OT(?): Emulation XKCD

Charles Anthony charles.unix.pro at gmail.com
Wed Oct 30 17:50:06 CDT 2019

On Wed, Oct 30, 2019 at 2:50 PM Zane Healy <healyzh at avanthar.com> wrote:

> > On Oct 30, 2019, at 2:35 PM, Charles Anthony via cctalk <
> cctalk at classiccmp.org> wrote:
> >
> > For the dps8 emulator, I wrote (for expediency) the I/O code to complete
> > immediately. When the CPU executes an I/O instruction, the I/O is
> completed
> > and the interrupt posted before the next instruction is executed. As the
> > emulator was (at that point) single threaded, there was no performance
> > reason to do otherwise, and delaying interrupt delivery was additional
> code
> > that I didn't want to write and debug. The consensus in the Multics
> > community was that this was *probably* OK; the interrupt structure was
> > robust and the interrupt handling code well written, and should be able
> to
> > cope. But everytime a runtime failure occured, the question popped up: is
> > zero-latency I/O the issue?  I ended up adding code to delay interrupt
> > delivery as a run-time configuration option so that that possibility
> could
> > be checked.
> >
> > The XKCD is dead on for me. I have had that conversation.
> >
> > -- Charles
> If you’re on this list, does this mean this is a good place to ask Multics
> questions? :-)  Yes, I have a couple.
I would think that Multics is well inside the cctalk purview. There are
several Multics knowledgeable people lurking on this list, and if we can't
answer a question, we know people who can. Ask away...

-- Charles

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