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From: pl@etana.tut.fi (Lehtinen Pertti)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MEMF_PHYSICAL?
Message-ID: <7186@etana.tut.fi>
Date: 25 May 89 08:49:21 GMT
References: <DEVEN.89May24182715@daniel.rpi.edu>
Sender: News@tut.fi
Lines: 71

From article <DEVEN.89May24182715@daniel.rpi.edu>, by deven@rpi.edu (Deven Corzine):
> In article <6966@cbmvax.UUCP> thomas@cbmvax.UUCP (Dave Thomas QA) writes:
> 
>    In article <DEVEN.89May24025106@daniel.rpi.edu> deven@rpi.edu (Deven Corzine) writes:
>    > Fine.  But the RKM's say interrupt code and data MUST be in
>    > MEMF_PUBLIC memory.  Why?
> 
>    I don't know, but MEMF_PUBLIC has never been defined too clearly since it
>    has never done anything.
> 

	I have always thought that idea behind MEMF_PUBLIC is to 
	provide some compatibility with MMU-supported multitasking.
	I protected multitasking systems (like UNIX) every process
	has a address space of its own, and this address space 
	lives and dies with process ( and also swaps to disk).
	Other processes have no access into this space, so
	if we want to install some code (or data) which is
	'outside' this protected address space, we have declare
	it someway. In this case the method would be MEMF_PUBLIC.

	Unfortunately other parts of Amiga system seem to fight
	against this clean idea, but ...


	And to talk about virtual memory.

	I think that one method to provide some virtuality to
	amiga is the way how it is provided in Acorn's (ARM)
	memory controller.

	There MMU divides memory space to three sections:

		000000 - ?FFFFF     virtual ( mapped ) memory
		?00000 - ?FFFFF     physical memory
		?00000 - FFFFFF     IO space


	So in amy we could think something like:

	first 1 M 		Chip ram
	----- 1 M
	next  8 M		physical ram

	Some where ? M		virtual ram

	high mem		IO space

	We allocate portion of phys ram and disk for paging.
	MMU is initialized simply to provide normal address space +
	some virtual ram, normal address space is simply locked into memory.
	Page tables and paging area should probaply be protected
	against unauthorized modifications.

	Question is :
		Is there problems in this kind of layout?

		If virtual mem is addmem'd after boot,
		is there any reason why it woudn't work
		just like normal memory expansion?


					Pertti Lehtinen
					pl@tut.fi


		
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