Re: LZ: Re: A few questions, a few comments, blahb
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Re: LZ: Re: A few questions, a few comments, blahb
On Tue, 9 Oct 1996 22:11:20 +0000, you wrote:
> (1) It is too slow. Instructions are executed much faster (I=20
>think a few hundred instructions per second, but correct me if I'm=20
>wrong.) than the link port can handle (a few thousand bytes per=20
>second).
>
Actually, the processor executes at about a few hundred *thousand*
instructions per second. At a 6 Mhz clock, this makes each T-State
about 0.0000001 seconds, and with about 7 to 12 T-States making up the
average instruction, were looking at almost a million instructions per
second (1 MIP)! Of course, this pales in comparison to modern
processors, but it's surely fast enough for our purposes. Your right,
though, because every time you would want to fetch the next
instruction from the expander, you would have to wait almost 10,000 T
states to execute it! Talk about a slow down...
> (2) It is not possible to snag the attention of the processor after=20
>each instruction, except to add a wire inside. Even if this was=20
>done, the processor would be forced to run at the speed of the link=20
>port (see above).
>
I don't even think it would be possible by adding traces. In a Z80,
there are two request lines, the memory request line and the IO
request line. The IO request line goes low every time you access a
port, which doesn't just happen when we want to access the link port.
That line is also called when you access the timers, the screen, the
keypad, etc. It would be an impossible mess to distinguish where the
interrupt came from if we directly tied IOREQ to the IRQ line! Oh
well, it doesn't really matter anyways.
-Mel
<pre>
--
The TI-85 Memory Expansion Homepage
http://pilot.msu.edu/user/tsaimelv/expander.htm
</pre>
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