Re: 6502 illegal opcodes questions

[pausch@saaf.se (Paul Schlyter)]

In article <bruce#fanboy.net-628A67.09374025052006@news.newsreader.com>,
Bruce Tomlin  <bruce#fanboy.net@127.0.0.1> wrote:

> In article <e53i7m$1set$1@merope.saaf.se>,
>  pausch@saaf.se (Paul Schlyter) wrote:
> 
>> The Java platform doesn't exist in hardware - it must be simulated
>> in software.  "But that means Java is portable: I can run my JVM on
> 
> I thought Java bytecodes, or at least a significant portion of them, 
> actually had been implemented in hardware.  But I know for certain that 
> UCSD P-code had been implemented in hardware once at least once in the 
> mid '80s.  I think it was called the "P-Engine", and Jerry Pournelle 
> mentioned it in his column in Byte.
> 
> Likewise, I recall that a significant portion of Smalltalk bytecodes and 
> primitives were implemented in hardware at Xerox, using the Dorado's 
> capability for downloadable microcode.
> 
> So just because someone makes up an instruction set for a virtual 
> machine doesn't mean that it can't (or won't) be implemented in 
> hardware.  There may be a few of the more complicated instructions that 
> have to be trapped out and implemented in terms of the less complicated 
> instructions, but if someone feels a need to do so, it can get 
> implemented in hardware.  (So when is someone going to take up the 
> challenge and implement Zork's instruction set in VHDL?)

Yes, there have been some processors which runs Java bytecode directly.
But they weren't successful.

Western Digital's Pascal Microengine was an attempt to make a CPU which
ran UCSD Pascal P-code directly, as you pointed out.  But that too was
unsuccessful.

Another attempt was Intel's first 32-bit CPU, the iAPX-432.  It
consisted of a few chips, and ran Ada "P-code" directly.  But that too
was unsuccessful.

The reason of the failure of these CPU's was bad performance.  Soon after
Intel released the 80386, it stopped producing the iAPX-432:  the 80386
ran much faster.

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