Disk hardware emulation, was Re: Grandfather system RTE6/VM?

From: Eric Smith <eric_at_brouhaha.com>
Date: Thu Dec 11 16:10:07 2003

I wrote:
>> Without decoding the data, it is proposed to sample the data at 50 Mbps
>> or more.

Andy wrote:
> Why so fast? You only need sample at 2x the bandwidth.

2x is the theoretical minimum; sampling at 2x isn't always adequate
in practice due to various real-world limitations.

The minimum write data pulse width spec for the WD1000 controller
is 60 ns. If we were sampling and reconstructing a sine wave with
a 120 ns period, 16.7 MHz sampling would be adequate. But that
wouldn't yield good results for square waves, and there wouldn't be
any margins. In practice, I suspect that 33.3 MHz sampling would be
barely adequate provided that no other problems arise. Operating at
50 MHz seems advisable to have reasonable margins.
Received on Thu Dec 11 2003 - 16:10:07 GMT