxtogo.org/projects/sphyrna.

User:mmontour has created a quick and dirty gtk program called 'satscan' which performs the first steps of a cold-start acquisition. It scans through the satellite numbers 8 at a time in several different frequency bands, and displays a symbol on the screen indicating the strength of each signal. The program (which includes portions of 'hhtest.c') is available here: [1]. Description/screenshots are

[2]

[edit] Background resources

Christian did some stracing on TomTom device, and result is great logs at http://www.maintech.de/download/hammerhead-strace.log . 'pH5' on IRC has put up some traces at http://linuxtogo.org/~ph5/tmp/gllin (a cold start, a hot start and a somewhat longer trace). He even has a software that can init and send command to phase-1 openmoko device in http://linuxtogo.org/~ph5/tmp/hhtest.c . (Please use strace -s9999 -x to produce traces). http://folks.o-hand.com/andrew/strace-schwartz-oabi is a log of all library calls (i.e. a superset of system calls) made by gllin during a hot start and acquiring the time (but no fix), except acos() because printing all acos() calls would fill gigabytes per second.

A file giving doppler information on the above longtrace NMEA is on [3].

GPS signals at wikipedia seems to be required reading for very basics, along with this page from University of Colorado for more in depth stuff.

http://home.earthlink.net/~cwkelley/ has sources for open-source GPS receiver, and http://home.earthlink.net/~cwkelley/documentation.htm is its documentation.

https://okeefesrv.geomatics.ucalgary.ca/essentials/index.html provides a library of useful GPS-related algorithms under a 3-clause BSD license.

GP2021 is "dumb" GPS receiver, similar to hammerhead. (But I think it communicates over ISA bus, not over serial). However, its data sheets are freely available. Well, hammerhead marketing tells us that their GPS chip is something special, http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=3053 . It seems to differ from "dumb" receivers by doing code phase search in hardware, directly.

There is an interesting paper on increasing accuracy of commercial GPSs that may be applicable. [4]. Other interesting papers. [5] [6]

[edit] Packet format & comm protocol

See sphyrna project for up-to-date decoding info.

Personal tools

We have set up a SCM repository for experimental code and documentation at http://projects.linuxtogo.org/projects/sphyrna.

Christian did some stracing on TomTom device, and result is great logs at http://www.maintech.de/download/hammerhead-strace.log . 'pH5' on IRC has put up some traces at http://linuxtogo.org/~ph5/tmp/gllin (a cold start, a hot start and a somewhat longer trace). He even has a software that can init and send command to phase-1 openmoko device in http://linuxtogo.org/~ph5/tmp/hhtest.c . (Please use strace -s9999 -x to produce traces).

A file giving doppler information on the above longtrace NMEA is on [1].

User:mmontour has created a quick and dirty gtk program called 'satscan' which performs the first steps of a cold-start acquisition. It scans through the satellite numbers 8 at a time in several different frequency bands, and displays a symbol on the screen indicating the strength of each signal. The program (which includes portions of 'hhtest.c') is available here: [2].

GPS signals at wikipedia seems to be required reading for very basics, along with this page from University of Colorado for more in depth stuff.

http://home.earthlink.net/~cwkelley/ has sources for open-source GPS receiver, and http://home.earthlink.net/~cwkelley/documentation.htm is its documentation.

https://okeefesrv.geomatics.ucalgary.ca/essentials/index.html provides a library of useful GPS-related algorithms under a 3-clause BSD license.

GP2021 is "dumb" GPS receiver, similar to hammerhead. (But I think it communicates over ISA bus, not over serial). However, its data sheets are freely available. Well, hammerhead marketing tells us that their GPS chip is something special, http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=3053 . It seems to differ from "dumb" receivers by doing code phase search in hardware, directly.

There is an interesting paper on increasing accuracy of commercial GPSs that may be applicable. [3]. Other interesting papers. [4] [5]

Packet format & comm protocol

See sphyrna project for up-to-date decoding info.