On 2017-08-04 14:18, Noel Chiappa via cctalk wrote:
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,
Probably sufficient for a start ...
> on
the grounds that the analog part at that speed would be too tricky for us.
No, it isn't.
> 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.
You use container files in fat16, or simply 1:1 block mapping?
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.
Sure.
> 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).
I agree some how with your approach, but it leads to debugging of
issues, you wouldn't have on real boards ...
