semi-homemade micro

Jim Battle frustum at pacbell.net
Mon Nov 14 13:33:01 CST 2005


woodelf wrote:

...
> Having got a new PC ... 2 GHZ???  who knows the real speed.
> I have tried Spare time gizmos - pdp 8 emulator  ( A minor bug
> -- with windows  how do you get the bell to sound ?).
> I was running some sort of diagnostics and had the RTC displayed
> and for about 10 minutes of real time, the clock advanced a hour.
> That must be at least 6x faster than the real thing on this computer.

If a 2 GHz (give or take) x86 CPU emulates a pdp 8 at 6x, it means either the 
code is inefficient, or the code contains a speed regulator that doesn't work 
properly.

The original PDP-8 took 10 clocks at 1 MHz to execute one instruction, a 2 GHz 
CPU has 20 million cycles to interpret one instruction.  So at 6x realtime, the 
program is using 3.2 million cycles to interpret one instruction.

Most likely speed and efficiency weren't goals of the emulator, so I bring this 
up not to discredit the program's author but rather to say: don't use that data 
point as anything but a lower limit on what kind of horsepower it would take to 
use a micro to emulate a PDP-8.  I imagine an AVR device at 20-40 MHz should be 
able to emulate a PDP-8 at real time.





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