The goal of the Citrine firmware project 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 fw project (FreeCalypso Citrine) 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
what we have right now is still not a satisfactory replacement for TCS211.
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,
  make and receive voice calls, and send and receive SMS.

* In the case of voice calls, the call downlink audio is routed to the phone's
  earpiece speaker and the phone's microphone serves as the source for the
  uplink audio, i.e., even though the LCD and keypad are dead with our fw, the
  earpiece and mic continue to function as in a conventional phone.  FR, EFR
  and AMR codecs all work correctly (EFR and AMR were broken until recently),
  but our default build configuration has AMR disabled (the fw advertises to
  the GSM network that the MS only supports FR, HR and EFR codecs) to err on
  the side of safety: we are having some reliability issues with the
  L1_DYN_DSP_DWNLD feature (which is also disabled by default), and AMR is
  believed to depend on one of these dynamically downloaded DSP patches.

  There is also a highly experimental and minimally tested alternative mode
  of operation in which the traffic channel carrying FR or EFR codec bits
  (260 bits every 20 ms) is rerouted away from the internal vocoder to the
  external host, such that you can receive the downlink voice bits digitally
  instead of listening to them in the earpiece speaker, and you can substitute
  your own uplink bits instead of the microphone-fed internal vocoder output.
  See the TCH-special-feature write-up for more information.

Target-specific usage instructions
==================================

If you would like to play with our work-in-progress firmware and check it out
for yourself, see the following target-specific instructions:

Mot C1xx (Compal)	Compal-Howto
Openmoko GTA01/02	Freerunner-Howto
Pirelli DP-L10		Pirelli-Howto