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From: jkurki@tukki.jyu.fi (Jouni Petri Kurki)
Newsgroups: comp.os.minix
Subject: Re: Trouble with Amiga floppies - a possible solution
Keywords: Amiga floppies MFM
Message-ID: <1990Oct6.220057.24374@tukki.jyu.fi>
Date: 6 Oct 90 22:00:57 GMT
References: <1850@Terra.cc.brunel.ac.uk>
Organization: University of Jyvaskyla, Finland
Lines: 56


(my first reply here... )

In article <1850@Terra.cc.brunel.ac.uk> eesrajm@cc.brunel.ac.uk (Andrew J Michael) writes:
>
>Having just had a good look at the AmigaMINIX sources, I'm not entirely
>surprised that there are problems with floppy disks.  This is NOT meant as
>a criticism of AmigaMINIX (quite the opposite, it's VERY clever).  It's more
>a comment on the Amiga's hardware design.

I haven't purchase Amiga minix yet, because I'm looking for ready made
HD support (Commodore 2090A). I must admid that I probably can't do it
right now myself. :-)

As I have not seen Amiga Minix sources, I can't really know about this 
particular port of Minix, but I have read original book (Tanenbaum) and
IMHO good floppydriver can be done with reasonable knowledge of Amiga 
hardware.

>From looking at the code, it seems that the Amiga doesn't understand sectors;
>it only knows about tracks, and raw ones at that.  To simulate a normal MFM
>disk controller, some natty software in the AmigaMINIX kernel manufactures
>what looks like an MFM track, complete with sector gaps, headers and CRCs and
>gets the Amiga hardware to write it out to the floppy as a raw track.

Amiga hardware is a bit unique here. But there has been at least four
commercial,and couple PD programs that can read/write PC formatted 
720k floppies. Crossdos (Commercial, Consultronics) and MessyDos (PD,
Olaf Siebert) even have MS-dos compatible filesystems for Amiga, so 
you can directly access all files from PC 720k disks. 

Besides full-track caching shoud make disk I/O quite a lot faster compared
to single sector read/write. It needs more code than simple diskcontroller
chip (as found in Pc) but it's allso much more flexible. I belive these 
troublsa are some minor features (bugs?) in Amiga-minix software, and will
be fixed quite soon (I hope). 


Well... these are my thougths anyway...

Jouni Kurki



PS. Is there good English spellchecker in Minix? ;-)







-- 
=============================================================================
Jouni Kurki                             Internet:      jkurki@tukki.jyu.fi
             ( I need to write something clever here )