[rescue] systems with user modifiable microcode.

[Greg A. Woods]

[ On Wednesday, October 2, 2002 at 16:53:52 (-0400), Dave McGuire wrote: ]
> Subject: Re: [rescue] systems with user modifiable microcode.
>
> On Wednesday, October 2, 2002, at 04:46 PM, Greg A. Woods wrote:
> >>    The 11/03 does as well.
> >
> > Hmmm... I have one of those!  :-)
> 
>    Do you have the WCS option?  I know they exist, but I've never seen 
> one.

No, I don't think I have the WCS option for an 11/03 -- unless maybe
it's installed in one of the dead units (I actually have three 11/03
board sets, and I think only one potentially working one installed a
BA11, with the other known-dead system being a "little" 3U (IIRC)
chassis that I can't remember the model number of).

>    I was under the impression that PALcode instructions weren't regular 
> Alpha-instruction-set instructions.  If they are, then ignore my last 
> statement. ;)

Yup, the subroutines are composed of just more or less regular code, and
usually it's just loaded in main memory by the firmware at boot.  There
are a few (5 IIRC) opcodes that are reserved for PALcode use only.  They
do things like really low-level chip state manipulation (which is, I
think, where the "privileged" part comes in), and of course to help in
the transition back from the PALcode mode environment (which is entered
by hardware inputs, or by invoking a PALmode instruction, or with
call_pal) to the native mode where the OS takes over again.  Sometimes
if your native mode code just jumps off into random data it'll encounter
such an opcode and since it's running in native mode it triggers an
OPCDEC exception.

When I got my first DEC Multia and heard about PALcode I thought it had
something to do with "programmable array logic" -- after all I knew it
couldn't be "PDP Assembly Language"!  :-)  Finally one day I used the
"dict" utility to look up definitions for PAL and finally learned:

  From V.E.R.A. -- Virtual Entity of Relevant Acronyms December 2001 [vera]:

  PAL
          Privileged Architecture Library (DEC, Alpha)

and then my whole view of the Alpha and OS support for the Alpha changed
significantly!  :-)

To me I find it makes the most sense to relating PALcode and PALmode to
the IBM RT's VRM (Virtual resource manager), though there are dangers in
such an analogy given that the VRM was much more ambitious and much
slower (it was very poorly implemented, even though it was a "Good Idea")

	http://www.computer-museum.ch/IBM/ibmrt.htm

-- 
								Greg A. Woods

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