21 Oct
2004
21 Oct
'04
3:13 p.m.
Jim Donoghue wrote:
I have some 5 1/4" hard-sectored disks that
contain CPU microcode. They
aren't 'formatted' with a filesystem, but are read with a simple board
that contains some 9602's, a shift register, and a Z80. A dilemma:
should I try to intercept the data from the board, write it to flash
memory, and build a board to replace the whole Z80/hard-sectored disk
thing, *or* try to build something to write the data stream out to
another 5 1/4" disk. The Z80 doesn't care about the sector pulses - only
the index pulse. So I could get away with a standard floppy instead of a
hard-sectored one.
The disk thing would allow me to keep using the original hardware, which
would be nice, but I don't know the first thing about attempting to
write the data stream back to the disk.
I have no backups of the microcode disk, and no way to replace it when
it dies. Every time I fire the thing up I feel I'm getting a little
closer to it's death...
Jim, if you want to build hardware, you can, but personally, it would be
easiest to use a catweasel card -- they can read and write disks. The
next generation catweasel card is supposed to be better at handling hard
sectored disks, but since you said the hard sectoring doesn't matter,
any catweasel card should do.
It simply counts how many ticks of a 14 MHz (or other selectable
frequency) clock occur between each flux transition and logs it into a
RAM. You simply would have to write a bit of software to step the head
to the right track, capture a snapshot of one revolution, save the data,
step to the next track etc. Then, put in a fresh disk and hand the
catweasel card the flux reversal timing that was recorded and ask the
card to write out a bit pattern matching the timings you've just given
it. If you have two disk drives connect to it, you can ping-pong
between then and do the copy that way.
So you can make a clone of the disk without having to reverse engineer
the disk encoding or format at all.
For the $90 or so that it costs, it has to be cheaper than your time to
build something custom.