Re: Accelerator / VGA Graphics card

[mjmahon@aol.com (Michael J. Mahon)]

Sheldon Simms wrote:

>On Fri, 24 Oct 2003 14:59:39 -0400, Charlie wrote:

<snip>

>> That makes sense and I like the idea of the 1MHz clock generating an
>> interrupt on the card.  Wouldn't this free up the emulator to do other
>> things (graphics) in between interrupts?
>
>Well yes, but it would probably do everything it needs to do and then
>still be waiting around.

Have you checked out how long the Pentium M requires to take an
interrupt and restore state and return?  I'll bet that caches are much
less helpful for this than you imagine, and _lots_ of cycles are needed.

>> And even if there was nothing to do, from the little I've read about
>> the Efficeon chip it drastically reduces its power consumption when
>> it idles.
>
>So does the Pentium M. This sort of idling won't save too much power
>though, because it wouldn't happen except when the card needed to
>access the bus -- disk, DOC, flipping soft switches, etc. And
>most programs spend only a small amount of time doing that stuff.

And if you speed the processor execution up by a factor of, say,
25x, then the time spent doing these low-speed things does not
accelerate, and the fraction of time doing low-speed things rises
proportionately.

For example, if a real Apple II running program X takes 10% of its
time doing things like disk I/O, then even if the processor is
accelerated infinitely, the program runs only 10x faster, since
all of its time is now spent on disk I/O.

-michael

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