semi-homemade micro - test-drb@ccmp.vtda.org

14 Nov 2005

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Subject: Re: semi-homemade micro
   From: woodelf <bfranchuk at jetnet.ab.ca>
   Date: Mon, 14 Nov 2005 13:14:09 -0700
     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at
classiccmp.org>

Don North wrote:

  Doing some math, 2GHz/100KHz is 2000MHz/0.1MHz or
20,000. At 6X the 
 cycle count is then 20K/6 = 3333 (not 3.3M).
 One would think it takes well less than 3000 X86 instructions to 
 emulate a PDP-8 instruction (assuming one instr per clock).
 I would say it takes a few instructions since you have to mask for 12 
bit words, and remember the PC is running windows and all
sorts of other stuff. The point is the emulation is at least 6x faster 
or more compared to
the original.  Faster may not allways be better for emulation. 
With a machine wider than 12 bits the mask is a single instruction AND.
The content of the subfields are more difficult than that but most of
x86s handle bits fairly well.

Allison