RFC: Floppy reader/writer project (recovering UniPlus Unix for the Lisa)

[Ray Arachelian]

Philip Pemberton wrote:
> The problem is, you'd have to modify the drive to do that. The read 
> head amplifier on just about all floppy drives (certainly all modern 
> drives) does some pulse-shaping on the signal as well.
>
> What you'd have to do is find the amplified signal, then bring it into 
> the range an A/D controller would accept, and digitise it. You'll 
> probably want at least 20 megasamples/second to get a good amount of 
> resolution out of the data, and for a revolution time of a second, 
> you're talking 20 megabytes of data per track (assuming you use an 
> 8-bit converter).
>
Sounds like it might be a very useful thing to build.   (I don't even 
have my hands on the disks at this point, he's resorting to using 
CopyIIMac right now, which hopefully will be able to read a bit past the 
errors.)

So such a setup would need a dedicated machine... at 20MB/track it would 
need something like 3.2GB for a whole floppy, maybe double that if we 
wanted to include half-tracks and extra tracks, and whatever custom 
software to try and clean up the signal.  Sounds like a machine with a 
DSP would help speed up the post processing too.  Ouch...  Would still 
be worthwhile assuming that the media itself hasn't been physically worn 
off and just degraded...  I guess something like this is what the data 
recovery guys use...

> What you can do with the pulse-timed data is read it out, then look at 
> it and analyse it based on the encoding rules. So you could throw away 
> data pulses that are obviously too close to others, or adjust the 
> timing window dynamically to compensate for motor speed variations.
>
> One of the ideas I had for the Ext I/O inputs was a motor 
> tachometer/position detector that constantly tracks the instantaneous 
> speed or position of the motor spindle. Then you can look at the data 
> from that, and adjust the timing values to get rid of motor speed 
> induced errors. After that, all you're left with is the comparatively 
> small error from the clock source (usually the crystal). This sort of 
> thing probably wouldn't be too hard to add to the average 3.5" or 
> 5.25" disc drive... the hard part would be getting the encoder wheel 
> exactly centred on the spindle hub.
>
I suppose you could also slow down the motor speed, as to increase 
resolution, but all of these would be pretty invasive drive mods.   
(you'd still need some way to precisely measure the distance traveled by 
the motor.)

I'm hoping he can get some data off these disks.  It's a bit more 
complicated, there's an ebay auction involved too.  He's promised to at 
least try to convince the buyer to let us recover the data off these 
disks, so  we may have access to these for a while after the auction 
ends.  If not, I'm afraid this OS will be lost depending on the buyer's 
luck/willingness to share... :-(

Any chance someone else on this list has a copy of UniPlus Unix?