[Cryptech Tech] USB interface

[Rob Austein]

Well, I'm not technically competent to have an opinion on the Amtel
SAMD11, so I'll assume you've done your homework there.

I have no great love for the FTDI chips, and would not mind replacing
them with something better, but I do have two concerns:

1) As you note, somebody would have to write software.  We're on a
   very tight budget at the moment, with fairly aggressive deadlines
   (Joachim can speak to this better than I), so I'm concerned that if
   we jump off this particular cliff we must be able to follow through
   to completion and produce a usable board on schedule.

2) I don't yet really understand what the data transfer between the
   SADM11 and the STM32 would look like with your proposal.

   If I'm reading correctly, you are *not* proposing to break from our
   previous decision to avoid implementing USB itself in the STM32, so
   we can keep all USB protocol outside the security perimeter (for
   which I thank you, since I think recall that you have personal
   opinions on the subject which you are suppressing for the sake of
   consensus).  But that leaves me puzzled as to what the data
   transfer does look like from the STM32 side with this proposal.
   Does software on the STM32 still just treat it as a fast UART?

   Need to understand this to make any kind of informed decision about
   security properties, so please forgive if this is a dumb question
   or one that you think you already answered.