[Gta04-owner] Sound devices in the GTA04

[NeilBrown]

I often get confused by the myriad options that "alsamixer" present to me for
the sound card in the Freerunner and the Phoenux.

So having read through lots of docs and figured most of it out for the
Phoenux I thought I would write down what I know in the hope that 
 a/ it will be useful to others, and
 b/ if I am wrong about something, someone will tell me.
 c/ it will force me to confirm that my understanding is complete.


There are 4 sound devices in the Pheonux - each wired directly to the OMAP
SOC (each to a different McBSP port - multi-channel buffered serial port).

Three of them are very simple.
   gta04voice - the sound to and from the GSM chip
   gta04headset - sound to and from the bluetooth chip
   gta04fm - sound to/from the FM transceiver (not in 3.2 yet)

They don't have any mixer controls - they just send and receive data in a
fixed format at a fixed rate (or maybe a small selection of rates).

The other is more complex:  "gta04" is provided by the TWL4030.  It has
some functionality that is not connected in the GTA04 so we should try to
hide it from ALSA so I don't keep getting confused.

The best starting point is the diagram on page 692 of the doco for
TPS65950 aka TWL4030 referenced in table 5.1 of the GTA04 manual.
It is figure 14-6.  It displays "Option 1".  "Option 2" doesn't make sense for
the GTA04A3 due to the connections available.


There are 2 input channels, 'left' and 'right'.

'left' can be connected to:
  - on-board microphone                                 "Analog Left Main Mic"
  - headset microphone                                  "Analog Left Headset Mic"
  - AUX input line on alternate cable in headset jack   "Analog Left AUXL"

'right' can be connected to
  - AUX input line on alternate cable in headset jack   "Analog Right AUXR"

Both channels have adjustable gain:  "Analog"

(For these to be accessable "TX1" and "TX2" must be set to "Analog" - we
should try to impose that in the kernel and hide those settings).

The output side is a bit more complex.  There are 4 digital channels allowing
quadraphonic sound!  Left and Right, Front and Back.  They can be mixed in
various ways with each other and with the amplified input streams and sent to
various output devices.

The 'front' channels are labelled '1' and the 'back' channels '2', so
'Right1' is Front/Right.  To avoid confusion I'll stick with '1' and '2' as
those are the labels used in the ALSA device - just remember that '1' is the
primary (front) pair and '2' is the secondary (back) pair.

Some mixing and amplification happens digitally and then 4 digital signals
are fed into 4 DACs - DAC1 and DAC2 each with left and right channels - to
produce analogue signals.  Each of these has a fine-grained and a
course-grained digital amplifier before the DAC.  So a digital signal goes
through:

 "DACn Digital Fine" then "DACn Digital Coarse" then becomes analogue and
    goes through "DACn Analog".

Each of these are stereo and with n={1,2} so we have 4 paths.

The hardware allows these 4 paths to be fed from various sources however
the current driver doesn't support switching and the obvious defaults are
used.
The hardware allows the '1' (front) paths to be fed from either 'front' or
'back' of the appropriate side, or an L+R mix of either front or back (so 4
options).
The '2' (back) paths can be fed from the 'back' of the appropriate side
or a mix of L+R from the back (so 2 options).

The lack of driver support means that e.g. you cannot send a stereo signal to
the audio device and have the channels mixed and sent out the single speaker
of the GTA02 case.  So I'll probably have to fix that short-coming.

The 4 amplified analogue signals are optionally mixed with either the left or
right input channel (to provide a Voice Side-tone) in the main amplifier
stage.  These are controlled by the switches
   "Left1 Analog Loopback", "Right1 Analog Loopback"
   "Left2 Analog Loopback", "Right2 Analog Loopback".

There is then a 5th analogue amplifier which just takes the Voice Loopback
(sidetone) signal and amplifies it separately to the digitally provided
signals.

These 5 signals can be mixed or multiplexed into various output devices:
(The "hands free" speakers can just select one signal, the other outputs can
choose a mix of signals).

The "headset" (plugged in to 2.5mm jack) has a Left and a Right.
Each can receive a mix of 
  Voice,  DAC1,  DAC2
(where Voice is the side-tone loopback - a single channel - and DAC1 and
DAC2 are either the Left or Right as appropriate).

Then there are the speakers which is where I get confused again.
There can be 2 "HandsFree" speakers, and 1 "Ear" speaker - or maybe Earphone.

The HandsFree seem to be the 2 speakers in the GTA01 case, or just the Left
HandsFree is the single speaker in the GTA02 case.

The gta04 Schematic shows the Ear connections wired to something labelled
"CASEEAR" (Case Ear) but I cannot see where that appears on the board layout.
I would assume that this is just a future-expansion port, except that the
"sound-demo" script provided sets the volume for "Ear" but does not set the
input for "HandsFree".  so - confused.

Anyway, the HandsFree speakers can get just one signal selected from
  Voice DAC1(appropriate side) DAC2-Left DAC2-Right.

These are controlled by the "HandsfreeL Mux" and "HandsfreeR Mux" which can
be set to one of "Voice", "AudioL1", "AudioL2", "AudioR1", "AudioR2".


and the EAR speaker can get a mix of:
  Voice, DAC1-left, DAC1-right, or DAC2-left.
by muting or enabling:
 "Earpiece Mixer AudioL1", "Earpiece Mixer AudioL2"
 "Earpiece Mixer AudioR1", "Voice".


Aside from all this, any one of the 4 (mixed) digital signals can be feed to
a Pulse-Width-Modulator to drive the VibraMotor by setting "Vibra Mux" and
some other "Vibra" settings.


So that is how it works in GTA04A3.  I've heard rumours that there is a
change for the A4 so I'll say something about that...

The TWL4030 (aka TPS65950) allows digital connections directly to the GSM
Modem and the bluetooth controller.  I believe GSM is connected in GTA04A4 -
don't know about bluetooth.
This allows the TWL4030 to be configured (Option 2) to forward audio between
the mic/speakers or the bluetooth controller  and the GSM Modem.  That way
the CPU can just set up the audio channels and let the phone call progress
without being involved - it could even go to sleep to save power.

Also the FM radio *could* be wired to the TWL4030 as the "AUX In" so you
could listen to the radio without needing the CPU to copy data around.

So I'm curious as to why bluetooth and GSM aren't wired directly to the
TWL4030 in the A3, and exactly what is wired in the A4.   Nikolaus??

I'd also be happy if someone could clarify what "CASEEAR" is all about.

Oh, and "Happy new year" and all that.

NeilBrown

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