The goal of the gcc-built Calypso GSM firmware project contained in the gsm-fw
directory of this source tree is to replace the Windows-built firmwares which
have been produced in other subprojects under the FreeCalypso umbrella - see
leo2moko and tcs211-c139.  Our leo2moko project has produced a production
quality modem fw image for the Openmoko GTA02, while a C139 reflashed with
tcs211-c139 is the first dumbphone in history that can still function as an
untethered phone after having had its fw replaced with an indie one that bears
no relation to the manufacturer's original - but those TCS211-based
Windows-built projects have severe limitations.  Much of the firmware code base
in those versions is in the form of unmodifiable binary object libraries, and
the Windows-based configuration and build system is incompatible with the
long-term needs of FreeCalypso development.

The present FreeCalypso GSM fw project seeks to rectify the situation by
replacing the blob-laden, Windows-built firmware with a version that is built
from full source (no binary blobs) with gcc, with an entirely different
configuration mechanism that actually suits our needs.  Because one of the key
goals of this project is to build the firmware from *full source*, the binary
object versions of L1 (GSM Layer 1) and G23M (layers 2&3 of the protocol stack)
featured in our reference TCS211 fw could not be reused.  Instead this project
uses versions of L1 and G23M (and some other pieces) that have been lifted from
the firmware for TI's other chipset (LoCosto) and backported to Calypso.

The current state of the project is that we have made remarkable progress, but
are unfortunately nowhere near the goal of actually being able to replace TCS211
for practical use.  Specifically:

* Only the bare minimal modem functionality for the voice+SMS subset has been
  integrated so far.  "Modem" means our fw can only be controlled via AT
  commands; no UI code (as in LCD+keypad) has been integrated at all.  But it
  is not a true modem either as none of the data functions have been integrated
  yet: no CSD, no fax, no GPRS.  Thus it is an AT-command-controlled voice+SMS
  pseudo-modem.

* The firmware can be built for the following targets:

  Mot C11x/12x
  Mot C139/140
  Mot C155/156
  Openmoko GTA01/02
  Pirelli DP-L10

  All configurations are built from the same source tree.  The firmware
  functions identically on all supported targets.  Because there is no UI code
  integrated yet, the LCD stays dark and the buttons do nothing on those target
  devices that have such hardware.

* Most of our supported target devices have only one practically accessible
  serial port (UART).  Our firmware presents TI's RVTMUX interface on this
  UART; the operator is expected to interface to it by running our rvinterf
  tools on the host PC/laptop.  One of the utilities in the rvinterf suite is
  fc-shell; this tool is used to send AT commands to the running firmware,
  which is the only way to control its operation.

* With a valid SIM card inserted and a valid IMEISV configured, a GSM device
  running our firmware can successfully connect to live commercial GSM networks
  and send and receive SMS.

* Voice calls are broken: using appropriate AT commands, one can dial outgoing
  calls and answer incoming ones, and they connect as they should.  However,
  the voice audio path is broken: nothing but noise is heard in the earpiece
  speaker.  We reason that the problem must be somewhere in L1, which has been
  backported from LoCosto to Calypso in a rather Frankensteinian manner.

* Deep sleep is broken and needs to be disabled with AT%SLEEP=2; the breakage
  is likewise assumed to be somewhere in L1.

The two current points of breakage in L1 (broken deep sleep and broken voice
calls) are deemed to be show-stoppers, i.e., we are not going to progress this
work in any other direction until these two are fixed.  And we currently see
only two possible ways to fix these L1 issues:

Option 1: find and obtain another copy of TCS211 that has its L1 component in
source form, or a separate L1-by-itself source that would be compatible with
Calypso DSP ROM 3606 and with the TCS211 fw architecture.

Option 2: painstakingly reconstruct a TCS211-fitting version of L1 from the
disassembly of the available binary objects, by taking LoCosto L1 sources and
massaging them until they compile into object code that matches our TCS211
reference.

Option 1 involves more prayer than actionable work, while Option 2 is currently
being worked on in another subproject of FreeCalypso - see tcs211-l1-reconst.