TTXS and Chopstx for STM32L432

[NIIBE Yutaka]

Hello,

I do some work to port Chopstx to STM32L432.  No FPU support, no drivers
other than USART, currently.  My intention of this port is not for Gnuk,
but for new project named TTXS.

It is free firmware for CCID reader.

    Tian Tian Xiang Shang - free firmware for CCID reader:
    https://www.gniibe.org/memo/development/ttxs/ttxs-hardware.html

It is not mature, but somehow works with OpenPGP card now, with
STM32F103.  I test it with OpenPGP card against Gnuk's test suite.  My
motivation is simple: While supporting OpenPGP card for GnuPG, it's good
to have less unknown factors.  Currently, my intention is to figure out
minimum feature set of CCID reader.  It is TPDU T=1 only card reader.
Perhaps T=0 support would make sense (for other cards).

Some smartcards run in "inverse convention".  In this communication, the
polarity and the order are opposite (1 is lower voltage and MSB first).
STM32L432 can support this feature, with no external hardware.  I'm
going to port USART driver (and possibly USB driver) to STM32L432 and
port TTXS to STM32L432.

Unfortunately for Gnuk, STM32L432 comes with many features.  The core is
Cortex-M4 with FPU.  And it comes with many peripherals with many
features.

In my opinion, I don't need those features for Gnuk.  After all, if we
need more features, it's better to use PC for having our private keys.

Perhaps, in future (after the first release of current TTXS), it would
be better for me to develop TTXS with FPGA.  I think that it is feasible
by something like TinyFPGA BX.
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