Subject: Re: Floppy driver
To: Brad Pepers <>
From: Mike Schwartz <>
List: amiga-dev
Date: 02/28/1994 12:48:26
At 11:40 AM 2/28/94 -0700, Brad Pepers wrote:
><lots of stuff deleted>
>> > I was talking about a lower level than the filesystem. MSDOS disks are
>> > formatted in a different way and all the track/sector information is
>> > different. The low level disk reading code has to be changed first
>> > so that it can even find any data on MSDOS disks. Once that is working
>> > the msdos filesystem that comes with netbsd can be used.
>> Just as an aside - have you thought about looking at the PC0: driver
>> to see how Amiga resolved those differences?
>>  - Eric
>I think I know how to do it. There will be a bit or two in the minor #
>which tells the driver what type of disk it is. Then the code that does
>the track decoding can be different. What I'm not sure of though is if
>the MSDOS disk ca be handled in the same way as the amiga (on a track
>basis - not by sector).

No you can't treat an MS-DOS disk as you would an ADOS disk.  If my memory
serves correct - and forgive me if it doesn't - we're going back at least 3
years :-)  What I remember having to do was to turn on DMA on a sector by
sector basis.  And I think that the WD chip writes a magic MFM word (DSKSYN
byte) before each sector.  And I think that ADOS writes out even and odd
bits to separate memory chunks (after you read in a track) but the WD chip
does not -
hence your blitter MFM encode/decode are radically different.  I also remember
that I had to determine wheter the DMA to be started was indeed for the
sector I wanted.  It would obviously help to get a DOS formatted floppy and
examine it.

>+----------------------------Ren & Stimpy--------------------------------+
>| "Psst. Hey Guido. It's all so clear to me now. I'm the keeper of the   |
>| cheese. And you're the lemon merchant. Get it? And he knows it. That's |
>| why he's gonna kill us. So we gotta beat it. Yeah. Before he lets      |
>| loose the marmosets on us! Don't worry, little missy! I'll save you!"  |
>+------------------ Brad Pepers -- -------------------+