28 Mar
2016
28 Mar
'16
4:44 p.m.
On 2016-03-28 16:18, Noel Chiappa wrote:
I don't think anything actually used SPL 7, as far as I can remember.
Right. A lost interrupt is a potential disaster and is never acceptable.
What we're talking about here is what happens after the interrupt.
I think I at least played around some with this on PDP-8 systems, and
seem to remember it working right there. But I have not done so on PDP-11s.
This is also a pretty important point. But one which also begs the
question how the splxxx() functions in Unix worked back then. Or did
Unix not use this pattern and these functions back when the 11/40 was
relevant?
My interest here is also very much on facts and technical points. I do
not want this to become some religious argument.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt(a)softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
From: Dave
Horsfall <dave(a)horsfall.org>
SPL 7 was only used by the clock interrupt
Err, according to the 1975 Peripherals Handbook, both are BR6. (Sorry, only
interested in accuracy.) Slightly
longer? I think it was Lions himself who used to teach us that
a lost interrupt is nasty :-(
The interrupt isn't lost, it's just that the OS does a WAIT when it should
perhaps return and start up some user process - but that resumption of doing
user computations is delayed by at most 1 clock tick (some other device may
interrupt during the WAIT, before the clock does). Anyone here
remember overlapped seeks on the RK-11 failing under Unix
I'd be interested in the details of this. The V6 RK driver didn't use them,
but the RK11-D does claim to support them (having spent a modest amount of
time looking at the drawings), so I'd very much like to know what the bug was.
I know that
Kevin Dawson (I think) tried it on my /40 as well
The 11/40 does not have the SPL instruction; see the '75-'76 PDP-11 Processor
Handbook, pg. 4-5. (Again, sorry, just want to be accurate.) Christ, but
this is starting to sound like some religion or other.
I am only interested in correct data.