19 Aug
2006
19 Aug
'06
5:05 p.m.
Tony Duell wrote:
I am not sure how much of the disk structure you can
directly get from
the POS system calls. For example, there are 4 words of filesystem
pointers in the sector _header_, that's why the DMA controller is
somewhat complicated (it can be set up to transfer those pointers to one
buffer and the sector data to another part of memory altogether). My
guess is you can't directly get those header words using POS calls.
It may not matter. From what I rmemberm the infromation is stored
elsewhere too (probably in the file descriptor blocks). THe pointers in
the headers are used for speed and to help recover the filesystem in the
event of disk problems.
Yes, I was wondering about this as well. The POS
documentation mentions
this header information as being present on disk but doesn't describe it
in detail. The UnitIO "DiagRead" command returns an 8-word block of
header data on a block read -- I don't know if this has any relationship
with the physical bits on the disk; but just in case I made sure to copy
those along with the 256 words of actual sector data.
At any rate, the header data doesn't appear to be necessary for parsing
the directory structure; I've written another quick and dirty utility
(on the PC this time) to read in the disk image and dump the directory
structure and files to disk without too many hairy issues. (The utility
and all the files on the disk are now on my website at
http://yahozna.dhs.org/computers/software/PERQ).
Nothing too incredibly exciting on the disk, but it's nice to have it
archived for posterity.
Do you have the POS source code? I thin I hace most of
the Pascal (not
microcode, though) sources for one version.
I do not -- what I have on the PERQ is the bare minimum necessary to
compile and link pascal programs.
Which drive do you have? The 14" SA4000 unit used
in the 1 and 1a seems
to suffer from drive belt trouble and little else. The 8" Micropolis 1203
used in the 2T1 has problems with the servo analogue electronics -- I've
had to replace op-amps and the power amplifier chip in those. The 5.25"
units used in the 2T2 and 2T4 suffer from the same problems as PC hard
drives of the time, because that's what they are :-)
I have the 14" SA4000 drive. The belt had a problem where it'd
immediately slip off at power-on. It wasn't loose at all, but the
inside of the belt was worn smooth. For the time being, I've turned the
belt inside out and I haven't had any problems since.
One quick question: Any ideas what digitizer pucks are compatible with
the BitPadOne? My PERQ came with a very very crude home-made puck
(http://yahozna.dhs.org/computers/perq/photos/digitizer-small.JPG). It
just barely works (the cursor jumps all over) and it's falling apart.
I'd love to replace this with something more authentic. Or at least
something that works correctly.
Now to start hacking away at that emulator... :)
Thanks again,
Josh
