[rescue] systems with user modifiable microcode.

[Greg A. Woods]

[ On Wednesday, October 2, 2002 at 13:00:03 (-0500), Scott Newell wrote: ]
> Subject: Re: [rescue] The aesthetics of rescue
>
> I've read the some of the VAX or PDP machines also had user modifiable
> microcode.

The PDP-11/60 has a microcode option.  I think it is the only one of the
PDPs that had such a feature.  I'm not sure about VAXen.

>  Did anyone ever use it (custom microcode) for anything?  

I'm sure I've read papers of people using the 11/60's microcode option
for nifty application specific performance enhancements.  The 11/60 I
first used Unix on had the option IIRC, but it was unused.

> Is the (PALcode?) for Alpha similar to writable control store?

Nope.  In this case PALcode stands for "Privileged Architecture Library
code".

Alpha PALcode provides an abstraction layer to the hardware which makes
it easier to port an OS to variations of the platform.  It's sometimes
different for each OS since each might have different requirements.

It's all documented in the hardcopy "Alpha AXP Architecture Reference
Manual":

  http://www.support.compaq.com/alpha-tools/documentation/current/alpha-archt/alpha-architecture.pdf

and here:

  http://www.support.compaq.com/alpha-tools/documentation/archive/sdk/ec-qfglc-te_palcode_sys_dsgn_gde.pdf

>  Again, does
> anyone ever modify it?

You sometimes have to write your own PALcode if your OS needs different
services than that supplied in the commonly available PALcode.

-- 
								Greg A. Woods

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