Date   : Wed, 24 Nov 2010 03:01:03 +0100
From   : rick@... (Rick Murray)
Subject: Harddisc fakery using a microcontroller

On 23/11/2010 11:33, Alan Williams wrote:

> In order to do this you need to provide a set of registers visible from
> both the 6502 and AVR side with handshaking on transfers etc.  This is
> not in the realm of the 40pin DIP PIC or AVR chips.

Perhaps I am missing something obvious here, but isn't it more or less a 
case of putting a "command" on the bus, strobing it to the device, and 
then (based upon return status signals) supplying data byte by byte?

I don't see why it wouldn't be possible for the AVR (etc) to 'read' the 
command and then accept or reply data to/from memory locations 
designated as "registers", or the scratchpad buffer in the case of disc 
sector ops.


Surely a bit of intelligent programming is better than, as you put it, 
"a small sea of TTL" which is an idea that gives me heart 
palpitations... because when you say a small sea of TTL, there's only 
one thing that comes to mind, and it isn't an XKCD strip...
   http://www.homebrewcpu.com/photo_gallery.htm


> Of course there is the added difficulty that all the BEEB side needs to
> be 5V tolerant.

I think the AT chip *is* 5V...?


> I was thinking of eliminating the host adaptor from the picture though.

I was thinking of a "fake" SCSI drive that I could just plug into my 
E01S. Whether or not or how it works with the E01 is another question...


Note to self: Must dig up Morley SCSI podule guide and read up on the
               description of how SCSI *actually* works. Looks like a
               fairly simple parallel port type system with bells and
               whistles for it being a bi-di peripheral interface... The
               main 'smarts' would appear to be on the units themselves.


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...