Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP 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. -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dave Haynie {caip,ihnp4,allegra,seismo}!cbmvax!daveh Why look here for inspiration, when its all around you anyway. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~