6 Sep
2006
6 Sep
'06
6:59 a.m.
I have a PDP-8/A with an RL-01 drive which does not want to boot and am
looking for advice ...
The machine (outlined at
http://www.technology.niagarac.on.ca/staff/mcsele/pdp8a.html) is
functioning properly but 'hangs' when the bootstrap is exectured for the
RL-01 drive (the FAULT light blinking briefly then extinguishing). The
RL-01 disks were last booted about 10 years ago and were supposedly
bootable then (presumably with OS/8).
Stepping-through the bootsrtap code, the program hands on the READ
HEADER function. A diagnostic program was written to do a READ ERROR at
that point and apparently a DCRC error is occurring (AC=4401 in response
to the RRER instruction). A GET STATUS was also run and the drive
operation verified, but apparently there is still a CRC error.
I have outlined all tests perfromed on that web page above (including
status words in the silo after the GET STATUS command).
If anyone has experience with such a drive I'd love to hear your
thoughts on it! I have tried two supposedly bootable cartridges and
received the same results.
Thanks ... Mark
Professor Mark Csele
Niagara College, Canada
300 Woodlawn Rd., L-8
Welland, ON, L3C 7L3
(905) 735-2211 x.7629
E-Mail: mcsele at niagarac.on.ca
URL: http://technology.niagarac.on.ca/people/mcsele
Author of "Fundamentals of Light Sources and Lasers", Wiley, 2004
6 Sep
6 Sep
5:06 p.m.
On 9/7/06, Mark Csele <mcsele at niagarac.on.ca> wrote:
I have a PDP-8/A with an RL-01 drive which does not
want to boot and am
looking for advice ...
http://www.technology.niagarac.on.ca/staff/mcsele/pdp8a.html) is
functioning properly but 'hangs' when the bootstrap is exectured for the
RL-01 drive (the FAULT light blinking briefly then extinguishing). The
RL-01 disks were last booted about 10 years ago and were supposedly
bootable then (presumably with OS/8).
You didn't say anything in your message or on your web page about
the READY light. Is it lit when you mount the pack? If it's lit, does it
blink when you step through the bootstrap?
It's a really fundamental thing, but since it seems that you recently
acquired the system, did you lock the heads before transporting it?
(small metal square with one screw on the corner that blocks the
heads from sliding out during transport) If someone else locked them,
did you _unlock_ them? If you moved the drive with the heads
unlocked, that could be your problem. If there was a pack in the
drive at the time, that _really_ could be your problem.
Something else to check is the cable. I have a PDP-8/a w/RL8A.
I recall that the controller-end of the cable is somewhat fragile
(for those that don't have one to look at, it's not like an RL11;
it's a bare Berg connector with 40-ish wires coming out of a round
RL cable in a twisted fan - more like the cables I've seen for an
RLV12). I know on at least one occasion, I had to repair one of
the outer conductors of my RL8A cable because the wire popped
out of the crimp-on pin in the Berg connector.
As for your speculation on disk capacity, the RL01 is a 5MB unit,
under OS/8, it presents three "devices" - an RL0A of 2MB, an
RL0B of 2MB, and an RL0C with the remaining 1MB.
Due to how it assigns the blocks, RL0A and RL0B are laid out
somewhat efficiently; RL0C is the "leftovers", and when you use
it, the disk seeks all over the place. It's not uncommon to use
RL0C as an archival area and to not necessarily even load the
drivers for it - freeing up a driver slot for, say, a floppy or other
storage device.
-ethan
7 Sep
7 Sep
2:50 p.m.
http://www.technology.niagarac.on.ca/staff/mcsele/pdp8a.html) is
functioning properly but 'hangs' when the bootstrap is exectured for the
RL-01 drive (the FAULT light blinking briefly then extinguishing). The
RL-01 disks were last booted about 10 years ago and were supposedly
bootable then (presumably with OS/8).
You didn't say anything in your message or on your web page about
the READY light. Is it lit when you mount the pack? If it's lit, does it
blink when you step through the bootstrap?
It's a really fundamental thing, but since it seems that you recently
acquired the system, did you lock the heads before transporting it?
(small metal square with one screw on the corner that blocks the
heads from sliding out during transport) If someone else locked them,
did you _unlock_ them? If you moved the drive with the heads
unlocked, that could be your problem. If there was a pack in the
drive at the time, that _really_ could be your problem.
My experience of RL01's and RL02's suggests that there is considerable
friction in the positioner mechanism (unlike, say, an RK05), so it's not
_essential_ to lock the positioner for transport. On the other hand, it
does no harm to do so, and might save the heads.
Something else to check is the cable. I have a PDP-8/a w/RL8A.
I recall that the controller-end of the cable is somewhat fragile
(for those that don't have one to look at, it's not like an RL11;
it's a bare Berg connector with 40-ish wires coming out of a round
RL cable in a twisted fan - more like the cables I've seen for an
RLV12). I know on at least one occasion, I had to repair one of
the outer conductors of my RL8A cable because the wire popped
out of the crimp-on pin in the Berg connector.
I beleive all the cables are electrically identical. Certainly the RL8
type of thing is used on an ELV11 in the MINC system. The main reason
there are different cables is the physical problem of getting the cable
round the inside of the system box -- with osme machines it's easier to
use a ribbon cable, with others it's easier to use a cylindrical cable.
Anothre thought is that there's a PLL circuit in the controller used as
part of the data separator (or at least there is in the RL11 and RLV11
controllers). Maybe something in that has drifted over the years, and
it's no longer locking. Or maybe some chip has just failed.
How I'd handle this (given my hardware background) is to remove the
access cover on the drive, put a (scratch) pack in and spin up. Check the
ready light comes on and the heads load.
Then write little programs on the PDP8 to read out the status registers
etc. See if you can read the drive status, and see if it's reasonable.
Try moving the heads to different cylinders (and actually watch the
positioner to make sure it's doing the right things). Then try reading a
sector. If you get an error, work out exactly what the error bits are
telling you. TRen dive in with the 'scope and logic analyser to see what
is settign those erorr bits, and work backwards until you find out why.
-tony
6681
days inactive
6682
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ard＠p850ug1.demon.co.uk -
ethan.dicks＠gmail.com -
mcsele＠niagarac.on.ca