Date   : Sat, 11 Mar 2006 19:00:46 +0000
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: 6502s and SASI/SCSI.

Jules Richardson <julesrichardsonuk@...> wrote:
> > Now ADFS (and the torch software) can use 7 device IDs
> 
> it can? I think original ADFS expects to be talking to a single device on
the
> bus, and I'm not sure that it sends a device ID (or possibly it does, but
it's
> hard-coded to always be 0?)
 
ADFS can access up to eight devices. Four of these always access
floppy drives. The other four access hard drives, if present. See
http://mdfs.net/Info/Comp/BBC/ADFS/HardDrive
 
ADFS sends a SCSI command block with the combined drive and sector
number in big-endian format. Essentially, the OSWORD &72 control
block contents:
 
  XY+ 5  Command
  XY+ 6  Drive+Sector b16-19
  XY+ 7  Sector b8-b15
  XY+ 8  Sector b0-b7
  XY+ 9  Sector Count
 
So, drive numbers 4,5,6,7 are never passed to the SCSI system as
they are implemented by the floppy control code.
 
The IDE patch allocates the four hard drives as follows:
 
Drive 0   IDE device 0, first 512M
Drive 1   IDE device 0, second 512M
Drive 2   IDE device 1, first 512M
Drive 3   IDE device 1, second 512M
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
RISC OS Choices System - http://mdfs.net/Software/RISCOS