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Oh the resolution sucks but everything is psycoldelic and half there....perhaps like if one could fry a 7800... or something...other carts are playing fine... I cleaned the cart...(it plays fine in the old 7800)...that didn't help, shouldnt be the 7800 contacts because other games have no problems... :sad:


Desert Falcon,

Mrs. Pac-Man,


Midnight Mutants

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ok....can someone walk me through that?


(finding the part that's acting up)


1) it happens at random times

2) it only so far happens on choplifter

3) the game is still roughly playable but only half rendered

4) sound still works

5) is gives WWII warthog looking jets, micro chopper and psychedelic tank

6) the middle of the top of the screen is unreadable the base is split lateraly across the screen and its nearly impssible to find the helipad

7) Explosions are pschedelic slow and flash all one color 5 or so colors

8)all the baddies are easier to see, especially the UFO ... The collision detection works as if full size

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Funny, how his chop lifter is doing EXACTLY the same thing that the choplifter rom will do in emulation from time to time in MESS. Actually I haven't tested Chop Lifter for some time in MESS. But I can remember a year or so back, this would happen.


Now, I only mention this, because if we can find out what in MESS emulation was causing this, it might help lead the direction to what in his actual 7800 might be causing this? Or is this just a general issue where Chop Lifter will look this way on any 7800 with some minor bad components?


Just a thought...

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Can someone tell me just what is wrong in that picture? Is it really making those circular moire patterns, or what?


I will say that in my first attempts at 7800 programming, I found that forgetting to set the stack at startup could cause some wierd problems. The stack pointer is initialized to $16 by the boot ROM. Using the stack for JSR/RTS would somehow cause the screen to break up with herringbone patterns. This is wierd for a couple of reasons:


1) The RTS shouldn't have worked in the first place, because the 7800 maps $0100-$013F to the TIA and MARIA registers. It would have just read mirrors of the collision registers. The game (in this case the tank demo which I had typed in from the Monitor Cart docs) was clearly still running in spite of the screwed up screen. I downloaded a copy of the Monitor Cart to my CC2, and was unable to get the $116 area to read back what I poked there. But by messing around in the $116-$11A area, I was able to sometimes get the screen to break up.


2) $116 may be firmly in the TIA area, but it's in the audio registers area. That shouldn't cause the TIA to go unblanked.


3) The herringbone pattern was out of sync with the Maria, as it made wavy vertical and diagonal bars. They were wide enough to have been TIA sync bars, though.

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Bruce, you have an old version of MacMESS right?

Try running Choplifter in it, you'll probably see the same graphics glitchs that he is talking about. This has been fixed in newer of version of MESS but MacMESS hasn't been updated in a while.



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Better pitures no strange circles...


(@ Mitch -she...this one is female ;) )



one of these has a hostage, hostage camp, and tank, the other pict is the base... also the color on start up is blue instead of green when this is going to happen, it now seems to happen at an "event" like running into the UFO or shooting a jet or self opening a hostage camp. The other is 'normal' before anything happened.




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Those look EXACTLY like the graphics glitching that would occur in the older versions of MESS. I am not a programmer...other than the Java 1 class I was required to take. (Java appears to be all they teach in college anymore?!). So I don't know what was fixed in MESS to correct this. But if it was a timing problem...then that timing problem in the emulation is actually happening here on real hardware. What in the emulation was fixed to correct this? Because whatever registers weren't right and such to cause this, would lead to where the problem might be on real hardware.


But basically, those shots look exactly like Choplifter running on older versions of MESS.

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I have two 7800, one I just got from a recomended trader who I hope gets back to me and the other one my parrents had since it came out. It works fine on mine the new one it does this after awhile... 5-20 min approx maybe something is getting too hot?

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I'm kind of ignorant when it comes to hardware, but it really seems from those screenshots that the MARIA is confused about how to render the graphics data, like maybe its in the wrong read mode or something. The graphics are crunched horizontally like its drawing in hi-res, and the colors are distorted, which would happen since hi-res colors are mapped differently than they are in Choplifter's proper graphics mode. The other garbage on the screen could happen from errors reading the display list, that could happen if the maria is having faulty reads from ram during its DMA cycle, or if the internal line ram is having problems. I doubt the system ram is faulty since that should cause more problems than just graphics.


The MARIA is probably the most likely candidate for an overheating problem I would think. I suppose you could try opening the case and blowing a fan over it and see if that keeps the problem from occurring. Still, I don't see why this would be the only game causing a problem. Maybe its an obscure glitch that happens to be triggered by Choplifter and only happens when something gets too hot? Dunno... but I guess I'd try to determine if its heat related.

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I found this in xmame-0.82.1/mess/vidhrdw/a7800.c line 384:


   /*  moved start of vblank up (to prevent dma/dli happen on line -4)

       this fix made PR Baseball happy

       Kung-Fu Master looks worse

       don't know about others yet */

   if( frame_scanline == ( a7800_lines - 4 ) )


       /* vblank starts 4 scanlines before end of screen */


       maria_vblank = 0x80;


       /* fixed 2002/05/14 kubecj

               when going vblank, dma must be stopped

               otherwise system tries to read past end of dll

               causing false dlis to occur, mainly causing wild

               screen flickering


               games fixed:

               Ace of Aces

               Mean 18

               Ninja Golf (end of levels)


               Impossible Mission




       maria_dodma = 0;

       /*logerror( "vblank on line %dnn", frame_scanline );*/




I'm not sure how this would affect real hardware, since it should be impossible for anything to be drawn during vblank. The only reason that's an issue in an emulator is because the vblank is synthetic.[/code][/i]

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oops, ignore my comment after that code. The original problem was not that it was drawing anything during vblank. The problem was that it was causing invalid interrupts to occur, and those interrupts caused random changes to the maria registers during vblank, which subsequently screwed up how things were drawn on the next frame.

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Did you figure out if it's a heat related problem? If it is, I suppose you could attach a heatsink to the chip, but it might just keep getting worse no matter what you do. I've never fixed an Atari so I'm really just guessing. For all I know the maria might not even be the problem.

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