Date: Thu, 04 Feb 1999 20:48:26 -0800 From: Jason Thorpe <thorpej@nas.nasa.gov> To: Peter Wemm <peter@netplex.com.au> Cc: Stuart Krivis <stuart@apk.net>, freebsd-alpha@FreeBSD.ORG Subject: Re: alpha PC Message-ID: <199902050448.UAA06189@lestat.nas.nasa.gov>
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On Fri, 05 Feb 1999 11:54:24 +0800
Peter Wemm <peter@netplex.com.au> wrote:
> etc. In the console code is embedded a copy of "palcode". Palcode is
> both a blessing and a curse. It's the low level pseudo-microcode that
> provides a personality for the execution environment. It is meant to
Ah ah ah! It's not microcode! Remember, this is a RISC system! Thar
be no microcode here!
What really sets PALcode apart is that it is written in the standard
Alpha instruction set. It *does* use some facilities only avalable to
PALcode, e.g. the hw_* instructions (which are different from Alpha
processor model to model) and the IPRs (internal processor registers).
But, it's really just a program, much like a kernel, which runs at a
higher privilege level (PAL mode).
> The NT palcode basically tries to make the Alpha look as much like a PC as
> it can get away with.
Well, sort of a cross between PC and MIPS :-) NT, even on the i386, requres
a "veneer" program which presents a sort of ARC-like console :-) NT is
a lot less x86-centric than a lot of people think.
> restore the 64 bit environment or something like that. It can then run
> Unix-like OS's that were intended to run under a SRM environment and real
> OSF palcode with a lot less pain than trying to run in a
> sanitized-to-avoid-confusing-NT environment.
err, OSF/1 PALcode environment. There's at least one commercial Alpha
system which ships with a non-SRM console, but has OSF/1 PALcode.
-- Jason R. Thorpe <thorpej@nas.nasa.gov>
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