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From: scc@cl.cam.ac.uk (Stephen Crawley)
Newsgroups: comp.arch
Subject: Re:  Re:  Re: MicroVAX emulation
Message-ID: <690@scaup.cl.cam.ac.uk>
Date: 23 Mar 89 02:07:00 GMT
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> HOWEVER, the MICROvax architecture does NOT include string instructions, 
> other than MOVC3 (and MOVC5?).  

There is no such thing as the MICROvax architecture.

According to the VAX architecture manual, there is a VAX architecture
with 4 defined subsets:
  Full VAX ... i.e. everything
  Kernel subset
  MicroVAX I subset
  MicroVAX chip subset
  
In the same chapter they also write:
  Also, the combination of hardware and instruction emulation routines
  in the operating systems must (as required) give the appearance of
  a complete architecture on all processors.

All members of the VAX family including microVAXes are sold as implementing
the VAX instruction set ... either in hardware or in software.

> Some DEC-supplied software includes emulation to ease the transition.

No.  There is clearly no concept of a transition involved ... if you
go by what DEC say in the VAX architecture manual.

> Generating the in-line emulation using a reduced instruction set is NO 
> PROBLEM, right? 

Provided you have source to the compiler and skilled effort available,
it boils down to "time == money".  But I could name a few places that 
won't sell source code for any price that WE can afford.  [I'm not talking 
about MIT ... who give CLU compilers etc away free to academic institutions]

> And gets better performance too?  :-)

Obviously.  Of course you emulate the functionality you require rather
than emulating the MATCHC, SKIPC, SPANC etc instructions.

> MIPS, AMD, Intel, Motorola, Sun, etc. don't do your work for you either.
> I don't understand why it is OK for the RISC suppliers to supply
> reduced instruction sets, but if DEC does it it's evil.

Now you are talking about compilers here.  [I hope] MIPS, AMD, etc. would 
not object to you using one of their compilers to cross compiling and 
running code on a bare processor.  I'm happy to pay for the s/w licenses 
for the cross development system. 

The difference between RISC manufacturers and DEC is that with the former
I only need a s/w license for the machine that I run the compiler 
on, while with the latter I need a s/w license for ALL machines.

Another difference is that MIPS, AMD, etc always made a big thing of you
buying their RISC compilers, whereas in the case of the microVAX subsets,
it is in the fine print.

I'd also be happy if DEC unbundled the emulation source code and sold it 
separately for its true value.  I just cannot accept that the true value 
of the emulation code is identical to that of (say) a full Ultrix license.

=====

OK ... so maybe I'm being unrealistic here.  In the real world, anything 
goes so longs as it is not illegal.  Screw the client for as much as he
can pay.  That's the advantage of a free market.

Perhaps if we academics sold the results of our efforts back to industry 
at their true market values we could afford to carry a few rip-offs.

Disclaimer:  These are my own views, not those of my employers.