[Community] GTA04A5 ready to be pre-ordered

NeilBrown neilb at suse.de
Thu Nov 7 00:02:08 CET 2013

On Wed, 23 Jan 2013 12:20:01 +0100 "Dr. H. Nikolaus Schaller"
<hns at goldelico.com> wrote:

Seeing you are considering trying again for the GTA04a5, I thought I might
re-visit these issues:

> Am 22.01.2013 um 12:29 schrieb NeilBrown:
> > On Tue, 22 Jan 2013 10:02:38 +0100 "Dr. H. Nikolaus Schaller"
> > <hns at goldelico.com> wrote:
> > 
> > 
> >> Preliminary (there may still come minor changes coming from PCB
> >> Layout tuning and from first production feedback) schematics can be found here:
> >> 
> >> 	<http://projects.goldelico.com/p/gta04-main/downloads/48/>
> > 
> > Thanks!
> > 
> > One thing that has always bothered me a little bit is that the FM transceiver
> > is wired for digital IO rather than analog.  That means that the CPU needs to
> > be active to copy sound around in order to listen to the radio.  If the
> > LOUT/ROUT pins were connected to the line-in pins on the audio chip you
> > should be able to listen to the radio with the CPU off.
> Yes, that should be possible.
> > It would mean that you couldn't get the same fidelity if you wanted a digital
> > copy of the broadcast, but I wonder if that really matters.
> > 
> > What is the expected use-case of the FM radio?  If it is just for listening
> > to, the current config doesn't seem to be optimal.
> Well, the TX direction is more interesting since it can play sound (incl. navigation
> information) to a car radio. By using text2speech. And mix with sound.
> Connecting to the Audio in is a problem since we have already connected them
> to the headset jack. So that it is possible to record sound fed into the headset
> jack. I.e. portable audio recorder...

Is the "portable audio recorder" use case more valuable than the "FM radio
without excessive power usage" use case?  I would be happy to sacrifice the
stereo-aux-in if it meant I could listen to the radio for longer.

For the price of another analogue switch like the one you use to isolate the
headset outputs (U703) you could support both FM and AUX inputs.  Maybe that
price is too high??

> And the FM-analog out are multiplexed with the digital interface on the Si4721.
> So we would need some analog/digital switching circuits where we don't have
> space for :(

I wouldn't suggest enabling both the analogue and digital interfaces.  Just
the analogue.  Digital might be nice but isn't really necessary.

> > Related: have you thought about connecting the bluetooth PCM interface
> > directly to the TPS chip in the same way that the Modem's PCM interface is
> > connected?
> > 
> > That should allow the use of a bluetooth headset on a phone call without any
> > CPU intervention.
> Yes, that could work to add these 2 wires (at least in the schematics - I don't
> know if we can squeeze them into the PCB wire hairball). And I have checked
> that these two pins at the TPS65950 come up in GPIO (input) mode, i.e.
> don't interfere.
> One issue could be that there is no BSP clock for that interface on the TPS side.
> I.e. it is shared with some other interface and I am not sure how to operate it correctly.
> So we might have to wire up something else to really make it work.

The clock for the bluetooth interface and the voice interface are shared.
So the clock from the GSM module drives the whole chain from bluetooth
through TWL4030 to GSM.

> > Just thinking out loud - looking forward to the A5 being a reality!
> So I find both proposals really good, but I hesitate to add them... may need a lot
> of work to add, and may finally not work. The problem with hardware is that
> we have to do it 100% right or risk scrapping a big set of PCBs or costly rework
> in the production line. Unfortunately there is no apt-get upgrade or git pull for
> the wires on a PCB...

:-)  I'm waiting for the day when a 3D printer can print a fully populated
multi-layer PCB (under voice command of course).

Maybe in the spirit of openness a vote might be  instructive.
  Does anyone actually want stereo aux input through the 2.5mm jack?
  Does anyone actually want to listen to the FM radio without wasting power?

(no and yes for me).

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