Hi Mychaela,
(I changed the Subject when replying, since this topic is not specific
to Sony Ericsson K2xx.)
On 23.09.2024 04:58, Mychaela Falconia wrote:
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?
I would be interested to play with the DSP directly using osmocom-bb
code base. While working on adding CSD support for it, I had to make
only a small change to the layer1 firmware to get the channel coding
working:
https://cgit.osmocom.org/osmocom-bb/commit/?id=069b627abecad7efb4de43e3bad7ceb685d65e89
Back then I was primarily focusing on getting full-rate data calls
working and sadly had no time to test half-rate calls.
In theory, both TCH/H2.4 and TCH/H4.8 should be supported by
osmo-bts-trx; we even have TTCN-3 testcases for that. There might be
missing bits in osmo-bsc and/or osmo-msc, though.
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.
If I remember correctly, it was mentioned somewhere (or by somebody in a
conversation) that TI's DSP has a hardware accelerated module for the
V.110 stuff (RA1'/RA1/RA2 functions). I guess this could be it? In the
case of osmocom-bb, we're doing all the bit manipulations in software on
the host side. This is not a big deal for a modern x86_64 machine, but
could likely be offloaded to the DSP in the phone's normal firmware.
--
Best regards,
Vadim.
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