Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!apple!oliveb!amiga!cbmvax!jesup
From: jesup@cbmvax.UUCP (Randell Jesup)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Ohhh, just another hack idea.
Keywords: Bigger floppy drive time
Message-ID: <6655@cbmvax.UUCP>
Date: 20 Apr 89 22:47:07 GMT
References: <10751@mcdphx.phx.mcd.mot.com> <89Apr19.165456edt.9318@ois.db.toronto.edu>
Reply-To: jesup@cbmvax.UUCP (Randell Jesup)
Distribution: na
Organization: Commodore Technology, West Chester, PA
Lines: 20

In article <89Apr19.165456edt.9318@ois.db.toronto.edu> fche@db.toronto.edu (Frank Eigler) writes:
>Another question, something in the same area.  Is it possible/has anyone
>ever written a trackdisk.device replacement that uses RLL format instead
>of MFM on a floppy?

	No.

>Or, is it possible with the hardware at all?

	Probably yes, though it may require better than normal media
(just as some ST506 drives can't handle RLL).  I suspect the hardware in
paula and the drives could do it, though I'm not certain.  The real killer
is encode/decode.  MFM decode is trivial (((word[i] & 0x55555555) << 1) |
(word[i+(BUFFSIZE/2)] & 0x55555555)) - I may have which word is shifted
wrong, check the RKM.  The blitter can do that in one pass, and store it in
the users buffer.  Decode is trickier, takes 4 passes, but the blitter can
still handle it.  RLL would be real tough with the blitter.

-- 
Randell Jesup, Commodore Engineering {uunet|rutgers|allegra}!cbmvax!jesup