[Simh] Representative Instruction Execution Timing

[Matthew J Fletcher]

On 05/04/11 15:47, Dalby, Jeremy R (GE Power & Water) wrote:
> I am trying to figure out how to slow down the SIMH PDP-8 simulator such
> that the instructions are executed with similar timing to that of a real
> PDP-8.  I have found that that even with throttling set very low, the
> PDP-8 simulator executes much, much faster than a real PDP-8.
>
>> From what I have read, I believe the execution of a single PDP-8
> instruction can take anywhere from 1.2 - 4.6 microseconds, depending on
> the type of instruction and I/O device to which the instruction applies.
>
> I am running the PDP-8 simulator on a Windows XP host, which I
> unfortunately cannot change to a real-time environment.
>
> Some things I have considered:
>
> 1.  Inserting a sleep() function after execution of each PDP-8
> instruction, but this won't work since the minimum sleep time is 1
> millisecond, and even a 1 ms sleep request is not likely to return for
> at least 20 ms due to Windows non-real-time scheduling.

Do you have to use a Windows host ? We use usleep() on Linux and its 
normally accurate to 10% of the specified sleep interval. Thats on both 
x86 workstations (Dell T3400 etc) and ARM (i.MX25) SOC's.


regards

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Matthew J Fletcher
amimjf(at)sky.com
www.amimjf.org
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