Date   : Wed, 27 Oct 2010 21:55:31 +0100
From   : jgh@... (J.G.Harston)
Subject: Reversing the Tube ULA (destructively)

Michael Firth wrote:
> needed for some specific re-implementations (e.g. the DMA functions used
> on the 80186 Co-Pro)

The 80186 doesn't use the DMA functions. The NMI from the Tube is
connected to the *80186's* DMA input pin instead of the 80186's NMI
pin. Transfers are still done as Tube NMI interupts, it's just that
the 80186 sees the Tube NMI interupt as a DMA interupt.

> implementation. This category is hard to be definitive about, but I
> think it includes the ULA "soft reset" and the "parasite reset" bits in

I've used the Reset function, and some SJ network utility tools also
use it.

> implementations. I think the "Host IRQ" feature and control logic is in
> this class, as the pin is not (by default) connected to the host on all

For years I've toyed with writing something that uses the Host IRQ signal
to do some sort of parallel processing, but have never got around to
doing it.

-- 
J.G.Harston - jgh@...