12 Jan
2011
12 Jan
'11
12:35 p.m.
Unusual vectors. BTW, if you ever need to find out
what vector
something is using, and can make it interrupt, you can set up a "trap
catcher". This is also used to identify what device is causing
interrupts or traps if you're getting rogue ones. Basically you fill
the vector space (or floating vector space) with pairs of words, where
the first word for each vector is the address of the next word, and the
next word contains a zero. This has the effect that, when the CPU uses
I seem to rememebnr that RT11 (and possible other OSes) does this to some
vector locations anyeay. I recall srotign out a PDP11/34 that was failing
with some kind fo illegal address (or illegal instruction, something like
that) trap when it tried to boot RT11. The machine would halt with the
address of the illegal whatever trap in the display
The apporpirate vector locaiton did, indeed cotnain .+2, 0 . And a bit of
work showed it was indeed trapping to that location, and not (say)
jumping to the second word for some reason. After much testing, etc. I
finally found the proble, A dodgy swithc on the DL11-W card was truning
the console interrupt vecotr into the illegal instruction one. So as soon
as the system eneabled interrupys on the console port and the console
port interrupted (probably to say it was ready to outptu a character),
the system halted.
-tony