Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!sun-barr!cs.utexas.edu!samsung!zaphod.mps.ohio-state.edu!mips!daver!bungi.com!news
From: jcallen@maxzilla.encore.com (Jerry Callen)
Newsgroups: comp.sys.nsc.32k
Subject: Now, where was I?
Message-ID: <9012072303.AA23483@maxzilla.>
Date: 7 Dec 90 23:03:27 GMT
Sender: news@daver.bungi.com
Lines: 55
Approved: news@daver.bungi.com

Speaking of floppy controllers that I ran out of gas on...

I've been thoroughly swamped for the past six months, and I've only
just this week resumed fooling around with my pc532. With any luck I'll
have Minix up in a week or so, and then catch up on pc532 mail, and then...

...maybe get back to work on the floppy controller? I've noticed a few
messages about folks wanting to attach devices via the DUART sockets;
this tells me we have a REAL problem. George, I have no intention of
restarting the "bus wars" discussion of a year ago, but clearly people
are finding it difficult to hang devices off the pc532. Let's face it:
a raw uprocessor bus is really easy to attach stuff to, and SCSI isn't.
What _I_ think we need is a nice generic coprocessor card design that
DOES have a simple bus; conceivably this card could run a stripped down
version of Minix.

My original idea for the floppy controller was:

- some micoprocessor with at least 2 DMA channels (one for SCSI, one for
  anything else)
- DP8490 SCSI interface chip
- DP8473 floppy disk controller
- some static ram
- some EPROM
- a serial port (optional, but nice to have to talk to ROM monitor)
- a parallel port (cause everyone wanted one)
- some DRAM (I'd drop this now, since SRAM has gotten so cheap and is SO easy)

By dropping the DRAM I'm sure I could design this. The tricky part may well
be the sofware. Anyway, this could easily be used as a "generic" pc532
peripheral interface card.

The piece that I never resolved was the processor. Some possibilities:

- HD64180 (or Z180): has DMA and serial channels on-chip, but basically
  a dull, obsolete part (64K address space with simple MMU).

- 68070 (or some newer Moto part?): has DMA and serial on-chip, but
  kinda pricy, also a 16 bit bus (8 bit is easier, though I am lately
  thinking 16 is OK)

- 80188/80186/V50/whatever: plenty of on-chip peripherals, but that
  $#@ Intel architecture

- NS32CG160: 2 DMA channels, on-chip interrupt control unit. Biggest
  plus, in my mind, is instruction set compatibility with pc532, so we
  all have the development tools already. Pricy, near as I can tell...

- Other?

With any luck I'll restart this project in January. What do you folks out
there want for the processor? Any other design ideas?

-- Jerry Callen
   jcallen@encore.com