--- a/minnie/doc/Design-spec	Sun Oct 01 07:01:56 2023 +0000
+++ b/minnie/doc/Design-spec	Sun Oct 01 08:17:05 2023 +0000
@@ -334,9 +334,86 @@
 
 2.5. RF plumbing
 
+The RF interface on FC Tango module is a microcoaxial connector of a type
+compatible with Hirose U.FL and Sunridge MCB2 series, but a GSM MS development
+board needs to bring out its RF interface on an SMA female connector.  The plan
+for FC Minnie is to use the same approach as was successfully implemented on
+FC Caramel2: a microcoaxial cable assembly from Sunridge that goes from an
+MCB2G plug to an SMA connector that has PCB mounting legs only for mechanical
+securement and grounding, while the RF signal never passes through the main PCB.
+
 2.6. SIM socket
 
+The SIM 2FF socket on FC Minnie will be of the same hinged type as featured on
+FCDEV3B and Caramel2 boards.  The placement and orientation of this socket on
+the board will need to be chosen so that it will work conveniently with SIMtrace
+FPC cables; FCDEV3B is good in this regard, but Caramel2 is not.
+
 2.7. Analog audio
 
+Only the main analog audio channel will be brought out, not auxiliary.  The main
+audio channel will be brought out on a 2.5 mm TRRS jack in the pinout that was
+originally established by iWOW with their DSK and has since been adopted by
+FreeCalypso, same as on FC Caramel2.  FreeCalypso HQ has a large batch of
+FC-HDS4 headsets that have been custom-made for us in this pinout, hence it
+makes no sense to implement any other arrangement.
+
 2.8. Digital audio
 
+Calypso MCSI is a PCM interface to the DSP part of Calypso that can be
+configured (using the standard facilities of DSP ROM code plus TI's official
+patches) to carry digital voice during calls, in 13-bit linear PCM sample
+format, 8000 samples per second.  This interface was first brought out and
+experimented with on FCDEV3B, but it is also brought out on FC Tango module.
+This interface will be brought out on FC Minnie board on a 5-pin header, in the
+same pinout as on FCDEV3B.
+
+The Mother of FreeCalypso has a plan to produce a gateware design for the common
+Lattice iCEstick FPGA board that will turn this Icestick into an interface
+adapter for Calypso PCM voice, ferrying digital PCM samples to and from a Linux
+host by way of FT2232H UART channel on the Icestick itself.  In this plan the
+PCM interface will be connected with jumper wires directly from the Icestick
+board to the MCSI header on FCDEV3B, FC Minnie or FC Caramel2.
+
+3. Production notes
+
+3.1. Manufacturing and test process overview
+
+FC Minnie boards will be assembled at Technotronix in Anaheim, California, USA
+and then production-tested at FreeCalypso HQ.  The assembly performed at
+Technotronix will include permanent mounting of a Tango module onto each Minnie
+board, whereas the subsequent production test process at FreeCalypso HQ will
+include the following steps:
+
+* FT2232H EEPROM programming;
+* Loading FreeCalypso firmware into Tango module flash;
+* Preening FFS for FC Tango firmware and for FC Minnie pinmux config;
+* Testing the GSM RF tract in all 4 bands with a CMU200;
+* Testing the SIM socket by inserting an FCSIM1 card and verifying correct
+  SIM communication;
+* Testing the analog audio interface by inserting an FC-HDS4 headset and
+  commanding the firmware to generate a beep;
+* Other minor hardware tests as feasible.
+
+3.2. Permanent coupling of Minnie board and Tango module
+
+FC Tango modules are not meant to be casually swappable once mounted on an
+application board such as FC Minnie:
+
+* The module features 4 grounding legs which must be soldered; these grounding
+  legs are essential, as they carry power supply return current during GSM Tx
+  bursts.  The need for soldering and desoldering should already be seen as a
+  deterrent to casual (unnecessary, just for the heck of it) module swapping,
+  but given that many hackers have absolutely no difficulty with soldering,
+  other factors should be considered too:
+
+* The fine-pitch board-to-board connector with 80 pins is extremely delicate,
+  and can be easily damaged by unnecessary mating and unmating cycles;
+
+* The microcoaxial connector for the RF interface is likewise very delicate and
+  subject to the same considerations.
+
+If a *legitimate* need to remove and replace the Tango module does arise (for
+example, if some component inside the module goes bad and you need to either
+repair or replace the Tango module), it can certainly be done - but it should
+NOT be done casually, just for the heck of it.