12 Jan
2015
12 Jan
'15
9:38 p.m.
On 2015-01-12 22:34, Vincent Slyngstad wrote:
Yep.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
From: Johnny Billquist: Monday, January 12, 2015 12:38
PM
Every interrupt, even if not nested, needs to save the AC, link, and a
bunch of other stuff.
But yes, if you centralize that part, then it also needs to be stashed
away before you allow another interrupt. It's two more words.
Of course I've done it. I suspect there is
not much I have not done on
a PDP-8. I've written programs on PDP-8 systems for over 30 years by
now...
No, you do not need a push/pop to have interrupts enabled while in an
interrupt handler on a PDP-8. As long as you know the same interrupt
will not trigger, all you need to do is store the return address from
0 somewhere else before ION, and then write it back to 0 after IOFF.
Well, and the AC and flags and any other context that the ISR needs.
Essentially, a "one deep stack" for the context, which is much easier
to implement. Like I said,
with the provisions that you do not reuse the same
functions from different interrupt handlers, and you know that the
same device don't interrupt again.
Yep. Generally, you can't share any storage between the various
routines while the interrupts are on, and you have to also prevent
re-entry of the routines you are already in.