[time-nuts] FPGA protobards (was Re: Of rubidiumlifeandpiggy-bank anemia....)

[John Miles]

It's very complicated.  Without getting into the details of I2C EEPROMs and
stuff like that, the KNJN boards work by using the 8051 controller in the
FX2 USB chip to implement both the programming protocol and the
communications protocol.  They have simple example applications in C that
run on the PC and allow you to interact with various lights and buttons on
the FPGA pins.  However, the details of the 8051 programming process aren't
well-documented, so you end up having to run KNJN's programmer application
to upload their code to the (volatile) embedded 8051 before you can run your
own application code that communicates with the board.

That will have to be reverse-engineered before any true standalone
applications can be written for the KNJN boards.  It's conceivable that some
of the GNU Radio FX2 code can be applied directly to the KNJN boards; I
haven't gotten that far yet.

There are many simple FX2+FPGA development boards on the market besides
KNJN's, but without exception (as far as I can tell) they are all produced
by mom-and-pop development houses who believe, religiously, that by leaving
their programming protocols and 8051 code undocumented, they are actually
*adding* value to their products.

-- john, KE5FX

> > Right; 'program' was a poor choice of words.  My concern was more
> > about how to get data off the board.  I know it's customary to use a
> > separate JTAG connection for programming, but if you can do both
> > through the USB port, it seems like an obvious way to go.
>
> Beware.  At least some of the FPGA boards with a USB connector
> only use it
> for programming and power.  The USB signals usually go into a
> tiny micro.  It
> knows how to program the FPGA but there isn't any simple way to
> use it as a
> data path.
>
> I could easily have missed something wonderful on newer board.  I
> do remember
> being surprised when I figured that out the first time.
>
>