25 Sep
2014
25 Sep
'14
3:31 p.m.
On 2014-Sep-25, at 2:28 PM, Paul Koning wrote:
On Sep 25, 2014, at 4:40 PM, Brent Hilpert <hilpert
at cs.ubc.ca> wrote:
Although, if by restore machinery you mean the state-machine/sequencing-logic that does
the (re)-write, it can still be more subtle than that.
In my case it was just one bad address-wire driver transistor, such that the failure was
for only one direction of current flow - the 'write' or 'set' direction.
It failed as you suggest - could read once but failed to rewrite - but did not affect the
entire core array, just a sub-set of 64-word blocks.
On 2014-Sep-25, at 11:43 AM, Paul Koning wrote:
That?s a good point. If the restore machinery is not working, you can only read once,
after that you?ll see zeroes. A quick check would be to pick some location and read it
several times. If that works, the restore logic is at least somewhat functional. On Sep 25, 2014, at 2:33 PM, Simon Claessen
<simski at dds.nl> wrote:
I can only encourage the latter approach, I did something similar for my HP 2116C 10
years ago when I received it. Once I had a monitor written and loaded I was able to
recover the remaining contents of core. It was enough to show the last thing the machine
had been doing was running a BASIC game, apparently in July of 1983.
http://www.cs.ubc.ca/~hilpert/e/HP21xx/HP2116CSys/index.html#recovery
Due to a hardware fault in the core memory, I (had) had only one opportunity to get a
full dump, which I had missed due to checking memory from the front panel and not knowing
about the fault, so I didn't get the entire contents. In my case hindsight is great,
but it's something to keep in mind if recovering the contents is of some concern.
The pdp8/f we got last week is working now, after
forming the capacitors on the lineair powersupply and testing it with dummyloads. there is
a 8kword and a 16kword corepack in the machine. we would like to dump the contents of the
core to serial to preserve the original contents for later examination while we can to
tests with the machine.
is there a way to do this, using a empty part of memory and a M8650 uart?
One way would be to wiggle the console switches under program control, as the CHM PDP-1
team did according to an article from a few years ago.
Another would be to find, or write, a simple memory dump program, and load that in a
small bit of memory that you have previously saved by hand (from the console
switches/lights). I don?t speak PDP-8 assembler, but I imagine such a program wouldn?t be
more than 30-50 instructions total. Still, safest would be to hook to the console. A
BeagleBone Black has enough I/O lines to do that, I think, so it sounds like just some
level shifters and a modest amount of software.
paul