Date   : Sat, 04 Mar 2006 23:58:27 +0000
From   : Fragula <fragula@...>
Subject: Re: Warning: Sad case on list!

John Kortink wrote:

> There's close to no other hardware to emulate
> in a 2p. That's the beauty of it. Not even an interrupt in sight.
That's the beauty of the Tube system indeed. So easy to get a CPU
basically up, without having to write a load of device handlers just to
get a basic monitor together.

Have to question the interrupt bit though, Its a helluva long time ago,
and I really should really check the circuit diagram, but I'll live
dangerously on this one. Feel free to flame me if I'm wrong.

There are a couple of tricks the 2Ps code does.. First the stuff in the
host (DNFS or whatever) does its initial stuff, the 2P initialises, and
uploads (the 2p being the initiator) replacement interrupt handlers over
to the host, trapping IRQs and so I have read, NMIs too.

The priority of things is changed a bit in the host, as the Tube
interrupts have a very high priority indeed.

The host is /almost/ the only thing that can interrupt the 2p. (i.e. the
80186 has internal timers that interrupt, this needs to be suppressed
during certain host operations, I guess disc/net accesses and the like
where the host could "get ahead" of the 2p.

Its a pretty clever system really.

Cheers!

M.