* This design is based on the modem section of Openmoko's GTA02-MB-A6 board;
  the modem section consists of all components that are enclosed within the
  metal shieldcan footprint with reference designator SH1.  Nothing else
  besides this modem section is reused from Openmoko's PCB.

* The reference designators used in the present design are not the same as
  those used by Openmoko.  Instead, this design uses the refdes numbering
  scheme from TI's Leonardo schematics.  However, because Openmoko's design is
  clearly based on the same Leonardo, the solution is to renumber the reference
  designators in Openmoko's PCB file before using it as the basis for the
  present derived board.  A PADS ASCII version of GTA02-MB-A6 with reference
  designators suitably renumbered can be found here:

  https://www.freecalypso.org/devboard/GTA02-MB-A6_renumbered.asc

* The following 116 components of the present design correspond directly to
  the same-named components in the renumbered GTA02-MB-A6:

  C201, C202, C203, C204, C205, C208, C209, C210, C211, C212, C213, C214, C215,
  C216, C217, C218, C219, C220, C221, C223, C224, C225, C226, C253, C295, C296,
  C318, C322, C401, C402, C403, C404, C405, C406, C407, C408, C409, C410, C600,
  C606, C607, C608, C609, C610, C613, C616, C617, C619, C620, C622, C628, C629,
  C630, C631, C632, C633, C634, C648, C651, C652, C653, C654, C655, C656, C680,
  C681, C682, C683, C684, C698, D200, L401, L402, L403, L404, L405, L406, L600,
  L601, L680, Q401, Q402, R106, R204, R206, R207, R208, R209, R210, R211, R215,
  R216, R217, R251, R270, R295, R296, R328, R370, R600, R601, R604, R621, R622,
  R623, U201, U202, U301, U401, U402, U403, U404, U602, U603, X201, X202

  With a only few minor exceptions outlined in these notes, the interconnections
  between these components in the present design are exactly the same as they
  were in the GTA02-MB-A6, therefore the entire PCB layout section consisting
  of these components should be kept as unchanged as possible.

* The following 40 components are new to the present design, i.e., do not
  originate from GTA02-MB-A6:

  C306, C310, C312, C314, C315, C316, C319, C323, C330, C331, C332, C335, C363,
  J301, J302, J305, J308, J310, J311, J312, JP1, K301, K304, MIC1, Q308, R100,
  R101, R102, R103, R104, R105, R107, R322, R329, R331, R332, R338, R351, R352,
  U302

  For these components new PCB footprints need to be created; they need to be
  placed on the PCB and interconnected (among each other and to the core section
  reused from Openmoko) per the netlist given in the present package.

  The MCL (Master Component List) gives complete definitions for these new
  parts; use the datasheets for the parts listed therein to create the
  appropriate new PCB footprints.

* The final netlist for the board as a whole can be found in nostar.unet; it
  captures both the interconnections within the core section (which are expected
  to exactly match those in Openmoko's PCB layout, modulo a few explicitly
  listed exceptions) and the connections from various components in the core
  section to the peripherals added for this development board (mostly interface
  connectors).

* The netlist is currently in an ad hoc format invented by this author and used
  internally by her tools, however, because I wrote these tools, I can easily
  add a conversion step to turn this unet internal format into whatever format
  is needed for import into PADS, Altium etc if someone points me to a
  specification describing that format.

* Openmoko's modem block resides on the side of their GTA02 board which they
  designated as the bottom; that side should now be reassigned to be the top,
  i.e., the board should be flipped over.  All newly added components should be
  placed on the same side as the modem core (the new top, the old bottom) so
  that the finished board will have all of its components on one side (the new
  top) and none on the other side.

* The board outline should be rectangularized, i.e., changed from Openmoko's
  complex shape fitting their plastics to simple rectangular.  Right angle
  connectors J305 (power input) and J308 (antenna SMA) must be placed along
  edges of the new rectangular outline.

* Openmoko's GTA02 board includes microphone and speaker circuits, but they are
  not reused in the present board design.  Instead the microphone and
  loudspeaker circuits included in the present design are "new" from the
  perspective of PCB design, i.e., they don't come from GTA02-MB-A6 - they are
  based on Leonardo schematics instead.  Openmoko's audio circuits could not be
  reused because they route all analog audio signals through an external chip
  that is part of Openmoko's application processor subsystem which won't be a
  part of our FreeCalypso GSM development board.

* The specific microphone part that appears on the GTA02 PCB is no longer
  obtainable.  The present design uses a different microphone part that is
  readily available from Digi-Key, however, the new microphone part has a
  different PCB land pattern.  Therefore, the old microphone land pattern from
  GTA02-MB-A6 must not be reused.

* For the loudspeaker circuit, instead of including an actual loudspeaker part
  directly on the PCB, my circuit design includes a 2-pin header to which this
  loudspeaker is to be connected.  This way the choice of specific loudspeaker
  type does not have to be made upfront.  Some free space should be left on the
  board close to this connector (J312) so that a loudspeaker can be placed there
  and secured with double-sticky tape or similar means.

* Unpopulated resistor footprints at reference designators R401, R402 and R403
  appear on Openmoko's board in the modem section, but do not appear in the
  netlist of the present design.  They should be removed from the board.  (One
  may reasonably argue that leaving these unpopulated resistor footprints costs
  nothing and does no harm, but they are so unquestionably wrong that I could
  not bring myself to work them into my design sources from which the board
  netlist is compiled.)

* The 5 components at reference designators Q1000, Q1001, R1012, R1018, and
  R1021 also appear on Openmoko's board, but not in the present board design.
  These components comprise Openmoko's circuit for controlling Calypso modem
  power and reset from their application processor; that circuit is not
  applicable to the present FreeCalypso GSM development board and hence needs
  to be removed.  This removal will lead to R208 remaining as the only component
  in that section of the board; that resistor can be moved as makes sense given
  the new netlist for the power-on and reset circuits in question.

* 0R jumper-resistors at reference designators R1003 and R1004 in Openmoko's
  original design need to be removed and replaced with solid power traces.
  Note the two already existing separate traces emanating from C214 (former
  C1009) and going toward R1003 and R1004 - simply extend these two traces to
  reach the other ends of the removed R1003 and R1004 footprints.

* The existing PCB layout from Openmoko includes a trace in the memory bus
  section that runs from U301 (former U2000) ball F9 (2nd flash bank chip
  select) to Calypso (U201, former U1001) ball C11 (nCS4).  If possible, I
  would like to have this signal go to Calypso ball C1 (nCS2) instead, for
  memory map consistency with our future quadband designs.  The current netlist
  has this signal connected to nCS2 (ball C1).  However, if moving this signal
  proves to be too difficult (too disruptive to the layout), it can be left
  where it is, and I will change the new netlist accordingly.

* The 32.768 kHz crystal at reference designator X201 (part MS2V-T1S) physically
  has 3 pads in its PCB footprint: two electrodes and a case ground.  The
  current netlist has it as a 3-pin component.  However, Openmoko's schematics
  show it as a 4-pin component with electrodes on pins 1 and 4 and ground on
  pins 2 and 3.  I readily admit to not understanding what's going on here.
  Depending on how this component actually appears in the PCB layout, I can
  adjust my netlist accordingly to match.
