Post- GTA02

joerg joerg.twinklephone at gmx.de
Fri Mar 21 21:57:55 CET 2008


Am Fr  21. März 2008 schrieben Sie, Andy Green:
> - gpg control packet
> Somebody in the thread at some point said:
> > Am Fr  21. März 2008 schrieb Andy Green:
> >>> Yep, i see. But we have to drive the LCM anyway during call, no?
> >> I don't know why we do that when it is just illuminating your earlobes.
> >
> > There has to be a way (=button, =LCM) to end the call at least ;-)
> > Sure it's not nice to have CPU running full power for some task that can 
> > be 
> > done in GSM chipset (though i'm not sure this is a common feature for 
> > these 
> > chips. Maybe we really need a specialized chip for this), but switching 
> > off 
> > display is sth that can be done only while you really have the phone 
> > pressed 
> > to your ear - there are all kinds of user interaction (e.g. Hold,
> > Mute/Volume, DTMF) and usefull info (e.g. duration, BattState) during
> > established call, that need a working LCM. We have no keyboard! Just TS.
> > You're not suggesting an interface-free phone you have to shake or sth to 
> > end the call?
> 
> I wonder if it can track in which orientation you hold the phone while
> you are speaking, and wake the CPU and display when this changes beyond
> some threshold.
> 
> One way or another moving the phone from your ear to where you can see
> the display to change states (or even see the battery state or call
> duration or buttons for DTMF or volume) is a "gesture" we can detect and
> react to by waking the CPU.

Yep, waking isn't the problem, like you say, by detecting "gesture".
The point is when to switch off the display. There's no way to relyably 
detect "on ear" by using G-meters. 
Anyway this thread is about things we need in GTA03+. Obviously a proximity 
detector (like in some nokia phone) to detect "on ear" is very useful. IR 
refektion, capacitive, or ultrasonic type comes to mind. Probably IR is best, 
to distinguish "on ear" from approaching hand when pressing a key.
On nokia (also IR, forgot the model) this was used to switch off freehand, not 
to blow your ear, IIRC.

> 
> > However, to throttle down the CPU while call sure is a good thing, that's
> > worth looking for different ways to cancel echo.
> 
> Well we can think about it some more, but the biggest win can come when
> we suspend the CPU, it is the natural first goal I think.  And because
> the GSM stuff is so autonomous already and interaction during a call is
> relatively rare, it seems possible.

Sure it's a must, that is if we know to tell for sure when it's "on ear". That 
for i even thought of using a dedicated echo-cancellation chip, if we really 
need echo-c while "on ear". 
When in handsfree speaker mode (the real echo prone situation), we mustn't 
switch off display anyway, so CPU has to be up at least to video mode, as 
long as we talk of 6400 CPU and using it for driving LCM. So in this 
operation mode, in relation to audio-amp + backlight + CPU video mode needed, 
it's no big difference to clock the CPU with e.g. 300MHz to do the echo-c. 

A simple echo-suppression by inverse leveling of speaker and mic (adaptive 
half duplex, used by vast majority of cheap handsfree phones) is easily done 
with 1MHz CPU clock (or MPU, if it may access wolfson mixer).

cheers
jOERG




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