Date   : Tue, 06 Jul 2004 16:09:45 +0100
From   : Richard Gellman <splodge@...>
Subject: Re: Acorn Winchester unit

Mike Tomlinson wrote:

>In article <5035133C-CE03-11D8-AADD-000A27B4860C@...>, D. G.
>van der Pol <danielg@...> writes
>
>  
>
>>Does this sound familiar, or did I overlook something. I used HDForm 
>>first to format, them I found Superform somewhere on the net. These 
>>programs don't seem to care that my drive is using 512bytes/sector
>>    
>>
>
>IIRC, they don't issue a Format Unit command, but just clear sectors and
>lay out a filesystem map.  Hence the sector size is not changed.
>
>  
>
>>but 
>>as soon as I start to save data on the drives, I run into problemes 
>>that invalid data is read from the disk.
>>    
>>
>
>Not surprising, if ADFS is expecting 256 bytes to be returned from the
>drive in reply to a Read Sector command, and 512 are returned instead.
>  
>
I may have explained this before, but ADFS actually does "lazy 
commands".  Presumably this save ROM memory space, but basically instead 
of correctly discarding the excess data and waiting for the bus state to 
change like a good little SCSI host, it receives the 256 bytes its 
after, then switches into "status receive mode", and cunningly 
interprets byte 257 as status. Being non-zero, this makes the ADFS do 
its nut and report a read error.

Writing is also amusing. ADFS only chucks out 256 bytes, whereas the 
drive is expecting 512. Fortunately, when you write an even number of 
sectors out, you fill up the 512 bytes. Thought whats going on with the 
remaining data the SCSI drive is expecting is anybody's guess.

Much easier to format the drive to 256-byte sectors really.

-- Richard