[Gta04-owner] gpsd software

[NeilBrown]

On Sun, 4 Dec 2011 21:02:53 +0100 "Dr. H. Nikolaus Schaller"
<hns at goldelico.com> wrote:

> 
> Am 04.12.2011 um 01:28 schrieb Neil Jerram:
> 
> > I just wanted to point out that the latest gpsd (3.x) has a nice feature
> > that I believe allows providing GPS on demand with no need for an
> > "enable GPS" switch or something like "fsoraw -r GPS ...".
> > 
> > That is, it calls a hook script (/etc/gpsd/device-hook $DEVICE ACTIVATE)
> > when the first client connects on the gpsd port, and similarly
> > ((/etc/gpsd/device-hook $DEVICE DEACTIVATE) when the last client
> > disconnects from that port.
> > 
> > For GTA04, I think that means we can put the commands to enable and
> > disable GPS power into that script, and then just run gpsd all the time.
> 
> That is really a nice feature!
> 
> One thing we have to consider - the reset impulse for the
> GPS module is a toggle switch. Each impulse toggles between
> power on/standby. And the only method I know to detect
> in which state it is is to check if there are NMEA records
> on the serial line.
> 
> The GTA04 tester sends one impulse and waits up to 5 seconds
> if there arrive NMEA records. If not, it sends another impulse.
> 
> I don't know if that can be done by this type scripts and gpsd.
> 

This 'toggle' nature of the standby line makes it hard to write an 'rfkill'
driver to powerup/powerdown the gps :-(

It appears that you can send a SiRF command over the serial line to force a
power-off (though I haven't tested yet).  If that works, I plan to get the
'rfkill' to pulse the line at power-on and arrange some udev script to send
the power-off command when the rfkill switches to 'off'.

Then the gpsd script would just 
   rfkill block gps
or
   rfkill unblock gps

which is nice and generic.

NeilBrown
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