GTM900 support update

[Mychaela Falconia]

Hello again everyone,

The recent developments in FC Magnetite including GTM900 target support
have been synced into FC Selenite, thus you can now play with both fw
versions on these GTM900 modems.  The only caveat is that the gcc-built
version of Selenite needs to be configured with GPRS=0, otherwise the
GPRS-enabled, gcc-built fw config fails to fit into the small (256 KiB)
IRAM in the Calypso Lite chip.  However, when building with the
original TMS470 compiler (either Magnetite or Selenite), the standard
GPRS-enabled fw config fits just fine in the available memories.

The most likely reason for the unexpected IRAM shortage is that I
compile IRAM code pieces in ARM mode, whereas TI's original TMS470
setup compiles almost everything in Thumb, including IRAM code.  My
approach of compiling XIP code in Thumb, IRAM code in ARM works fine
when building full-featured fw for targets with full Calypso chips
(FCDEV3B and OM GTA02 modem) or voice+SMS-only fw for Mot C1xx, but
the combination of full functionality plus Calypso Lite chip (became
a possibility for the first time with the arrival of the GTM900) turns
out to not fit.  Oh well.

The GTM900 also has 2 MiB of XRAM, and our Selenite-gcc GPRS=0 fw can
be built as either flashable or RAM-loadable like on the C155 target.
Unlike the situation on Mot C1xx phones, our FC firmwares on the GTM900
use Huawei's original FFS, but there is a caveat: if you leave Huawei's
original fw in the flash and run Selenite-gcc GPRS=0 fw via fc-xram,
our fw will operate on the FFS in read/write mode (TIFFS has no option
of a "read-only mount"), and I would not trust the combination of
Huawei's fw working with an FFS that has been written to by FreeCalypso
fw.  So please make a full flash dump with fc-loadtool first, and save
it in a safe place.

If you are going to flash either Magnetite or Selenite fw on your
GTM900, you should likewise save a full flash dump first.  If you are
then going to flash back to Huawei's fw, you will need to restore the
full flash dump, not just the fw portion - this way there will be no
lasting effects from the FFS having been messed with.

Off to bed now - sorry if I missed some detail in my tired state.

M~