Sony Ericsson K205 joins the party!

[Mychaela Falconia]

Hi Vadim,

> I am reaching out here to share some of my findings regarding the 
> K2xx-series of Sony Ericsson phones.  TL;DR, Sony Ericsson K205 is 
> another Calypso based phone, among with the known K200/K220 pair.

Thank you for this update.  It is nice to know that one more phone
exists with our beloved Calypso and with fairly interesting original
fw.  For those who don't know, the original fw on SE K2xx family has
these interesting qualities:

1) It remains reasonably close to TI TCS211 baseline, which is a rarity
among mass-produced Calypso phones: most of the latter exhibit fw
architectures that have been revamped beyond recognition.

2) It can be put into a mode in which it presents an AT command
interface on its lone UART, and that AT command interface includes CSD
capability.  And just like real TCS211, this CSD support includes
transparent mode, which appears to be a rarity among non-TI
implementations.

Speaking of CSD, the one readily apparent limitation of CSD support in
TI's full solution is the lack of support for CSD on TCH/H.  More
precisely, I see various definitions for CSD on TCH/H, it looks like
certain parts are present, but the end-to-end solution clearly lacks
working support for these modes.  I haven't studied it enough to tell
if the limitation is in the DSP ROM (unalterable), in TI's official
DSP patches (amenable to modification in theory, but extremely
difficult) or in ARM firmware which could be easily extended.  Has
Vadim or anyone else looked into it?

For Vadim or anyone else who may wish to look into it, look in L1 code
and particularly in L1-DSP interface for something called IDS - that
specific C preprocessor symbol.  (It presumably stands for Integrated
Data Services, IIRC.)  It looks like the DSP has some dedicated words
or buffers in its shared memory interface that are devoted to this IDS
feature, but I haven't taken the time to study exactly what they
correspond to in the air interface layer stacking.  In other words, if
one takes the air interface definition for CS data services starting
with R-interface characters at the top and burst modulation at the
bottom, exactly at which level did TI draw the interface between the
DSP and ARM firmware?  It seems to be a little above the GSM 05.03
channel coding layer, but exactly how far above?  And what do they
do differently, if anything, between transparent and RLP services?
(Of course the upper layers are different, but I am wondering about
the DSP interface and that mystery IDS mechanism, whatever it actually
does.)

If no one beats me to it, I definitely plan on looking into this area
later - but it may be quite significantly far down the road, as I have
so many higher priorities...

> Please find a patch for freecalypso-tools attached.

Thanks, I'll apply it shortly, and I may also do some additional
documentation polish while at it.

M~