NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/sys/amiga/misc-part1/7980

Internet Message Format | 1996-08-05 | 3.5 KB

Path: EU.net!sun4nl!xs4all!usenet
From: [e-mail] (Jeroen T. Vermeulen)
Newsgroups: comp.sys.amiga.hardware,comp.sys.amiga.misc
Subject: Re: Alpha for A4000/3000 ???
Date: Wed, 13 Mar 96 15:32:06
Organization: Leiden University, Mathematics & Computer Science, The Netherlands
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In article <4hp0bf$[e-mail]> [e-mail] (Michael van Elst) writes:
> [e-mail] (Bernhard Fastenrath) writes:

> >Isn't the ALPHA extremly good at emulating other processors?
>
> No. It is just generally fast, and thus fast when emulating other processors.

There's more to it than that.  The higher-level CPU notions of conventional CPU
design have been moved into a software Privileged Architecture Library (PALcode
for short).  Porting an OS should be easier this way, as you can adapt the PAL
to behave like the processor model your OS was designed for (this is where you
could implement stuff like the 68k condition code register or x86 segments).

Its bi-Endianness also helps emulate different architectures.  The overall
design is very regular and "big" enough in most respects to be used as a
"superset" of another processor by an emulator (64-bit address space, 32 64-bit
registers, 32 fp).  Trap barrier instructions can help emulate more precise
exception models where necessary.

The designers have taken care from the beginning to define a canonical model for
representing integers in different register sizes, so mixing 32-bit and 64-bit
numbers is well-defined from the beginning.  Current implementations support
both IEEE and VAX floating point, but other Alpha chips may drop either (or
both).  The VAX fp was included to help DEC's older clients migrate.

A recent addition (since the 21164A) are partial-word loads and stores, ie.
byte and 16-bit word accesses.  This too should be a lot of help for emulations,
especially to accomodate device drivers and the like.

DEC is also doing a lot of software work w.r.t. emulation on the Alpha:

 - They've written dynamic code translators for MIPS and VAX code (most of VMS
   was initially ported this way).

 - Their UNIX is based on a microkernel, with different "tastes" of UNIX
   implemented as layers on top of its API.

 - An Intel emulator currently in the works (FX!32, memory serving) should,
   according to DEC, deliver "better-than-Intel" performance on the Alpha soon.

Note here that the Intel P6 has the highest official SPECint score on the planet
but is beaten by several competitors on other benchmarks;  as was discovered a
few months ago, more than ten percent of Intel's SPECint rating was due to a
single bug in Intels compiler.  So yes, the Alpha can still be that much faster
in reality yet have a lower SPEC rating.


>                                 Michael van Elst
>
> Internet: [e-mail]
>                                 "A potential Snark may lurk in every tree."

--
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#  Jeroen T. Vermeulen   \"How are we doing kid?"/   Yes, we use Amigas.   #
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