GTM900 support update

[Mychaela Falconia]

Serg wrote:

> Thank you Mychaela, this pretty nice platform as an alternative to C1xx
> phones. While it is not as robust as FCDEV3B, it makes it a usable platform
> for some applications development.

For anyone interested in playing with FreeCalypso just for fun and
recreating as closely as possible the environment which TI's own sw/fw
developers had in their offices or cubicles Back In The Day, this new
GTM900 find is definitely better than Mot C1xx, and only one step below
my FCDEV3B, which is in turn one step below TI's own D-Sample board
for which we have no schematics (thus no complete understanding), no
PCB layout files (thus no ability to make more of those boards) and no
tpudrv10.c module.  The main advantages of GTM900 over C1xx are (1) it
is a modem rather than a phone, thus runs modem fw more natively
without VPM hacks, (2) both UARTs are brought out, allowing the full
TI/FC dual UART architecture to be fully enjoyed with GPRS, CSD and
the GSM 07.10 MUX, and (3) the GTM900 is unbrickable unlike C1xx.

OTOH, for commercial applications needing a GSM/GPRS modem module, the
two biggest differences between the already existing and available
GTM900 and what I seek to produce if anyone ever funds it are (1) my
module would be at least triband and preferably quadband, and (2) my
module would have Calypso MCSI brought out for a digital voice
interface as recently proven on the FCDEV3B, a feature not present in
any of the historical commercial packaged modem modules with the
Calypso chipset.

Also if anyone ever does fund the development of a new FreeCalypso
commercial modem module, I would like to make it more modular, excuse
the pun: instead of making a module with connectorized interfaces like
GTM900 from the get-go, the first version (the most basic core) should
be an SMT module more like BenQ M32, and once we have this basic core,
repackaging it into a form factor more like GTM900 for those who
desire such would be trivial.  The rationale is that an M32-like
module can be trivially transformed into a GTM900-like one, but not
the other way around.

> I have done a quick search for a dev board schematics and here is an easy
> find.

On a short timescale schematics like the one you found aren't of any
help, as it is just schematics, not a PCB design which one could send
to a fab.  On a longer timescale where I will be doing my own PCB
design for the breakout/interface board, those schematics aren't of
much interest either: they don't tell me anything I didn't already
know, and my version will be different in several ways.

> I also found this document which describes some other variants of GTM900.
> Looks like 850/1900 band is supported in GTM900-P

Now this one looks interesting!  The PCB inside GTM900-B is designed
so it can be populated in one of two ways, for either dual-eu or
dual-us bands, so perhaps GTM900-P is the latter version indeed.

> I'm going to get one and decap.

I searched for places to buy a GTM900-P, and found only two sellers on
Alibaba (not Aliexpress), one listing the price as $50-90 and the other
as $50-99 per piece.  Assuming that single unit quantities would be on
the upper end of this range, it is certainly more expensive than what
our friend Songbosi is selling the EU-band version for, but looking at
it the other way, it would still be cheaper than the cost of having
Technotronix and Falconia Partners LLC modify and recalibrate these
modules in California at USA fair labor rates.

M~