8 Dec
2008
8 Dec
'08
3:03 p.m.
Jules Richardson wrote:
Mmm, there's just a bit of a difference between "what the math says" and
"what
Murphy allows".
I still harbour a hatred for ST506 drives. Although mainly directed at the
Kalok 20MB piles-o'-crap.
I actually got banned from the school computer lab many years ago for
allegedly destroying the hard drive in an Acorn A440. Said drive being a 20MB
Kalok thing that was shaky at the best of times. I was dragged out of class
for half a day to help the "IT expert" (actually Just Another Teacher [tm])
fix it. Most of that time was spent staring at !HForm's soak-test screen and
writing down all the errors, on IT Expert's orders. One every two sectors IIRC.
"Make sure you don't get ANY of the numbers wrong! You have to re-enter them
when it actually formats the drive!"
It's "find a clean-room" territory. The head preamps are usually mounted
near
the heads, often on the actuator arms themselves.
On floppy drives, you get a screwdriver and a soldering iron. Suppose you
could make a replacement logic board if you liked, but that's too much like
hard work IMO :)
Two chinchillas here (soon to be three). It's all fun and games until one of
them tries to get under the sink and ends up getting soaked...
Oh, food. A handful of pellets, a handful of fresh hay and a fresh bottle of
water every 24 hours. Not hard, just expensive :)
The problem with PCI is licensing -- you need a PCI Vendor ID, which you get
by joining PCI-SIG, signing the patent licenses and so forth. The damage? ?4k
per year last time I checked.
Or you move to China, open a factory and pick a number at random and pray it
doesn't clash with someone else's ID. Or pick one that isn't on the Linux PCI
Vendor ID list...
USB is open-licensed -- AIUI, it's a case of "do what you like as long as you
buy a Vendor ID and don't use the USB logo". The VIDs were $2000 last time I
checked, but a lot of IC manufacturers will sub-licence individual PIDs in
their VID block to their customers.
Or you ignore the USB-IF and pick a nice, random number that isn't on the
Linux USB VID list.
Yep. But I'm not sure that it's really rocket
science - assuming that
you know what encoding format the data's actually in, which is probably
the more difficult part. Coping with errors might be interesting in some
cases.
It isn't. The hardest part is converting from timing data back to an MFM
bitstream or binary data. You need to either handle changes in drive speed in
real time (i.e. track the read speed and continually adjust the 1t, 1.5t and
2t timing values) or do something similar to disk2fdi -- preprocess the data
and figure out a set of thresholds that work, assuming the disc is in good shape.
I wouldn't
expect it to be that fast, but ~15 minutes is probably a
reasonable estimate.
Well that'd do, I guess. Heck, that's hardly enough time for the
electronics to get up to working temp :-) But yeah, in the order of 15
mins is probably realistic - I think it normally used to take about that
to 'clone' a drive. Hmm, well you could potentially use several SRAM ICs
and couple them to
different buses as/when needed, but at the end of the day perhaps it's
just not worth the complexity.
The added board space is a bigger concern...
Thing is, the
AGC on the head amplifier will probably start boosting
the gain if it doesn't see any transitions in, say, 1/32 of a
revolution. If that happens, then you'll get a nice stream of garbage
(more likely spurious transitions inserted than transitions missed).
Hmm, true. I suppose anything's possible though, without knowing the
internals of every STxxx drive ever made :-) The only way I
can think of to get around that would be to remove the
head-amp and bolt on an analogue amplifier
I'm not sure how easy it is to tap into that kind of thing on a lot of
drives, though. Possibly best left for real emergencies on a
case-by-case basis... "It
slices, it dices, it makes coffee, it feeds the cat!* (* Subject
to software availability)" :)
We have four cats here, and they eat a phenomenal amount - I'm not sure
that your device could keep up. :-) That's
probably worth looking into, but I know very little about PCI
device design...
Ditto. Back in the day I wanted to get away from the internal card
approach - but these days it's possible to get a tiny, cheap motherboard
and should be relatively easy to build a networkable "external device"
that's a complete compact PC in its own right. I think I've got some Tandon and Epson drive
schematics kicking around
and they used separate stages. But tapping into the head signal on a
floppy drive is a darn sight easier than a hard disk...
Mainly because the manuals for floppy drives tend to include schematics... The
ST412/506 OEM manual doesn't.
Woooooo, black magic inside!
Yeah, I got around to thinking about moving the motors
elsewhere - but
you're right about the head gap. I suspect it just plain won't work, but
speculation's always interesting :-)
Many a good idea has been born of idle speculation and what-ifs.
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/