[Coco] This tickles me....

[Gene Heskett]

On Saturday 25 October 2008, Chuck Youse wrote:
>On Fri, 2008-10-24 at 23:00 -0400, Gene Heskett wrote:
>> V.PAGE?  Yes its used, by the memory manager, and the windowing system
>> IIRC. I believe I also used it in myram. (my ramdisk, in 3rd party tree) 
>> Since myram still works under 3.2.8, I have to assume it is still valid,
>> and not open for grabs.
>
>Hm, I don't see myram.  I also see no references in the kernel, other
>than in IOMan, where V.PAGE is explicitly cleared in the static device
>data area right before INIT is called on any device driver.  (Just
>because I don't see any more references doesn't mean it's not used - it
>just means its not referenced as V.PAGE - i.e., disassembly that never
>got its constants cleaned up or offsets from other fields are used,
>etc.)
>
>Seeing as V.PAGE is supposed to be used as the address extension field -
>for systems that place I/O registers behind address translation rather
>than in front - it's meaningless on a Coco unless you have a multi-pak
>(which has its own address-translation hardware to map different slots
>into FF40-FF5F).  I'm curious why the memory manager gets its fingers
>into that.  I can see why the window manager might want make use of this
>field, but that shouldn't affect non-Window devices (it certainly
>doesn't pay attention to what's in the descriptor; it's always HW.PAGE,
>window devices or not, under Level 2).
>
>It would seem the only reason why the kernel even needs to reference
>this field is to determine which instance of a device driver to invoke.
>I.e., two devices at FF40 with V.PAGE=0 would be e.g., two drives on the
>same disk controller, a third drive at FF40 with V.PAGE=1 would be a
>different instance of the same driver.  It's clear that this was
>Microware's intent, and it's also clear that it was unused on the Coco.
>for some reason no one used the translation ability of the multi-pak and
>instead did address decoding on each board..
>
>Anyway, if you could provide further information it would be
>interesting.
>
>Thanks,
>C.
>
Probably the best description of V.PAGE is in Kevin D.'s "Inside OS9".

My copy is in the basement someplace, and I'm beat from carving cherry all day 
(making an entertainment center, drawers are hell), and am supposed to be at 
the transmitter about 1 AM for the rest of the night so I'm not going to dig 
it out tonight.

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-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Q. Why is this so clumsy?
A. The trick is to use Perl's strengths rather than its weaknesses.
             -- Larry Wall in <8225 at jpl-devvax.JPL.NASA.GOV>