> From: Emanuel Stiebler
> If I would do it again, it would be USB only with some sd-card slots.
Exactly our plan (although the USB is left until after we get the SD running).
> USB with 480MHz is fast enough
I think our plan was to skip that speed, and go with the next one down, on
the grounds that the analog part at that speed would be too tricky for us.
> the old 3v3 level, spi-derivative is very simple to implement. The
> 4-bit mode takes a little longer
I think we're using the SPI at the moment, not the 4-bit (we discussed both,
but I _think_ we went with the one-bit to start with), but I could be wrong -
Dave will hopefully pipe up if I blew that one.
IIRC our reasoning was that the SPI was the very simplest one to do, for an
initial implementation; if we later need the speed, and go to the 4-bit, all
the init/etc will already be working.
(That's the general approach I prefer for prototyping - get the very simplest
possible thing working, then add things. That seems to be better, overall;
probably because i) the first stage is easier to debug, because you're dealing
with the least complicated possible system, and ii) when adding things, you
know the rest of the system is functioning, so any problems have to be in the
piece you just added.)
>> (Of course, that issue we had with noise, and the wierd latching
>> inputs, made it even more painful...)
> Did you wire-wrap this thing?
Yes (for one card out of two - below), but that wasn't the problem.
The problem is that we're using two cards (one to plug into the QBUS, and one
with the FPGA on it - surprise, surprise, nobody makes an FPGA protyping card
that plugs into a QBUS :-), and the two are connected with a cable; it was
the cable that was causing the noise (cross-talk - we neglected to put a
ground line between each pair of signal lines).
Noel
