Date   : Wed, 27 Jul 2005 11:23:38 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: ARM copros, speech cartridges, real timeclocks, etc

On Tue, 2005-07-26 at 21:57 +0000, Jules Richardson wrote:
> You know, for some reason I think that the ACW (and possibly the ABC3xx
> machines) perhaps did make use of an interrupt mechanism. I just can't
> remember who told me that and exactly what I was told now though! I've
> got the ACW schematics; I'll have to have a look and see. Maybe it
> wasn't through the Tube though and wired in via some other way...  (of
> course the BBC I/O processor side ran BOS, so it's entirely possible the
> Tube-handling code was entirely different to a normal BBC)

Hmm, found the ACW service manual. It says the following TUBE lines are
used:

  8x data, A0-A4, R/NW, 2E, NRS, and NIRQ.

It says that an interrupt scheme is used on the copro side of the Tube
and polling on the I/O processor (bbc B+) side of the Tube. That sounds
normal; I assume a copro can interrupt the I/O processor to do stuff,
it's just that the I/O processor can't interrupt the copro (it's polled
only)

But then further on it says of the copro that "the only source of
interrupts is the Tube", implying that the B+ board *can* interrupt the
copro. Hence I'm confused :)

cheers

Jules