[time-nuts] OT: 10 MHz data capture, help

John Miles jmiles at pop.net
Sat Apr 25 11:26:28 UTC 2009


> It might make sense to layout something on the front section of
> the board.
> As long as that section isn't stuffed it won't get in the way.
> Whatever is
> likely to be most popular.
>
> Does anybody know of an inexpensive FPGA card like that?

Tom eventually went with a USBee SX board.  The manufacturer doesn't say,
but I'm guessing there's a fair bit of RAM on those boards, because they
claim to support continuous streaming at 24 megabytes/second with no data
loss.  As it turned out he had a clock line available for the NRZ bitstream,
so he didn't have to sample at 20 MHz.

I fooled around a bit with a Xylo USB board and was able to recover a
clocked bitstream at 10 MHz, but with only the 512-byte FIFO on the FX2,
there's not much time for Windows to go out to lunch.  It's probably
possible to synthesize a large-enough FIFO in the gate array to make the
process reliable.

> There are a handful of reasons why FPGA and PCI don't play
> together well.
> The main one is that old 5V PCI can generate 11V spikes from
> reflections and
> that is off scale with modern silicon technology, or at least the
> branch of
> it used in the FPGAs that I'm familiar with.

KNJN has been selling their "Dragon" PCI board (
http://www.knjn.com/?pg=cat&src=3 ) for awhile, and it looks like they just
glued the Spartan-2 chip to the bus.  Looks simple enough, if not especially
inexpensive.

They have a habit of not fully documenting their hardware in a way that
allows you to build standalone applications with it, though.  If inspired to
do anything with their hardware, make very sure the documentation is
adequate for the job.

-- john, KE5FX




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