From: Villy Madsen [Villy.Madsen@shaw.ca]
Sent: Monday, October 16, 2006 10:38 PM
To: Info-VAX@Mvb.Saic.Com
Subject: SimH VAX emulation with throttling

Greetings all..

1) The throttled version of SimH VAX and ancillary stuff is available at
http://members.shaw.ca/Villy.Madsen/simh/ or at
http://68.150.97.212/simh/ (but this one isn't always up - it's an emulated 
VAX)

2) Here's how it works....
-  The throttled version of the SimH uVax3900 emulation has a code snippet 
added to it that adds a 1 millisecond wait every N times 400 emulated 
instructions.  If (N == 0) or (N>=1000) then the sleep code is bypassed.

-  The value of N is updated whenever the emulated register at (IOPAGEBASE + 
015200) is updated.

- A program running at priorty 12  and with sysprv under the emulated VAX 
wakes up every few seconds and tallies the total CPU utilization for all the 
processes.  It decreases the value of N if the total CPU utilization is less 
than 25% (slowing the emulation down) and increases the value if the total 
CPU utilization is greater than 50% (speeding the emulation up).  On my 
1.5ghz P4 running XP, I have the minimum value (a system wide logical 
"THROTTLEMIN" ) set to 20  (in other words a 1ms sleep every 8000 emulated 
instructions) which equates to less than 1% utilization on the P4 and a 
vupometer value of 1.1.  with "THROTTLEMIN" defined as 1000 (i.e. disable 
throttling) the VAX emulator uses 100% and has a vup rating of 6.2  (I 
know - it doesn't make any sense).

- Warning - the IO addresse is defined in the DN-11 emulation software. 
Running throttle on the standard SIMH Vax (or the 11/780) or on a real vax 
will cause a machine check....  (I'll fix that one of these days)

Any questions ??

Villy

Villy