Re: [stella] behold, i am become shiva, destroyer of kernals!

Subject: Re: [stella] behold, i am become shiva, destroyer of kernals!
From: Christopher Tumber <christophertumber@xxxxxxxxxx>
Date: Thu, 11 Mar 2004 02:18:26 -0500
I *think* the problem may be that you're not initilising your stack properly. You init with:

Start
        sei     
        cld     
        txs     
        ldx #$FF        
        lda #0          
ClearMem 
        sta 0,X         
        dex             
        bne ClearMem    

Which will result in your stack being set to whatever X is at startup. So your stack may well be overwriting your variables. Uhh, maybe not, I don't see any subroutines so your stack is doing SFA except skipdraw (In which case you really don't need to be preserving the stack if ever need the saveStack byte for something else). At any rate, shouldn't it be:


Start
        sei     
        cld     
        ldx #$FF        
        txs     
        lda #0          
ClearMem 
        sta 0,X         
        dex             
        bne ClearMem    

Nope, doesn't fix the problem but maybe worth mentioning anyway...

Chris...


At 05:00 AM 11/03/2004 +0000, you wrote:

>So, I am learning some basic page boundary issue detection 
>skills, but this one has me stumped.  (Yeah, I know, big surprise.)
>I am getting better at isolating and noticing this kind of thing,
>honest...and for every bit that seems likely to be timing-sensitive,
>I align 256 it or at least use a CHECKPAGE macro around it.
>
>So, like usual with this kind of thing (at least, with the kind of 
>thing I think this might be, I'm not quite certain :-/   )
>the problem showed up when fixing something else, a causal
>relationship is assumed, disproved when it messes up even with 
>NOPs in the recently worked on code...then I started shoving NOPs 
>around, figuring if I moved the NOP pair to after a certain properly 
>bit and it started to work, then maybe that was the bit that 
>needed page boudary attention. 
>
>So, I found a crucial point, a single STA insruction, two NOPs immediatley
>or some distance before kills everything, two NOPs immediately or some 
>distance after, no problem.  And it seems to be 
>NOWHERE NEAR anything time related...looking at the .lst file, 
>it's not near any particular page boundary. (And of course, this
>is only on a (supercharged) atari...it's fine and dandy on Z26
>and PCAEwin.)
>
>Here's the working and broken source code, respectively:
>http://alienbill.com/joustpong/20040310.source.ok.txt
>http://alienbill.com/joustpong/20040310.source.broke.txt
>
>search for the term "shiva", it indicates where I empirically
>determined (the? a?) breaking/no-breaking point to be.  
>
>I am so grateful for this group.  This game NEVER could have 
>happened, ever, without you guys.  You've let a semi-ok high level
>programmer have a great time bringing his 2600 dreams to life.
>I'm just praying for one more miracle from you guys , because I am 
>SO close to being done...I found this while fixing a bug where
>I forgot to change the criteria for flashing P2 score during 
>Poorlords, so there's that, there was one slightly scary case 
>I MIGHTa saw, where the ball bounced off a wall but no chunk
>of wall disappeared (I was actually quite proud of how I isolated
>that bug before, but maybe some case of it was missed or re-emerged),
>and MAYBE I'll try touching up the physics and effective AI, but 
>that's IT, I'm so close to ready for Philly...
>(Oh, and maybe I should look into eliminating flash when reset is 
>hit. But that's it!)
>
>Oh, Eckhard: re the title screen.
>It's Z26 (2.09) -- June 22, 2003 -- you mentioned it was 265, but
>according to my version of Z26 it was 266...but that wasn't the more
>standard 262, so I fixed it...and then that seemed to help with the 
>problem I was previously describing, wher it'd say 1 Line, 1300+
>FPS, I haven't seen or heard that problem since.  So maybe at some
>point it might be interesting to see what Z26 does w/ odd scanline 
>counts? I'm not sure.
>
>A bounty of a free t-shirt to anyone who can tell me what
>this is and how to fix it!
>
>Thanks always,
>Kirk
>
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