[maemo-users] GPS receiver problem after N800 flash

From: Marius Gedminas marius at pov.lt
Date: Sun Apr 1 23:32:49 EEST 2007
On Sun, Apr 01, 2007 at 10:19:00PM +0200, Benjamí Villoslada wrote:
> El Diumenge 01 Abril 2007 19:45, Marius Gedminas va escriure:
> >   * I have not registered my GPS anywhere in the control panel.  I've
> >     heard that N800 comes with gpsd that allows multiple applications to
> >     use the GPS at the same time.  Perhaps Maemo Mapper instead of using
> >     gpsd tries to access the GPS directly and they conflict?
> I've registered the GPS device in order to change something related to the 
> problem after flashing.  Now is unregistered.
> (all work fine with the previous firmware)
> >   * Does your device send proper NMEA sequences?  There should be a way
> >     to test it with rfcomm bind rfcomm0 XX:XX:XX:XX:XX followed by
> >     cat /dev/rfcomm0.  If you get binary gunk instead, then your GPS is
> >     switched to some other protocol (e.g. SiRF) and Maemo Mapper does
> >     not understand it.  It is possible that these unexpected messages
> >     may trigger a bug in Maemo Mapper's parser causing it to loop
> >     forever.
> Nokia-N800-10:~# rfcomm bind rfcomm0 00:0B:0D:84:D0:15
> Nokia-N800-10:~# cat /dev/rfcomm0
> $GPGGA,200757.000,3938.6060,N,00300.6637,E,1,08,1.0,126.6,M,51.1,M,,0000*52

Looks like NMEA to me.

> > The best way to figure out what is happening would be to build
> > maemo-mapper with debug symbols and attach gdb to it when it starts
> > looping.
> Any maemo gdb HOWTO? :)

Get root (or the red pill), then install the gdb package.

'pidof maemo-mapper' in a terminal will show you the process IDs.  I see
two; are those threads or processes?  IIRC 2.4 kernel with linuxthreads
had a PID per thread, while 2.6 with NPTL has all threads share the same
PID.  I seem to remember in one discussion here a mention that Maemo
does not have NPTL.  I guess these are threads then.

Anyway, gdb /usr/bin/maemo-mapper 1234 will attach itself to the running
process (replace 1234 with the real PID), and then 'bt' will show the
stack trace.  At least that's how you do it on a normal system.  I don't
really know if Maemo has any specifics.

Marius Gedminas
Programs that write programs are the happiest programs in the world.
        -- Andrew Hume
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