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Talk about flippy disks.

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David Given
2019-03-07 23:20:54 +01:00
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@@ -38,14 +38,57 @@ have either the adapter, the drive, or any 8" disks. If anyone wants to give
it a try, please [tell me about it a try, please [tell me about
it](https://github.com/davidgiven/fluxengine/issues/new). it](https://github.com/davidgiven/fluxengine/issues/new).
**Q.** Is this like KryoFlux / Catweasel / DiskFerret? Do you support KryoFlux stream files? **Q.** Does it work on hard sectored disks?
**A.** Probably? I already have decoder support for some hard-sectored disk
formats, based on Kryoflux streams people sent me, and the firmware supports
reporting index hole information, so in theory it _should_ work; but I
haven't had the chance to try it end-for-end. I really need a hard-sectored
5.25" floppy to test with.
**Q.** Does it work with flippy disks?
Uhhh... probably not.
So the problem with flippy disks (5.25" single-sided disks which could be
inserted upside down to read the second side) is the index hole. Trouble is,
the window to let the sensor see the index hole isn't symmetrical on a 5.25"
disk, so if you turn the disk upside down, the drive can't see the hole any
more:
<div style="text-align: center">
<a href="https://commons.wikimedia.org/wiki/Category:5¼-inch_floppy_disks#/media/File:Atari_Master_Diskette_3_DOS_3_Floppy_Disk.jpg"><img src="525-floppy.jpg" style="min-width:80%" alt="non-flippy 5.25 inch disk"></a>
</div>
Some flippy disks had two windows, so they'd work properly either way up, but
most didn't. This was fine on a lot of old machines because those drives
didn't have an index hole sensor. But a lot of modern drives use the index
hole to detect whether the disk is actually present and if they don't see it,
they simply won't work. There's nothing FluxEngine can do; it's a hardware
limitation.
(If you have one of the rare disks with two index holes, then FluxEngine
_will_ read those.)
There are workarounds. One is to read the data on the other side of the disk
using the other head --- because, of course, modern drives are double-sided.
Sure, the disk is spinning in the wrong direction, but that's no problem.
Except there _is_ a problem, which is the tracks on the two sides of the disk
are not in the same place; one side has them offset eight tracks compared to
the other. But a flippy disk has both sets of tracks in the same place,
because they're both accessed using the side 0 head...
The only real way round this is to modify a 5.25" drive. That's _seriously_
not in FluxEngine's remit. Sorry.
**Q.** Is this like KryoFlux / Catweasel / DiskFerret? Do you support KryoFlux
stream files?
**A.** It's very like all of these; the idea's old, and lots of people have **A.** It's very like all of these; the idea's old, and lots of people have
*tried it (you can get away with any sufficiently fast microcontroller and tried it (you can get away with any sufficiently fast microcontroller and
*enough RAM). FluxEngine can enough RAM). FluxEngine can read from KryoFlux stream files natively, and
read from KryoFlux stream files natively, and there's a tool which will let there's a tool which will let you convert at least one kind of Catweasel file
you convert at least one kind of Catweasel file to FluxEngine's native flux to FluxEngine's native flux file format.
file format.
**Q.** Can I use this to make exact copies of disks? **Q.** Can I use this to make exact copies of disks?