FCDEV3B update

[Mychaela Falconia]

Hello again everyone,

Further progress on the FCDEV3B: the people at Technotronix (the
assembly shop I'm going to use) got back to me and said that pcbcart's
proposed panelization is OK.  I relayed this approval to pcbcart, and
pcbcart folks said that they are now starting production.  Finally!
If we go by the 20 working days lead time we paid for, the PCBs should
be back some time in the second half of March.

On the BGA reballing front, the bubble mailer with the parts, a check
and some accompanying order notes will go out to the reballing company
on Tuesday, Feb 21 - this Saturday will be the soonest I can put it
together on my end, but the postal service here won't be open until
the following Tuesday.  The BGA reballing company's terms say 3 weeks
turnaround time after the receipt of the order and all materials, so
again we are looking at late March for everything to come back.

I now need to work on preparing the serial cable.  When we get the
boards populated with parts and power them up (I already have the
power cable which I made back in 2015 for powering the historical
souvenir TI D-Sample board we've got - our FCDEV3B has the same DC
power input connector as TI's historical development boards), the very
first thing we'll need will be the Calypso UART connection for talking
to the Calypso internal boot ROM, hence I need to make the necessary
preparations.

Our FCDEV3B has a 5x2 pin header on which both Calypso UARTs are
brought out without any level shifters - 2.8V native, but everyone
else connects 3.3V signals to them, hence we'll do likewise.  My plan
has been all along to use an off-the-shelf FT2232 board as the serial
interface for our FCDEV3B.  FT2232 is a USB to dual UART adapter,
i.e., a single USB device turns into two UARTs; there are FT2232D and
FT2232H variants.  There are many vendors who make FT2232D or FT2232H
breakout boards; these boards provide a USB mini-B connector for
PC/laptop connection on one side and all FT2232 user interface signals
brought out to header pins on the other side.  The adapter I plan on
using myself is an FT2232D board from PLDkit
(http://pldkit.com/other/ft2232d-module), I have a couple of them on
hand already, but to other people who are going to get FCDEV3B boards
eventually, feel free to use whichever adapter you like - your
preferences don't have to be the same as mine.

But how will the FCDEV3B connect to the FT2232 breakout board?  I plan
on making a special cable as follows:

* Main body of the cable: flat ribbon cable with 10 conductors of the
  multicolor kind, standard wire colors going BROYGBVGWB from pin 1 to
  pin 10;

* On the FCDEV3B end, crimp a 5x2 pin IDC female receptacle onto the
  ribbon cable, to mate with the 5x2 pin header on the board;

* On the FT2232 breakout board end, split the ribbon cable into 10
  individual wires and terminate each wire onto a single-pin female
  socket that mates with a single discrete male header pin.  Using a
  chart of which wire color corresponds to which UART signal, manually
  connect the individual female pin sockets to the header pins on the
  breakout board.

The above solution is not perfect by any means, but it is the best I
can currently think of without building our own custom FT2232 adapter
board.  Building a custom FreeCalypso USB-serial adapter board is
something we can definitely do in the future, but in the short term we
need a quicker solution, hence my cable hack outlined above.

Right now I need to scrounge up all of the necessary materials for
making this cable, and I am hoping to have one cable made before the
PCBs and the reballed BGAs come back.  The PCBs are panelized with 4
boards per panel; unless something changes, my current plan is to do
the first assembly run on two panels, thus we'll have 8 boards in the
very first batch.  I will need to test all 8 boards, but I should be
able to do it with just one serial cable and just one FT2232 adapter
board - I'll be testing the 8 FCDEV3B boards sequentially, not
simultaneously, so I'll just unplug the cable from one board and plug
it into the next.  Then later when it's time to ship boards to other
community members and to those who have claimed theirs through
crowdfunding contribution, I will need to make more of these serial
cables so we'll be able to include one with each shipped board.

We have enough parts for a total of 20 boards, and the OSP finish on
the SMT pads on the PCB has a limited shelf life, so we'll need to
have all 20 boards assembled fairly soon-ish, but I plan on doing a
split build of first 8 boards (2 panels), then the other 12 boards
(3 panels) in order to reduce the risk of loss to bad parts or
population mistakes.

Exciting times ahead - stay tuned!

Mychaela aka The Mother