Open-source floppy reader: the data separator/sync-er works!

Ethan Dicks ethan.dicks at gmail.com
Tue Apr 10 12:28:42 CDT 2007


On 4/10/07, Chuck Guzis <cclist at sydex.com> wrote:
> On 10 Apr 2007 at 3:24, Jules Richardson wrote:
>
> > I suspect it's just to read disks that don't start the track at the index
> > pulse (I'd wondered the same thing until his post about Amiga floppies).
>
> The buffer on the CW is large enough to record much more than a
> single revolution of a diskette, so when dealing with diskettes of
> this type, I fill it up with larger sample.   Decoding then proceeds
> with the first good (complete) sector in the buffer.

That's how the Amiga trackdisk.device does it... turn on the motor,
slurp up a few thousand bits, then go looking for the first header.
It does help that there's a set of blitter terms to convert MFM to
binary and back using spare cycles from the graphics co-processor.

> I don't even
> bother to pay attention to the index pulse in this case--I just allow
> a certain amount of settling time after seeking and begin recording
> for a sufficiently long time to grab about a rev and a half.

I can
t quote chapter and verse for the exact amount of excess rotation that
trackdisk.device does, but anecdotally, I recall 1.1 revolutions.

-ethan



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