[Cryptech Tech] Constant stream of USB data on Alpha's UART ports?

[Peter Stuge]

Rob Austein wrote:
> Yuri Schaeffer reports that the Alpha's serial ports seem to be
> generating a lot of USB traffic, even when the HSM is idle.  I can
> confirm this: Wireshark[*] shows a constant stream of URB_BULK packets
> flying between the host and each of the FTDI UART chips.
> 
> Is this normal?

For these FTDI chips, yes, it is normal.

Their use of USB is both redundant and wasteful.

The FTDI protocol uses a two-byte packet back and forth to poll for
data in the incoming UART FIFO.

USB hardware would already do polling if instructed to, there is zero
need to do that in software. And besides the unneccessary software
overhead, the back-and-forth bus traffic is not only useless but
actually quite annoying if you need to debug on the bus level.


> Is there something we can and should do about it?

Switch interfacing solution. ;)

The daughterboard I threw together has potential. I used essentially
the same firmware with great results in other projects, but not at
921600 speed. It's based on a firmware sample, which had many issues.

I promised to fix the firmware (I will simply rewrite it, also for
licensing reasons), and I don't intend to back down on that promise,
but haven't done so yet.

I have excitedly been watching the 3.0 reports! It has certainly
motivated me to look into this thing again.

Is there an event/meeting in the next few months?


//Peter