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Re: Memory Management w/o MMU" [message #91353] Thu, 07 November 1985 23:16 Go to next message
bruceb is currently offline  bruceb
Messages: 41
Registered: October 1985
Karma: 0
Member
Article-I.D.: amiga.206
Posted: Thu Nov  7 23:16:50 1985
Date-Received: Sun, 10-Nov-85 08:32:47 EST
References: <370@caip.RUTGERS.EDU>
Reply-To: bruceb@hunter.UUCP (Bruce Barrett)
Organization: Commodore-Amiga Inc., 983 University Ave #D, Los Gatos CA 95030
Lines: 18
Keywords: multitasking loader


Yes, the "executable" files include relocation information.  This
info is used to relocate code when it is loaded.  Code doed NOT move
around once loaded.  Please note, however, that not all of the code
(and data) need to be contigious.  So small peices of code/data go
into small memory chuncks, larger ones into large chunks.

In Version 1.0 (first customer release) and before the loader would
try to use the "cheapest" memory available, so if you had >512k your
program would get loaded there.  This (extended memory) is not available
to the custom chips so you need(ed) to copy any grahpics / sound info
down into the first 512k.  (After appropriate allocation of memory...)

In Version 1.1 (not yet available) we hope to have the loader
and development environment set up so that you can load segments of
your code in the memory type of your choosing.

--BruceB
Re: Re: Memory Management w/o MMU" [message #123499 is a reply to message #91353] Tue, 26 November 1985 12:38 Go to previous messageGo to next message
tim is currently offline  tim
Messages: 230
Registered: February 2013
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Article-I.D.: ISM780B.39700009
Posted: Tue Nov 26 12:38:00 1985
Date-Received: Fri, 29-Nov-85 08:55:40 EST
References: <371@sdcc13.UUCP>
Lines: 17
Nf-ID: #R:sdcc13:-37100:ISM780B:39700009:000:555
Nf-From: ISM780B!tim    Nov 26 12:38:00 1985


 >  GET THIS THRU YOUR HEADS OR TAKE AN OPERATING SYSTEMS CLASS:
 > 
 >  THE BARE MINIMUM NEEDED FOR MULTITASKING ARE PROCESSOR
 >  INTERRUPTS OCCURING AT INTERVALS, AND AN INTERRUPT HANDLER.

But it isn't SAFE to do it without an MMU!  I want to be able to
run a random C program and not have to worry about crashing the
damn machine!

The MMU does not have to be fancy.  A simple MMU that divides the
address space of a process into, say, 256 equal size pages would
be fine.  This is simple to build.

						Tim Smith
						ihnp4!cithep!tim
						ima!is780!tim
Re: Re: Memory Management w/o MMU" [message #123530 is a reply to message #91353] Wed, 27 November 1985 10:47 Go to previous messageGo to next message
dca is currently offline  dca
Messages: 24
Registered: May 2013
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Article-I.D.: edison.618
Posted: Wed Nov 27 10:47:07 1985
Date-Received: Sat, 30-Nov-85 01:09:04 EST
References: <370@caip.RUTGERS.EDU> <371@sdcc13.UUCP>
Organization: General Electric Company, Charlottesville, VA
Lines: 23

 >  You know, I am getting sick of all these 'how do you do
 >  multi-tasking without an MMU' questions.
 >  
 >  GET THIS THRU YOUR HEADS OR TAKE AN OPERATING SYSTEMS CLASS:
 >  
 >  THE BARE MINIMUM NEEDED FOR MULTITASKING ARE PROCESSOR
 >  INTERRUPTS OCCURING AT INTERVALS, AND AN INTERRUPT HANDLER.
 >  
 >  
 >  Larry J. McCaughey

This is true but, it is also like saying all you need to make a fire
is two wooden sticks.  It is unfortunate with all its sophisticated
hardware that the amiga didn't use a system that would provide inter-task
protection and I certainly wouldn't have complained about virtual memory.
Can't say as I blame them, however, virtual memory hasn't made a big
splash in personal computers, the lack of multi-tasking operating
systems in personal computers has not educated very many of their
users in the difficulties of multi-task debugging, and
the 68k series MMU isn't supposed
to be too quick anyway.

David Albrecht
Re: Re: Memory Management w/o MMU" [message #123592 is a reply to message #91353] Wed, 04 December 1985 22:14 Go to previous message
guest is currently offline  guest
Messages: 22
Registered: May 2013
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Junior Member
Article-I.D.: ccivax.336
Posted: Wed Dec  4 22:14:33 1985
Date-Received: Sat, 7-Dec-85 04:43:25 EST
References: <370@caip.RUTGERS.EDU> <371@sdcc13.UUCP> <618@edison.UUCP>
Organization: CCI Telephony Systems Group,  Rochester NY
Lines: 30

 >>  GET THIS THRU YOUR HEADS OR TAKE AN OPERATING SYSTEMS CLASS:
 >>  
 >>  THE BARE MINIMUM NEEDED FOR MULTITASKING ARE PROCESSOR
 >>  INTERRUPTS OCCURING AT INTERVALS, AND AN INTERRUPT HANDLER.
 >>  
 >>  
 >>  Larry J. McCaughey
 >  
 >  This is true but, it is also like saying all you need to make a fire
 >  is two wooden sticks. 
 >  It is unfortunate with all its sophisticated
 >  hardware that the amiga didn't use a system that would provide inter-task
 >  protection and I certainly wouldn't have complained about virtual memory.
 >  
 >  David Albrecht

It's Ironic that that the Argument used to support putting the OS in ROM
(Both ST and AMIGA) is considered irrelevant when discussing an MMU.
Amiga contains a complicated WCS (Write Control Store) to manage the
kickstart disk, yet assumes that memory protection between applications
is not needed.

AMIGA - Don't put the OS in ROM or WCS, just put an MMU between the 68000
and the rest of the RAM.

MULTI-TASKING WITHOUT AN MMU IS LIKE DRIVING A CAR WITH NO BRAKES.

Opinions are mine, but I'm giving them up for adoption.

rb@ccivax
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