[Coco] CoCo 3 MMU test for all

[Arthur Flexser]

Roger, the value you get from reading an MMU address depends on exactly HOW you
read it, I discovered some years back.  This arose when I noticed that the value
I got from PEEK differed from the value returned by the MON function in ADOS (ML
monitor).  I traced this to the fact that PEEK used something like LDA 0,X while
MON used LDA ,X.  The different postbyte affected whether I got $7x (PEEK) vs.
$3x (MON).  So, I think asking people to PEEK an MMU address and report the
results will give you a somewhat misleading impression.

Art


On Sun, 20 Jan 2008, Roger Taylor wrote:

> 
> Since LOADM does read what you poke in any address, including the MMU 
> registers, I can take advantage of a few things if I know more than I 
> knew before.  ;)
> 
> For the record, most of what you guys are assuming I don't know, I've 
> known for years.  I'm not a hardware guy like you so I wouldn't care 
> why Tandy only used 6 of the 8 MMU bits so we would be having these 
> conversations 20+ years later about ghosting and how other designers 
> handled adding another 1.5 megs.
> 
> I realize 128k on a memory board is $0-$F and my question about Why 
> Tandy uses MMU blocks $30-$3F was not asking how ghosting works, it 
> was me making a point that the software point of view is all I'm 
> interested in here.  If PEEKing 65441 yields $79 because %01000000 
> shows up on an undesired/illegal PEEK, my initial idea was that Tandy 
> did this on purpose.  It really doesn't matter to me now.  The topic 
> is blown far away from my original post, as this happens from people 
> only reading the first sentence and then jumping back with tutorials 
> and stuff.  All of my stuff works great and I'm about to load huge 
> games into both 128k/512k CoCo's from a single .bin file.  On a 1 or 
> 2 meg CoCo 3, I'm sure I'll have different copies of the .bin file 
> that will LOADM without producing an error.
>