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Path: utzoo!watmath!clyde!rutgers!cbmvax!grr
From: grr@cbmvax.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: (actually, disk details)
Message-ID: <1371@cbmvax.cbmvax.cbm.UUCP>
Date: Mon, 9-Feb-87 01:08:22 EST
Article-I.D.: cbmvax.1371
Posted: Mon Feb  9 01:08:22 1987
Date-Received: Tue, 10-Feb-87 04:28:08 EST
References: <736@vaxb.calgary.UUCP> <1164@cbmvax.cbmvax.cbm.UUCP> <1986Dec24.185704.2125@utcs.uucp>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 39
Summary: long delayed answers

In article <1986Dec24.185704.2125@utcs.uucp> wagner@utcs.UUCP (Michael Wagner) writes:
>
>Actually, there are three DMA slots (hardware manual, pg. 187).  
>Why so many?  If I understand the disk section of the hardware manual, 
>each time slot transfers two bytes to/from DSKDAT(R) (pg. 235).
>Each slot should be good for 30K of data transfer (15K+ scans per second*2).
>The disk can only produce 28K/second of data (5 RPS*.5Ksectors*11sectors/rev).

Chances are the floppy controller was designed to cope with 8" floppy drives
or future double density 3.25" drives.  These would require at least double
the transfer rate of the current drives.

Designing things like this is a good way to avoid future embarrassments...

>Are the second and third DMA slot always unused?

The three slots correspond directly to three fifo stages in the controller
logic.  Since the fifo is initially empty, all three slots will get used on
the first fetch for a write, if nothing else.

>Can one disk seek while another transfers data?
>Can two transfer data at the same time?

Since the disks are effectivly daisy chained on single cable, it is not
a very good idea to have two drives selected at once, even though reading
and stepping are handled as separate functions.

>Can the blitting to decode a sector overlap with reading another track?

No reason why not, the floppy controller had priority on those three slots
when it wants them...

>In current practice (V1.2), does overlap occur?

I don't know.
-- 
George Robbins - now working for,	uucp: {ihnp4|seismo|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)