New FC host tools and modem fw releases

Mychaela Falconia falcon at
Thu Jun 8 22:07:56 UTC 2023

Hello FreeCalypso community,

I just put out a new release of FC host tools:

and new official stable firmware builds for FreeCalypso modems:

FC host tools noteworthy changes: the only truly interesting changes
from r18 to r19 involve rvinterf logging.  If you are interested in
tracing primitive exchanges between protocol stack components, as
described in the Frame Users Guide document from TI, the new version
of rvinterf has its max Rx packet length limit raised to match what
the firmware can send, and the new session log format is more sensible
and useful.  Another logging-related change that should be readily
noticeable is that non-printable bytes mixed into places where ASCII
strings are expected are now printed in C-style backslash escape form,
rather than 'cat -v' form.

Modem firmware changes since the last official build dated 20210811:

1) New AT%MSCAP and AT%SPVER commands, documented in the new
Speech-codec-selection article in freecalypso-docs, allow you to
modify the speech version list sent to the network in the Bearer
capability IE for both MO and MT voice calls, thereby telling your
local GSM operator's network "alternative truths" about which codecs
your MS supports.  Using this feature, you can determine experimentally
how your network handles GSM MS that don't support AMR (FreeCalypso
does support AMR, but with the new feature you can lie to the network
and say that it doesn't), and at least in my part of the world such
Bearer cap IE manipulation is the only way to coax the network into
giving you TCH/FS or TCH/EFS rather than TCH/AHS.

2) Once you do get a non-AMR speech TCH out of your network (whether
by doing the above manipulation or by operating your own GSM network
that always runs with non-AMR codecs), the new firmware includes a
resurrected form of our TCH tap feature, implemented properly this
time around.  Using the new firmware together with fc-host-tools-r18
or later (the just-released fc-host-tools-r19 version is obviously
preferred, but r18 will work too for this purpose), you can capture a
complete recording of TCH/FS, TCH/HS or TCH/EFS DL, and then analyze
that TCH DL recording (including correct decoding all the way to
playable audio) with tools contained in the recently developed and
released Themyscira GSM codec libraries & utilities package.  You can
likewise prepare your own FR and EFR speech recordings and play them
into TCH UL with the same tools.

Some time later this month (2023-06) I plan on going back to Tijuana
(Mexico) with an extra Pirelli DP-L10 phone (on which I can also do
all of the above tricks, and which is easier to carry in "field"
conditions than a full devboard setup) and a freshly purchased, but
still GSM-supporting Telcel SIM, and doing the experiments to see how
that Mexican GSM network handles GSM MS that declare themselves as
non-AMR-capable.  I already know how the not-yet-shutdown network of
T-Mobile USA handles such (always prefers AMR, but goes down to EFR if
the MS supports EFR but not AMR, or down to FR1 if the MS supports
neither AMR nor EFR - but never does HR1), but Telcel MX remains to be

I would also be very interested in field reports from other parts of
the world: I know we have community members in Western EU and in
Russia/Kazakhstan who have FCDEV3B hardware and the necessary GSM
tinkerer skill level - how does your country's GSM network act in
terms of speech codec selection?  Does your network always go for AMR
given an AMR-capable MS, or are there any commercial GSM networks
anywhere in the world that are natively non-AMR?  If your country's
network is AMR-native or AMR-preferring, how does it act when the MS
declares no AMR support?  Does it go down to EFR?  Or to HR1?  FR1?
Are there any commercial GSM networks anywhere in the world that use
HR1 codec?

Finally, for people who are building new GSM networks (to serve as
replacements for those being wrongfully shut down) using Osmocom CNI
software, in just under two weeks I will be giving a talk on correct
handling of non-AMR (i.e., FR/HR/EFR) speech codecs in Osmocom-based

Hasta la Victoria, Siempre,
Mychaela aka The Mother

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