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The "MFM" decoder can handle FM, MFM, MMFM, GCR, and could be extended
to support RLL. I have only tested with FM and MFM. These are all
related encodings but "MFM" is the most distinctive name so it is
being used to describe the family. The family of encodings was used in
magnetic tape storage, but the focus here is floppies with a side of
hard drives.
The MFM decoder is pretty simple, and doesn't attempt to separate
clock/data or align bytes. The method of doing so varies per sector
format so that responsibility is left to the consumer, which makes
configuration for the user easier. The decoder also doesn't try to act
as a PLL. Someone else can enhance it, but it currently seems to work
fine even on some early-1980s floppy disks/drives.
The Floppy decoder can also be used with ST506-style hard drives...
which are not floppies. But the encoding was very similar when MFM was
in use. I have not tested an ST506 using IBM-compatible MFM formatting,
but I have tested a Micropolis-encoded HDD which is a slight variation
of the MFM FDD format.
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