Date   : Tue, 06 Jul 2004 08:53:58 +0000
From   : <andrew.chesterton@...>
Subject: Re: Acorn Winchester unit

> 
> From: D.G.van der Pol <danielg@...>
> Date: 2004/07/05 Mon PM 09:51:27 GMT
> To: bbc-micro@...
> Subject: Re: [BBC-Micro] Acorn Winchester unit
> 
> 
> Op 5-jul-04 om 22:58 heeft Johan Heuseveldt het volgende geschreven:
> 
> > Hi all,
> >
> > On Mon 05 Jul, Mark Usher wrote:
> >
> >> There are usually parameters in one of the command blocks on the SCSI 
> >> unit
> >> that you can set to the sector size. Just look at the SCSI spec, I 
> >> can't
> >> remember off hand just at the mo which one. Usually drive specs will 
> >> tell
> >> you if the drive has the capability or not, most of the older SCSI-1 
> >> drives
> >> do.
> >
> > And others seem - I feel - to be optimistic too, for connecting a SCSI
> > drive directly to the Host-Adapter, and let it work with ADFS.
> >
> > I don't want to spoil everyones appetite, but generally speaking this
> > is /not/ possible.
> >
> > Why? Because SCSI drives won't allow a low level format, and there is
> > no way to use a logical model of 256 bytes sector on top of the 
> > physical
> > 512 bytes per sectors /in/ the drive.
> > But you can do that in software of course!
> > But you should write something yourself though, as it is not easy
> > to patch ADFS: recalculate blocknumbers, and handling 512 bytes
> > reads/write on low level before ADFS Filer is involved, which needs
> > extra memory/code.
> >
> > If it was /that/ simple to connect a SCSI drive to the host adapter
> > directly, it would be widely in use for twenty years now! :-) I think
> > it's a bit pedantic to assume this is an easy task, which no one has
> > discoverd so far! :-) Hm, perhaps it's me who's pedantic now! :-|
> >
> >
> > Is this all? No it isn't, There are a few exceptions!
> >
> >  1: Try to find the Seagate SCSI drive: ST157N (the 'N' is vital!)
> >
> >      as this drive /does/ allow a low level reformat with the 
> > desperately
> >       needed 256 bytes per sector; it then fully works under ADFS!
> >
> >  2: The (old) Syquest removable 44 MByte is also known for allowing a
> >      physical reformat to 256 bytes per sector.
> >     Not sure about the 88 MByte.
> >
> >
> > Another way is finding the original info about the -4000 board, as 
> > this is
> > quite intelligent. Perhaps a logical 256 bytes per sector is supported?
> >
> > I know someone with those docs. I'll ask him to borrow those for 
> > scanning in.
> >
> >
> > I hope this is of some help to you all?
> > Johan
> >
> 
> Yes, this is very helpful. I was indeed assuming it was that simple to 
> connect a scsi-drive to the host adaptor board. Point is I have an 
> awful lot of scsi drives from old macintosh computers.
> 
> I did read about some scsi drive that was capable of reformatting in 
> 256 bytes/sector. Could indeed have been that Seagate you mentioned. 
> Most drives I have are old Quantum drives ranging from 20Mb to 4Gb. 
> Those don't work at all, I tried really advanced scsi formatting 
> programs which give you almost low-level control over the drive, even 
> selecting the bare scsi-commands and tampering with codepages.
> 
> So I almost gave up until you mentioned the last thing: the Syquest 
> 44Mb drive. I have also quite a few of those with boxes of discs that 
> is. Next weekend I will give that a try. I might use a mac to reformat 
> them to 256 bytes/sector and then try again.
> 
> As far as I know, the formatting programs on the Master are not that 
> advanced. They access the drive as a block device and as long as you 
> tell them how many tracks/heads/sectors there are to be found on your 
> disc, they just calculate how many blocks they can use for the Master 
> 'partition'.
> 
> But as long as my Master with Harddrive does not work, I might as well 
> be wrong. It would be so cool to have a working harddrive on my 
> Master....
> 
> Thank you all very much for you comments. I am always interested in 
> more suggestions & maybe just plain corrections.

If anybody is local to the Midlands in the UK and wants to check the BBC
- SCSI accesses, I have an Ancot SCSI bus analyser that I am prepared to
lend out.

I don't have the BBC hardware or the time at the moment to do it myself,
but it is something that I have been thinking about for a while now.

One possible project that I have been thinking about would be using an Altera 
FPGA to replace the Winchester interface board. This would be able to sit 
between the 1MHZ bus and the SCSI device(s). It may also be powerful enough
to do some address translation and cope with the 256/512 bytes per sector
problem and alow 2 BBC writes to 1 SCSI disk sector.

Can somebody invent a 36 hour day please, then I might get time to do things
again....

Andrew.

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