GTA04 Block V4 / GPS data
karsten.at.openmoko at onlinehome.de
Sun May 11 08:58:36 CEST 2008
Ian Stirling schrieb:
> Andy Green wrote:
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>> 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.
That was the idea behind my question (do you can read someones mind? ;-) )
> 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.
This update frequency is not enough for "real" usage.
Imagine a bicycle ride with 20 km/h. That is 5,5 meter per second.
A update every 5 second would mean 27 Meters between measurement
point. This is not accurate enough to record a single trail ride,
for instance. To get good results in this case, one should consider
an update frequency of one or two per second.
If the MPU would write all the GPS data to a SD, one (developer of
the GPS application) could delay the analysis to the moment, the
user wants to see the route. Even just "buffering" the GPS data for
5 or 10 seconds (means: no SD access) before "calling" the cpu would
But I doubt that anyone else beside me sees this as a valuable usage
of a GTA0x, or even as an additional benefit. To me it seems as if
everybody tries to incorporate the GSM part in ANY idea to legitimate
a GTA0x as a solution.
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