[Open-graphics] Video interrupt enable/disable

[Hamie]

On Friday 20 April 2007 13:09, mykrowatt at comcast.net wrote:
>  -------------- Original message ----------------------
> From: Dieter <netbsd at sopwith.solgatos.com>
>
> > So yeah, they used to make machines designed to run Unix.  People stopped
> > buying them, so they stopped making them for the most part.  Even Apple
> > stopped thinking different and now uses pee-cee hardware.  I guess Sun
> > probably still makes sparcstations, anybody else?
>
> A lot of military and industrial real-time machines are based on VME bus. 
> It never got huge, but it never went away either.  It uses a vectored
> interrupt system with 7 priority levels.  It has neat multiprocessing

I think (Someone correct me if I'm wrong here) this was because it was mostly 
based around the 68000 processor... Early Sun Servers with 68k processors in 
them were VMEBus. Some later Sun 4 servers (Sparc based) were also VME bus. 
(Sun 4/330 rings a bell).

The 7 priority IRQ level 68k's were good. You could mask off any of the IRQ's, 
and a higher priority one would interrupt a lower priority one (Of course). 
WHich means you could drive something low priority at the lowest IRQ level 
(e.g. IRQ driven IO such as serial or parallel port in those days) and use a 
higher priority one for things like the clock... 

They were quite popular in Uni's in the 90's... UnderGrad projects were based 
around them etc... Easy to work with, well understood etc... Great docs of 
course (Back in the days when hardware vendors realised good docs were 
actually handy for ordinary people).

Hamish.
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