On Sat, Nov 02, 2013 at 05:25:05PM -0000, Robert Jarratt wrote:
I have been mulling a project to emulate MFM disks (DEC
RD53 and RD54 in
particular) at the disk-to-controller interface.
You're part of a long tradition of mulling!
Looking for recommendations for a suitable
microcontroller that does not
cost the earth ...
I never miss a chance to gush about the XMOS XS-1 chips. They're great
for this kind of thing -- once you're down into things that happen a few
dozen ns apart you'll definitely want to use assembly language, but it's
not a bad architecture once you get over how C-centric it is. The main
down side is that XMOS is proud of their tiny packages so you'll need
paste solder. But
oshpark.com is cheap and a toaster oven works nicely
for soldering. The chips themselves are mostly under US$20 and have a
very nice architecture for handling events. And they're hyperthreaded
in hardware so you can have one thread watch the RQDX3 side and another
handle the SD card and they both execute instructions no worse than once
every two clocks (if you're fully loaded at 8 threads -- faster if not),
so it's easy to keep up w/o driving yourself crazy.
Someone (was it Emanuel maybe?) suggested doing the emulation at the
level of the HD controller chip (I forget, is it an SMC part?) on the
RQDX3 board. Assuming you can find the data sheet, doing a register-level
emulation might *really* loosen up the timing quite a lot (hundreds of
nanoseconds to respond). Plus then you'd be dealing with cooked bytes
instead of raw flux transitions so you might be able to put something
more useful on your SD card (like plain old .DSK files, so it'd be easy
to insert/extract files with the SD card plugged into another computer
w/o having to hack the low-level format).
John Wilson
D Bit