Date   : Sun, 28 Nov 2010 15:05:01
From   : heyrick.beebsoc@... (Rick Murray)
Subject: [BeebSoc] Harddisc fakery using a microcontroller

On 23/11/2010 01:03, Mark Usher wrote:

> Phil Blundell was thinking of putting a board together to do a SD card to
> SCSI 1/SASI adapter.
          ^^^^

I have not been able to find a SCSI-1 specification, but I found a SASI 
spec at:
   http://www.bitsavers.org/pdf/ansi/X3T9/X3T9.3_185_RevE_SASI_Apr82.pdf

Is this "close enough" to work?

I would imagine the timing is not terribly critical, as I've used SCSI-1 
tape streamers and they're quite a bit slower than harddiscs (well, 
except possibly that 20Mb MiniScribe!). I ask this as I was wondering 
about the feasibility of cobbling together a rudimentary emulation using 
my A5000's parallel port and user port I/O podule, to get a feel for how 
SCSI (SASI) works on the lines before considering anything like an 
MCUified version. What worries me is even with ARM code, how responsive 
must the device be? Hooking the control signals to IRQs would help, no 
doubt.

At a brief look, it seems very parallel-port-like in that the data bus 
is loaded, a signal flags this (REQ), and you (the SCSI device) ACK it 
upon reading.


Would I need to support ARBITRATION and RESELECTION? [re. p12 & p14]


Best wishes,

Rick.