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+Sony Ericsson J100 target support in FreeCalypso
+================================================
+
+SE J100 is the last Calypso device target of OsmocomBB origin to be added to
+FreeCalypso, joining the already-supported Mot C1xx and Pirelli DP-L10.  This
+target is really not interesting at all on its own merit, instead it has been
+added to FC Magnetite for testing purposes: to verify that we are able to drive
+this J100 variant of Compal's RFFE and produce correct RF Tx output as observed
+with our CMU200 instrument.
+
+Despite being a Sony Ericsson rather than Motorola product (slightly different
+case design, totally different battery and accessory connectors), in core
+technical terms this SE J100 phone is still Compal, same as Mot C1xx.  It is
+technically closest to Mot C139, with only a few differences:
+
+* The display is different: same 96x64 pixel color, but a different model
+  requiring a different driver;
+
+* A ringtone player chip is used instead of the Calypso-driven buzzer;
+
+* There are a few differences in GPIO setup, in TSPACT signal usage for RF Tx
+  and in some RF Tx parameters (APC offset and Tx ramp templates) stemming from
+  the use of a slightly newer RF PA, such that a firmware image built for Mot
+  C139 or C11x should not be run on the J100, even if the LCD and the buzzer
+  are don't-cares.
+
+If you have one of these phones and wish to run FreeCalypso on it, follow the
+procedure for Mot C139 in C1xx-Howto, with the following differences:
+
+* You need to build a firmware image specifically for the j100 target
+  (./configure.sh j100 hybrid-vpm), don't flash a c139 or c11x build.
+
+* Only the VPM configuration is available, not the proof-of-concept UI - the
+  LCD driver for the latter configuration exists only for the Mot C139 LCD,
+  not for SE J100 or any other C1xx.
+
+* It is not certain at all whether the battery charging configuration we have
+  for Mot C1xx is correct or not for SE J100 - see further below.
+
+Serial connection difficulty
+============================
+
+Connecting the serial interface (the obvious prerequisite before one can do any
+kind of firmware hacking) is a lot more difficult on the SE J100 compared to
+Mot C1xx.  Following Sony Ericsson's product line, this J100 phone does not have
+round-jack headset or charger connectors, instead all accessories (charger,
+headsets, Calypso UART access) are connected through a multi-pin connector (12
+pins to be exact) that was used by SE across their product line.  While there
+exist a number of "cottage industry" vendors who make ready-to-use serial cables
+for the kind of headset jack found in Mot C1xx phones, there does not appear to
+be anyone making comparable cables for SE J100, thus the only way to play with
+one of these phones is to construct the necessary serial cable yourself.
+
+The pins on SE's proprietary accessory connector which carry Calypso UART RxD
+and TxD on the J100 are the same pins which carry USB data lines on some other
+SE phones which (unlike J100) have an official data services / computer
+connection function, thus there are two ways to hack together Calypso UART
+access on the J100:
+
+Option 1: you can take a Sony Ericsson (or clone) USB-to-phone data cable and
+mutilate it: cut off the USB end, split out the little wires and solder them to
+your choice of 3.3 V USB-serial adapter.  This is the route that was taken by
+this author (Mother Mychaela), and when I did it, I ran into a nasty little
+problem: the wires inside the cut-apart SE-clone USB-to-phone cable are
+extremely thin (can't be any thicker than 28 AWG, and seemed to be even thinner
+than that), and the solder contraption feels like it is barely holding, like it
+is going to fall apart at any moment.
+
+Option 2: you can take the same SE (or clone) USB-to-phone data cable, but
+instead of mutilating it, connect it to another custom contraption: if you can
+find a USB female-A connector part to which you can solder your own wires (or
+cut apart some other cable that terminates in a USB female-A socket), make a
+cable contraption consisting of this USB female-A on one side (into which you
+insert the unmodified SE cable) and your choice of 3.3 V USB-serial adapter on
+the other end.  I still have one more SE-clone data cable which I haven't cut,
+so I might try this approach.
+
+For your choice of 3.3 V USB-serial adapter, you should definitely pick either
+FT232R or CP2102, so you can use GSM-specific high baud rates (GSM-specific
+because they derive from the 13 MHz clock) to transfer flash dumps and firmware
+images.
+
+Battery charging problem
+========================
+
+Another problem stemming directly from SE's accessory connector arrangement is
+that it is very difficult to connect both a charging power source and Calypso
+UART access at the same time.  At first I thought it was completely impossible
+(there is only one accessory connector on the bottom of the phone), but then by
+pure luck I acquired an unusual kind of SE charging adapter: this rare adapter
+has a pass-through mechanical design, such that one can plug this charging
+adapter into the phone and then piggy-back another accessory into it!  However,
+this kind of SE charging adapter is super-rare, and I haven't played with mine
+yet because it has Europlug pins (not USA plug) on the AC power end, and I
+haven't got around yet to acquiring the requisite AC plug adapter.
+
+Connecting both the charging power source and the Calypso UART at the same time
+is important for two reasons:
+
+1) For me as the FreeCalypso developer, that is the only way I can develop and
+test the charging configuration for this phone model.
+
+2) For "end users" of the voice pseudo-modem FreeCalypso fw configuration on
+this target, if you have no serial connection, you have no way of seeing how
+your charging progresses, as there is no LCD driver and the display stays dark
+and non-functional.
+
+Because we don't have working battery charging on this SE J100 target yet, the
+only safe way to play with this target at the present moment is to have two of
+these phones (or another phone of a different model that takes the same
+batteries), and keep one phone fully intact with its original fw so it can be
+used to charge batteries when the FC-converted phone runs its battery down.