Bug in Bob Supnik's Emulator!

[Tim Shoppa]

> 	Not having any great need of an emulated PDP-11 I've not pursued
> 	the (suspected) bug in Bob Supnik's emulator.  Even on a PentiumPro
> 	an emulated 11 is slower than a real 11/73 (and a lot slower than an
> 	11/93 - which I should cease neglecting and stuff a SCSI card into
> 	some day as I did with the 11/73).

On a cow orker's 200 MHz Pentium Pro, Bob Supnik's emulator (compiled
with gcc and running under Linux) is about twice as fast as a real
11/73 for most CPU-intensive operations.  Speeds for I/O based
operations can range from incredibly faster to incredibly slower
than a real -11, of course, and a lot of the interrupt and device
priority schemes seem seriously out of whack with how a real PDP-11
works.  And speed also depends on whether the MMU
is enabled or not, too.

The same emulator running on a 7-year-old 133 MHz DEC Alpha is about
a third the speed of a real 11/73 (slow enough that a lot of 60 Hz
line-time-clock interrupts go uncounted under RT-11, for example!)

Tim.

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