Date   : Sat, 11 Mar 2006 22:39:41 -0000
From   : "David Harper" <dl.harper@...>
Subject: Re: Warning: Sad case on list!

Fragula wrote:

> I happened again across the technical description of the tube interrupt
> ops at
> http://www.nvg.ntnu.no/bbc/doc/Master%20512%20Technical%20Guide/m512tech04.htm
>
>
> <winces@... of link>
>
> But it seems to make sense (Not that I can remember where NMIVEC is or
> anything) because ths host coulnd't run in a tight loop when its busy.
> Drawing, getting FDC or ADLC interrupts.
>
> Hmm. AFAICS there is no cast-in-stone reason the parasite could not
> spinpoll during disk/net ops though, or for other reasons, poll on its
> internal interrupt for events.

Much as I respect Robin, he didn't get things quite right in his description 
of the 80186's Tube operation.

The 80186 co-pro is wired unusually. It doesn't use parasite NMIs for data 
transfer at all. The line that would be connected to the NMI pin for other 
processors actually is connected to control one of the DMAs integral in the 
80186. The NMI has quite a different function.

I will put some info about this on the web in a day or so.

David Harper