GTA04 Block V4 / GPS data

Ian Stirling OpenMoko at
Tue May 6 21:53:15 CEST 2008

Andy Green wrote:
> Hash: SHA1
> Somebody in the thread at some point said:
> | I don't know how much current the GPS chip consumes and if it
> | is possible at all, regarding battery capacity, to run this
> | beast continuously, but it would be an outstanding feature if
> | one could record the GPS data for a whole day.
> The MPU won't help directly for this since we didn't plan to put GPS
> through it.  (But actually, if we don't use the battery backup feature
> of the GPS again, it is quite interesting if the ephemeris store and
> restore lived in there: it could power up GPS, restore ephemeris and
> wake CPU only when there was a new result)
> Currently it costs around ~30mA at 3.3V to run the GPS device actively and
> another 14mA at 3V to run the active antenna, it comes to 141mW.  Then as
> you note you have to have the CPU up at 400MHz to process the data,
> which is "expensive", hundreds of mW.
400MHz is certainly overkill.
On GTA01 - with the modem off - but with the LCD still updating (but 
backlight off) with CPU set to 100MHz, I've gotten it to 400mW - without 
doing much.

This is 12 hours.

The CPU in GTA04 claims - as I understand it - I haven't gotten a full 
datasheet yet - to have powersaving modes.
If this is at least similar to GTA01, 24h should be easily doable.

The solution I suspect I'd end up if I was designing the phone would be 
a significantly more capable MPU, with the ability to do more 'stuff' - 
with the CPU off, including act as an SD expander, and write debug state 
or GPS to SD, or even stream data from there to a mp3 decoder, but 
that's me.

If the GPS can be set to update every 5 or 30s, then 'simply' optimising 
the suspend/resume path to happen quickly enough may work.

More information about the hardware mailing list