Checksum: 34629
Path: utzoo!utgpu!anakin
From: anakin@gpu.utcs.toronto.edu (Anakin Research)
Date: Wed, 15-Mar-89 14:47:58 EST
Message-ID: <1989Mar15.144758.12325@gpu.utcs.toronto.edu>
Organization: University of Toronto Computing Services
Newsgroups: comp.sys.amiga
Subject: Re: LUCAS board fix (long)(technical)
References: <3291@pixar.UUCP> <6232@cbmvax.UUCP> <3316@pixar.UUCP>
Reply-To: anakin@gpu.utcs.UUCP (Anakin Research)
Keywords: A500/A2000 Reset

>>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...
 
Yes George, you are correct! LUCAS can startup on the wrong side of the 
C1+*C3 cycle. and your fix corrects that problem. Once your in sync, the 
circuitry on the LUCAS board takes care to sync up to the S5 state as
you surmised. This is a startup problem which appears to affect about
10% of the Amiga's out there, judging by the reports I receive. I have
yet to have someone with this problem not have it eliminated by your fix. 
Turning the machine off and on again a couple of times also works, but
that's pretty tacky.
                                        Brad