18 Dec
2005
18 Dec
'05
11:49 p.m.
BTW, belated thanks for your answers to my questions
about ImageDisk
on my previous go-round with it on HP150 stiffies.
I haven't had time to poke at ImageDisk again, but the answer I took
to heart was that the implementation of the PC floppy-disk system is
sufficiently variable that reading HP150 stiffies isn't reliable
AFAIK all HP150 disks are double-density. Certainly the schematics for
the 9114 imply that unit can _only_ operate in double density mode, and I
think the same is true for the HPIB-interfaced drive units.
That makes life a little easier for you, since all PC disk controllers
can handle that.
The big problem with HP disk units is that there was some intellegence in
the drive units (IIRC a 68x09 processor) and they did things like bad
track replacement _trnasparently to the user_. If a double-sided disk is
'perfect' (no bad tracks), then phgysical cylinders 0-76 are used for
user data, 77 and 78 are unformatted, and 79 contains something that
indicates there are no track replacements, the usage counter, etc. From
what I can see, this was never documented in any HP manual.
When I wrote programs to read 9114 disks on a PC, I have to admit I
ignored this, and just imaged cylinders 0 to 76. When dumping back, I
assumed a perfect disk that had been formated on the HP drive, and just
wrote cylinders 0 to 76. Amazingly nobody seems to have had problems from
this.
As an aside, it had crossed my mind to use the
Portable Plus and
9114B to build ImageDisk-format image files, but looking at the
Portable Plus Technical Reference, there's no well-documented way
to read sectors from an HP-IL-attached disk. Bummer!
I am not sure how general the 9114 can be -- I've only ever used it to
produce disks with 16 256-byte sectors per track. And to do that you can
use a command set called 'Modified Filbert Protocol'. This is a superset
of the commands to the 82161 tape drive (codenamed Filbert, of course),
which are documented in the manual for that product. The best way to find
out the extensions is to read the HP71 HPIL IDS volumes, and the HP75C ROM
source and comentary. I spent many a long night doing just that...
From what I rmember of the Portable Plus, you can take
over the HPIL
system and sent arbitrarly DDT and DDL commands (which is what you
need
to do). Just don;t do it on any disk you expect to be using from MS-DOS...
If you think you might find useful stuff in my 9114 disk reading
programs, feel free to take a look, They're on hpcc.org somewhere,
they're GPLed C sources. If you can't find them, I'll mail you a tar
archive or something.
-tony