Date   : Fri, 07 Oct 1994 14:10:45 +0100 (BST)
From   : Mark Cooke <ee2015@...>
Subject: Re: Re : BBC Disks

> 
> > Hum.  I wasn't sure about exactly how I'm going to do the I/O bit.  I
> > think it may be a right royal pain to get BBC disk images into the PC. 
> 
> Too right.
> 
> > However, my initial plans were just to emulate the sector R/W's for DFS
> > and ADFS, and write a bunch of utilities in an extra rom to :
> > 
> > 1. Load an image from the PC filing system, and set it's load/exec/name
> >    addresses.  Then change to ADFS and write it out.
> > 
> > 2. 'Mount' BBC disk images. (ie swap disk images ADFS points at)
> > 
> > 3. Take snapshots of my emulator state and use these to restore the screen.
> > 
> > Any thoughts about this are welcome.
> 
> Hmm. Well, I dunno. It's a gut feeling for me that it should be a 100% 
> emulator - disks and all. However, I see what you're trying to do. No 
> point in making it difficult for us, I suppose.
Maybe I wasn't clear.  The utility rom is basically an automated way to
take stuff from the PC hard disk and stuff it into a (single) floppy image
that the sector intercepts read from/write to.
> 
> You could actually use PC filenames (I think) - they're 12 characters 
> aren't they? Intercept the OS calls maybe.
Yeh.  You can.  What do you do about load/exec addresses though.  I
considered using a separate file with this info in, which could be simpler
than trying to produce disk images.

> 
> The other idea I had would be to create a virtual HD on the PC (ie one 
> big file) and as ADFS jumps around sectors, just jump around the file. 
> This would give the BBC a floppy disk, a hard disk (and a damn fast ADFS 
> one at that!).
Hum.  Great idea.  I'll probably extend the disk image idea to large
formats at some point - probably when I have a Master emulator running.
DFS will do for now.

> 
> I think I'll stick with the idea of implementing a floppy drive. I wonder 
> if ADFS uses OS calls (and if they even exist!) to read / write to 
> sectors. This could make implementing a floppy drive very easy - you'd 
> just have to set up the PC bit to read the right sector size, etc.
>
I think ADFS does use calls (OSWORD 7F ?).  Mike Borcherds is the man to
ask - he's on the mailing list.  He has a complete (probably) set of docs
ranging from BUG, AUG to the Master guides and Econet stuff.
 
> > PS. There's a chap asking about BBC emulators in comp.emulators.misc.  I
> > posted some info about my emulator, but could not find the complete list. 
> > Could you mail it to him (and me). Ta.
> 
> I posted the list; I'll include it here as well though.
>
Cheers.
 
> +-------------------+-------------------------------------------------+
> | /-- |_| /-- | (~  | "And the driving is like the driving of Jehu,   |
> | \-- | | |   | _)  | the son of Nimshi, for he drives furiously."    |
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> +---------------------------------------------------------------------+

Mark

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