Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucsfcgl!pixar!gbuce
From: gbuce@pixar.UUCP (George Buce)
Newsgroups: comp.sys.amiga
Subject: Re: LUCAS board fix (long)(technical)
Keywords: A500/A2000 Reset
Message-ID: <3316@pixar.UUCP>
Date: 14 Mar 89 22:33:58 GMT
References: <3291@pixar.UUCP> <6232@cbmvax.UUCP>
Reply-To: gbuce@pixar.UUCP (George Buce)
Organization: Pixar -- Marin County, California
Lines: 43

In article <6232@cbmvax.UUCP> daveh@cbmvax.UUCP (Dave Haynie) writes:
>in article <3291@pixar.UUCP>, gbuce@pixar.UUCP (George Buce) says:
>> Since we know that the first DTACK* comes from within the Amiga during the 
>> call to ROM directly after reset, and the Amiga specs state that you aren't
>> allowed to return DTACK* before the beginning of S4, we know that the DTACK
>> signal will fall somewhere during the S4 state.  
>
>No, actually, we don't KNOW that (I'm not sure if it's true for an unexpanded
>A1000, but it's not true for an unexpanded A500 or A2000).  The bus master
>(the 68020, in this case) can't ACT on DTACK* before the falling edge of
>S4, which is where DTACK* should be sampled by a device like LUCAS. 
> ---
>With that said, your fix probably has a good chance of working on an A1000
>with no memory added, based on the way DTACK* is actually generated by the
>1000.  With external memory added, there's no guarantee you'll stay synced,

Actually, since we're only interested in re-generating C1* + C3* on the LUCAS
board and only need to sync it once (after the initial reset), I don't see how
the external memory boards can be a problem.  I haven't done any developing
since the A500/A2000 were introduced, but since the autoconfig boards aren't
enabled directly after a reset, I can't imagine that there would be a glitch
during S3.  The only thing we're interested is the *very first call* the 68000
makes to the Amiga, which is going to be a read to the ROM.  Does Fat Agnus
respond with DTACK* during S3?  If so, then my 'U9 fix' won't work on an A500
or A2000 (thought the LUCAS wasn't designed for them...)  Will a soft reset
still generate a call to the ROMs before autobooting off of RAD:?  (Brad,
correct me if I'm wrong, but) The LUCAS board seems to handle refresh wait
state de-synchronisation by extending the wait until it is in sync with an
original S5 state again...

>Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
>   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
>              Amiga -- It's not just a job, it's an obsession

George (8{>

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|...!ucbvax!pixar!gbuce  | Discourager: They don't use Amigas...   8{(        |
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