--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mmtb1/README	Mon Oct 21 00:53:38 2019 +0000
@@ -0,0 +1,59 @@
+MMTB1 is a Modem Module Test Board intended for testing and exercising Huawei
+GTM900 and FreeCalypso FCM40 modem modules.  Specifically, the following two
+usages are envisioned:
+
+1) When MMTB1 is first built, it will be used with GTM900-B and possibly with
+   GTM900-P modules.  MMTB1 will allow the combination of FC firmware on GTM900
+   hw to be exercised properly, and then the combination of MMTB1+GTM900 can be
+   officially recommended to community members seeking to play with FreeCalypso
+   fw.
+
+2) When FCM40 gets built much later, MMTB1 will be used for production testing
+   and bring-up of first FCM40 modules.  MMTB1 is more GTM900-oriented and
+   therefore won't be ideal for exercising FCM40 modules, but it will be
+   sufficient for basic bring-up, missing only microphone and MCSI interfaces.
+   Once that milestone is passed, a new MMTB version will be created
+   specifically for FCM40 functional demonstration.
+
+MMTB1 is going to break out the FPC interface of GTM900 as follows:
+
+* The power input connector will be the same as on FCDEV3B.
+
+* The two Calypso UARTs will be brought out to a 10-pin header in the same
+  pinout as on FCDEV3B, with GPIOs 2 & 3 (DCD and DTR) brought to the two pins
+  which are unused and unconnected on FCDEV3B.
+
+* PWON and RESET pushbuttons will be provided on MMTB1 just like on FCDEV3B, as
+  well as a green power-on LED.  The LED will be controlled by the Vio output
+  coming out of the modem module, but without loading the Vio rail itself,
+  using raw VBAT and the same MOSFET circuit as on FCDEV3B.
+
+* There will be a SIM socket on the MMTB1 itself.
+
+* There will be two 2-pin headers for analog audio, one for the earpiece
+  speaker and one for the microphone, connected to the corresponding GTM900
+  interface pins.
+
+The following GTM900 interfaces will NOT be brought out or exercised in any way:
+
+* ADIN1 (general-purpose ADC) connection on pin 14;
+* GPIO1 connection (DSR output) on pin 16;
+* GPIO0 connection (RI output) on pin 17;
+* Vbackup connection on pin 30;
+* LPG output on pin 32;
+* AUXO secondary audio output on pins 33 & 34;
+* AUXI secondary audio input on pins 39 & 40.
+
+These interfaces have been omitted because they are not essential for the
+intended application of exercising FreeCalypso fw on GTM900 hw, because I am
+lazy (not interested in doing more PCB layout work than I have to) and because
+I couldn't find a suitable MOSFET to implement another LED circuit for LPG.
+
+No pull-up or pull-down resistors are provided on UART inputs to the Calypso,
+including GPIO3 serving as the DTR input: I will always have all of the UART
+signals connected to an FT2232x dual UART adapter (PLDkit FT2232C/D breakout
+boards at first, then later our own DUART28) by way of a custom-crimped cable
+that mates with the 10-pin header as a solid piece, leaving no possibility of
+any UART signals being left unconnected.  If anyone does not like this
+arrangement, feel free to make your own alternative GTM900 breakout/interface
+board.