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Path: utzoo!mnetor!seismo!rutgers!cbmvax!daveh
From: daveh@cbmvax.cbm.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: Re: Great big huge floppy disk?
Message-ID: <1164@cbmvax.cbmvax.cbm.UUCP>
Date: Tue, 23-Dec-86 11:28:54 EST
Article-I.D.: cbmvax.1164
Posted: Tue Dec 23 11:28:54 1986
Date-Received: Tue, 23-Dec-86 21:49:39 EST
References: <736@vaxb.calgary.UUCP>
Organization: Commodore Technology, West Chester, PA
Lines: 24

> Summary: Sorry won't work

> Does anybody know what [floppy] controller chip the Amiga uses? If it is an 
> FDC765A or equivalent, has anybody tried an FDC7265 which is supposed to 
> get 20% more storage and be "completely software- and pin-compatible"?

Sorry, you're out of luck.  The Amiga floppy disk is controlled by a 
section of the Paula custom chip.  This chip is told by the 68000
what track to read or write, then it goes about reading or writing 
during a specific DMA slot assigned to disk I/O.  You always read full
tracks with this controller.  Once a track has been read in by Paula,
it must be decoded (Paula reads raw MFM data).  The blitter is used to
decode this, usually a sector at a time, and it achieves this decoding
in one blitter pass (though as I recall, it takes three passes to encode
the data).  Because of all this, floppy disk buffers are constrained to
reside in Chip memory.  

-- 
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Dave Haynie	{caip,ihnp4,allegra,seismo}!cbmvax!daveh

      Why look here for inspiration, when its all around you anyway.

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