dfitoimd: decoding Intel M2FM floppy flux images (was Re: Intel 432 floppy flux images for decoding)

[Eric Smith]

On Mon, Aug 8, 2016 at 12:17 PM, Chuck Guzis <cclist at sydex.com> wrote:
> I did my cw-MMFM converter in 32-bit C years ago, but then I use my own
> format for the cw files (i.e. I don't use cwtools), so it's probably not
> a lot of use to folks--but it's fast.  Metadata is important to me and I
> pack my cw image files with as much as possible.

If you're willing to share the code, I'd be interested in taking a look.

> I record two revolutions worth of data per track to get *everything* and
> also to give an implied second chance at data that the first rev may
> have missed.

The dfi images I'm working with have two revolutions. One limitation
(bug?) in my current data separator code is that the "VCO" of my ADPLL
always starts at the nominal frequency when the code starts processing
a track, rather than the frequency it settled to on the previous
track.  I should change that on the assumption that the rotation rate
is generally going to be the same for all tracks.  Anyhow, right now
the code processes both rotations (or as many as are represented in
the dfi image), but with only a single pass, so sometimes it doesn't
successfully decode a sector in the first revolution, but gets it in
the second.  I should change the code so that if there's only one
revolution in the file, it cycles through it twice (or a configurable
number), to give the ADPLL a chance to settle.

> To date, on Intel and AES MMFM (they're different) disks, I'm batting 100%.

Is there any documentation about AES MMFM format online?

So far I haven't encountered any two M2FM/MMFM formats that are the same.

> P.S.   On my bucket list, I'm curious if anyone's ever worked out the
> internals of the WD9914 data separator chip.

Typo in the part number?  The WD9914 is WD's second source (or clone?)
of the TMS9914 GPIB chip.

I was able to find some info on the internals of the SMC FD9216 data
separator. WD second-sourced that as the WD9216.