Close

This is the tangent that doesn't end

A project log for Improbable AVR -> 8088 substitution for PC/XT

Probability this can work: 98%, working well: 50% A LOT of work, and utterly ridiculous.

eric-hertzEric Hertz 02/24/2017 at 06:070 Comments

yes it goes on and on, my friend.

Trying to backup an old/unique KayPro's system diskette... Yep, we're talking a 30y/o diskette.

Have managed, allegedly, to extract all but 60 or so of its 800 sectors. Though, now that I've combined the majority of the data I have extracted, I've discovered that my methods for combining that data was neglectful of some key information... On the plus-side, I don't think I need to add any wear to the diskette to fix that neglect. On the other hand, that combination of extracted-data, alone, was a good two days' worth of work that now has to be repeated in a new, more complicated, way which I can barely wrap my head around.

So far, we've got the KayPro's 360K floppy drive attached to a Pentium running linux, using fdrawcmd and countless hours of scripts reading and seeking and rereading and reseeking from the other direction... different delays for allowing the head to stop vibrating from a seek, different delays to make sure the spindle's reached the right speed...

Now I'm using the 1.2MB floppy drive to try again... one thought being that maybe the disk's spindle/centering-hole might've worn over time, in which case the actual tracks may be wobbling with-respect-to the read-head. So, if I use the 1.2MB drive on those tracks, I'll not only have skinnier read-heads that're more-likely to stay "on-track", I'll also have *two* to try. Also, I imagine the head-amplifier expects a weaker signal, so probably has better SNR, etc... Seems like it could be helpful. But I initially found that the 1.2MB drive wasn't reading valid data from the sectors nearly as often as the original 360K drive the system (still, 30 years later) boots from, so switched over to that one early-on.

Dozens of extraction-attempts... Some of those runs had the head seeking back and forth for hours on end. Noisy Bugger. But I only stopped when a few runs in a row weren't able to extract more of the missing data... So, each of the *countless* attempts before that managed to recover more missing data... So that's cool.

It's a wonder these things ever worked, really... There're so many factors! I'm betting even minor amounts of thermal expansion/contraction could have a dramatic effect on head-alignment.


But I haven't really been able to think about anything else since this stupid side-project started... kinda draining, to say the least. Especially considering I don't know if I've really got a use for it. Coulda been using that time to work on #sdramThingZero - 133MS/s 32-bit Logic Analyzer instead, which would render this ol' clunker a bit obsolete... but my head's just not been there.

It is cool, though... 20MS/s from the 1980's! The entirety of the software fits on a 360K disk, and still manages to do things like advanced-triggering and disassembly of the waveforms (in Z80, anyhow). Would definitely be a shame to see it lost to bit-rot.

Discussions