Author Topic: Anyone here uses an HiDef NES and has these?  (Read 4147 times)

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Offline FrenchyToasty

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Anyone here uses an HiDef NES and has these?
« on: February 18, 2017, 08:10 AM »
No despeckle option help, it's always there... there is a line appearing in some games...



Jason replied to me that it most likely came from a loose connection or a failed PPU or CPU, would that make these visible on AV out too?

« Last Edit: February 18, 2017, 09:24 AM by FrenchyToasty »

Offline FrenchyToasty

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Re: Anyone here uses an HiDef NES and has these?
« Reply #1 on: February 18, 2017, 09:25 AM »
It's visible in AV and RF too... guess I should test some original carts...

Offline iwasaperson

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Re: Anyone here uses an HiDef NES and has these?
« Reply #2 on: February 18, 2017, 10:50 AM »
That's just a part of Mega Man 3. Some games just have that. You can even see it in emulators.
@Syboxez on Discord and some other places as well.

Offline MP2E

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Re: Anyone here uses an HiDef NES and has these?
« Reply #3 on: February 18, 2017, 01:41 PM »
Yep that's completely normal. Happens on an unmodified frontloader NES with the Mega Man 3 cartridge

Offline FrenchyToasty

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Re: Anyone here uses an HiDef NES and has these?
« Reply #4 on: February 18, 2017, 04:35 PM »
Nice, never noticed it, I guess the low res helped.

A comparable line appear in Zelda 2 sometime when I jump or attack. Never noticed such a thing either.

It's so random I can't really show.

Offline MP2E

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Re: Anyone here uses an HiDef NES and has these?
« Reply #5 on: February 19, 2017, 08:07 AM »
Nice, never noticed it, I guess the low res helped.

A comparable line appear in Zelda 2 sometime when I jump or attack. Never noticed such a thing either.

It's so random I can't really show.

That one is quite a bit more tricky: So when the NES or Famicom starts up from power off, the CPU and PPU both start at different times, and there are 4 different possible CPU-PPU alignments on boot up. In a few games including Zelda 2, there's a hardware bug that causes a corrupted scanline to appear at random during gameplay, but only for 2 out of the 4 alignments. So with an unmodified NES you could just press reset until the lines don't appear anymore.

The alignment is completely random on an unmodified NES, But you can actually control which CPU-PPU alignment with the hi-def nes by setting a different 'Despeckle' setting in your menu!

Unfortunately the hi-def NES also makes things slightly more complicated. The clock speeds have to be slightly altered to meet HDMI spec, and the PPU is running in a special digital out mode that was designed for Nintendo Vs Systems and ordinarily inaccessable. This mode works well in general, but on some CPU-PPU alignments, "pixel speckling" occurs on the screen. Usually on 2/4 or 3/4 alignments.

It just so happens that Super Mario Bros, Zelda 2, and many others all have the unfortunate luck of corrupted scanlines on half of the alignments, and pixel speckling on the other half. So you can't really get a 100% perfect picture..

This might not be solvable by the hi-def NES because these bugs are coming from the NES PPU itself. So what to do about these games that force you to choose between speckling and corrupted scanlines?

Technically, they can be ROM hacked into behaving. With all of these games, they end up writing to the PPU_CTRL register to disable more NMIs at the beginning of the NMI routine, to prevent it getting stuck infinitely, then reenable it at the end of the routine. If the game is modified to check a value in RAM instead to see if we already entered NMI, and return if so, instead of actually disabling NMI, the game no longer has corrupted scanlines!

Sorry if that was too technical. The good news is, I've made a patch a while back that fixes Super Mario Bros, so you can see exactly what I mean side by side with the original game
http://krikzz.com/forum/index.php?topic=5585.msg43672#msg43672

I have worked on the other games on and off, but my 6502 skills aren't the sharpest :) Not sure when I'll have another game fixed up. Was working on Zelda 2 but I hit a wall trying to fit the new routine into the old routine
« Last Edit: February 19, 2017, 12:26 PM by MP2E »

Offline FrenchyToasty

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Re: Anyone here uses an HiDef NES and has these?
« Reply #6 on: February 19, 2017, 08:09 PM »
No problem, I like things to be technical, I don't always understand but it pushes me towards more knowledge!

I haven't played too much of SMB on my HiDef NES, I played so much of it as a kid that I now only play like the first few levels and drop it.

What's the issue with Super Mario Bros on HiDef Nes?

I guess playing with despeckle option will resolve these? Like for Double Dragon...
« Last Edit: February 19, 2017, 08:16 PM by FrenchyToasty »

Offline MP2E

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Re: Anyone here uses an HiDef NES and has these?
« Reply #7 on: February 20, 2017, 07:27 AM »
Random corrupted lines in level 1-2 and any underground area basically. Despeckle works for most games but with a few you can't avoid all the minor problems, they need to be ROM hacked to fix them.

99% of the time, just switching the despeckle option should be good enough.
« Last Edit: February 20, 2017, 10:56 AM by MP2E »

Offline FrenchyToasty

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Re: Anyone here uses an HiDef NES and has these?
« Reply #8 on: February 20, 2017, 06:16 PM »
Thanks, I'll patch SMB and continue using the despeckle option on games I see issues.