Path: utzoo!attcan!uunet!cs.utexas.edu!rutgers!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Motherboard revision differences
Message-ID: <13018@cbmvax.commodore.com>
Date: 3 Jul 90 18:32:27 GMT
References: <4060@uqcspe.cs.uq.oz.au> <12955@cbmvax.commodore.com> <[2688b902:593.2]comp.sys.amiga.hardware;1@wcbcs> <8439@uhccux.uhcc.Hawaii.Edu> <12414@june.cs.washington.edu>
Reply-To: daveh@cbmvax (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 42

In article <12414@june.cs.washington.edu> dylan@june.cs.washington.edu (Dylan McNamee) writes:
>In article <8439@uhccux.uhcc.Hawaii.Edu> olson@donald.uhcc.Hawaii.Edu (Todd Olson) writes:
>>	My 4.3 with a 1-meg Agnus works with my 2630..sorta.
>>Upon guru the screen will go blank, no guru message, just a blank screen,
>>when I then three finger salute, I  get the guru, then one more three
>>finger salute to get back to working order.  

>What Todd describes is exactly the behavior I have experienced with
>my _brand new_ 2500/30.  (6.x I forget the rev.)  I have been 
>assuming this had something to do with the '030 cache or something.
>(I do use SetCPU.)  Does anyone know the official word on this?

This isn't a problem with your A2500, either old or new.  It's the effect of
a crash upon the system when you're relocating the system ROM with SetCPU.

The deal is this.  SetCPU starts up, allocates a big chunk of memory, moves
your ROM image into it, builts the appropriate MMU table, turns on the MMU,
and all of a sudden you're hauling butt with a 32 bit ROM.  Good deal, eh?
Only, along comes a system error of some kind.  Along with system errors
come system resets, via the 680x0 RESET instruction.  The problem is here --
when the OS resets the system, that's a CPU-generated reset that only will
reset system devices, not the CPU.  While the MMU registers are a member of
the CPU set, the memory that your really fast ROM image runs from is a 
member of the device set.  So the RESET yanks the OS out from under itself
by resetting your autoconfiguring memory.  The three-finger reset is a hard
reset, which will kick both devices and CPUs back to their reset state, and
so the system wakes up then, finds the GURU it wanted to tell you about, and
reports it.

The 2.0 system handles this situation better, by providing a Reset() call
in exec.  This allows a program such a SetCPU to create it's own Reset()
function that will safely shut down the MMU prior to issuing the soft
RESET.

>dylan mcnamee
>dylan@cs.washington.edu


-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
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	"I have been given the freedom to do as I see fit" -REM