Date: Fri, 09 Oct 1998 18:51:08 -0700 From: Jason Thorpe <thorpej@nas.nasa.gov> To: David Seifert <seifert@sequent.com> Cc: alpha@FreeBSD.ORG Subject: Re: PALcode Message-ID: <199810100151.SAA07944@lestat.nas.nasa.gov>
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On Fri, 09 Oct 98 16:25:44 PDT David Seifert <seifert@sequent.com> wrote: > The PALcode customises the machine for a particular OS. > That is the whole point of the PALcode. > There is PALcode for Unix, PALcode for VMS, and PALcode for NT. > > Similar deal with the console software. > SRM for VMS and Unix, ARC or AlphaBIOS for NT. > > ARC cannot read a BSD disklabel. Right, basically, the NT PALcode is just totally alien, as far as UNIX is concerned: - Interrupt semantics are different. - VM semantics are different (makes the Alpha a lot like a combination of MIPS and x86... "funny that!" ... including limitation to 32-bit address space, user and KSEGs, 2-level page table traversal a'la x86, etc.) - All the traps are different. - The process (i.e. HWPCB) structures are different. What it comes down to is this: "An Alpha with NT PALcode is a different processor architecture." The instruction set may be the same, but basically everything you have to deal with at the low-level in an operating system is different. Side-note: it's somewhat amusing/scary how non-x86-centric NT actually is at the bootstrap level... For example, on the x86 and on the PowerPC, NT requires a glue layer on top of the native console software on that platform (i.e. PC BIOS or OpenFirmware) that emulates the old MIPS ARC console... I have no doubt that deep in the guts of the x86 HAL, there is code that emulates e.g. the MIPS KSEG by direct-mapping the memory in the system probably by using the large-page support in modern x86 CPUs. Jason R. Thorpe thorpej@nas.nasa.gov NASA Ames Research Center Home: +1 408 866 1912 NAS: M/S 258-5 Work: +1 650 604 0935 Moffett Field, CA 94035 Pager: +1 650 940 5942 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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