TI's primary development platform for TCS211 firmware was D-Sample - see our
D-Sample article for explanation of our current limited support for that target
in FC Magnetite - but they also had another platform called Leonardo.  The
primary difference is the RF section: D-Sample had Clara RF (the one for which
we lack support), whereas Leonardo was TI's reference platform for Rita RF and
for the complete Calypso+Iota+Rita chipset.  Another major difference is that
D-Sample was a single stable platform, whereas Leonardo was made in a
bewildering assortment of different variants.

We (FreeCalypso core team) never succeeded in getting our hands on a real
TI-made Leonardo board of any variant, but we do have a Leonardo build target
in FC Magnetite for two reasons:

1) Adding this build target was trivial: our starting hw target for which we
   got our original starting-point fw was Openmoko's embedded GSM/GPRS modem,
   and that modem is a very close derivative of Leonardo.  The only firmware-
   affecting diff between Leonardo and OM's modem is FIC/OM's reshuffling of
   TSPACT control lines for their triband RFFE; producing a build configuration
   with these TSPACT control signals put back into their original Leonardo
   arrangement became trivial once our reconstruction of tpudrv12.c from
   disassembly of tpudrv12.obj reached production quality.

2) We are currently evaluating a certain third-party (non-TI) development board
   which strongly appears to be a very close derivative of Leonardo, even closer
   than Openmoko.  We are hoping to get one of these boards into Mother
   Mychaela's lab some time in 2020-01, at which time we will try running our
   Magnetite-Leonardo fw on it.

Supported Leonardo variants
===========================

RF bands: there were several Leonardo variants with full quadband RF using Epcos
M034F FEM, and there were several more variants with artifically restricted RF,
using a dual-band/single-region FEM and supporting only the two EU bands.  The
two versions should be firmware-compatible according to our available schematics
(the same TSPACT signals are used for Tx control), thus our Magnetite-Leonardo
fw should run on any Leonardo variant that matches any of our known schematic
versions at least in the principal aspects.

Flash memory: our Magnetite-Leonardo fw supports the following flash chips for
FFS:

4 MiB: Fujitsu MBM29DL320FB or MBM29DL320FT
8 MiB: Am29DL640G or its Fujitsu equivalent, or any MCP containing this flash
16 MiB: Spansion PL129J or its AMD predecessor, second bank on nCS2

If anyone finds a Leonardo variant with some other flash, it may not be
supported out of the box - but our included FFS configs for the Leonardo target
come directly from TI's original TCS211 version (it is highly unlikely that OM
changed anything other than adding their Samsung flash), thus we support
everything that TI's own TCS211 supported out of the box.

Memory size limits
==================

The linker script template we use for target leonardo has memory region size
limits set as follows: 8 MiB of flash, 2 MiB of XRAM and 512 KiB of IRAM.  If
you are working with a Leonardo or Leonardo-compatible board that has smaller
flash or XRAM, or has a Calypso Lite chip with only 256 KiB of IRAM, then you
have to manually ensure that you stay within your actual memory limits, as you
won't get a failing link unless you exceed the larger linker script limits.

If you are building a modem-only fw configuration (l1reconst or hybrid), it
will fit into under 3 MiB of flash (fitting into a 4 MiB flash chip together
with FFS), 512 KiB of XRAM and 256 KiB of IRAM, so you are safe unless you are
going to add a lot of your own code or data space.  But if you are going to
build a UI-enabled fw config (2092 or hybrid-ui), then you will need at least
an 8 MiB flash chip (won't fit into a 4 MiB chip together with FFS) and at least
1 MiB of XRAM.  So far all of our configs fit into 256 KiB of IRAM.

Different Calypso chip versions
===============================

If you specify the build target as just leonardo, your fw will be configured
and built for the leonardo-dsp36 target.  If you actually need leonardo-c05b or
leonardo-dsp34 because your board has an older Calypso chip version on it, then
you will need to specify the build target as just stated - see the
Calypso-version-override article.