# HG changeset patch # User Mychaela Falconia # Date 1696148225 0 # Node ID 3ab69117b09f073a66b7b810ca1cb52d5825e5e5 # Parent 269b330ac428d11c0c7c0ba825ab5b0e49be9c50 minnie/doc/Design-spec: finished in the first pass diff -r 269b330ac428 -r 3ab69117b09f minnie/doc/Design-spec --- 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.