GTM900-C + dev board

[Mychaela Falconia]

Hi Dmitry!

> I found this board on Aliexpress
> [...]
> this is a GTM900-C module + board

Our friend Songbosi shared this picture with our community back in May:

https://app.2sim.cn/gsm/huawei.jpg

It shows both GTM900-B and GTM900-C with shieldcan covers removed, and
we can clearly see that the -C version has the LoCosto chipset inside,
not Calypso.  As indicated in our name, we only support Calypso and
not LoCosto.  If you are interested in playing with LoCosto, you are
of course welcome to start your own FreeLocosto project, and we even
have a bunch of materials for that later chipset:

ftp://ftp.freecalypso.org/pub/GSM/LoCosto/

We have the schematics and PCB layout for TI's I-Sample board (their
development board for LoCosto), TCS3.2 reference fw for that board in
mostly-source form, and TI's CSST tool for feeding images to the
LoCosto boot ROM and flashing LoCosto boards - but the latter tool is
a Windows binary sans source, so you will need to reverse-eng it
yourself to crack the protocol if you wish to go that direction.

OTOH, if you would rather stick with FreeCalypso than start your own
FreeLocosto project, then you need GTM900-B, not -C.  You can buy
GTM900-B from Songbosi ($15 is very cheap in my opinion), but you will
need some breakout or development board to connect power, the SIM
socket, the two UARTs and a PWON button.  You *might* be able to buy
the GTM900-C dev board kit and then replace the module with the -B
version, but I don't know if the interface pinout is the same between
-B and -C or not.

HTH,
M~