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Author Topic: I'm having a problem with 2 patches.  (Read 2622 times)

Real_Character

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I'm having a problem with 2 patches.
« on: May 08, 2016, 05:48:23 pm »
I'm trying to apply these two patches on a rom through a flash cart:
http://www.romhacking.net/hacks/2351/
http://www.romhacking.net/hacks/2500/

Each one works, but there is only a red screen when I try patching one over the other. One is only a graphical hack, so it should work, in theory. Is there something I'm missing?

MathUser2929

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Re: I'm having a problem with 2 patches.
« Reply #1 on: May 08, 2016, 06:45:16 pm »
Review them badly.

Tito Santana

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Re: I'm having a problem with 2 patches.
« Reply #2 on: May 08, 2016, 06:49:11 pm »
First of all, have you tried applying each patch individually and testing it to make sure there isn't a problem with an individual patch?

Secondly, have you tried to apply them in a different order than what you initially tried?

VicVergil

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Re: I'm having a problem with 2 patches.
« Reply #3 on: May 08, 2016, 06:58:25 pm »
Ohoho, I guess know what's up.  :P
It's the good old dreaded Megadrive red screen of death, isn't it?

That's Sega's anti-piracy scheme.
Megadrive roms have an internal checksum calculated from rom data, and naturally tampering with rom data messes it up. There are tools to fix that checksum whenever modders are done editing their roms.
Besides a wrong checksum, the red screen of death can also be triggered with cheat codes enabled at startup in some cases, with some emulators.

Real_Character

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Re: I'm having a problem with 2 patches.
« Reply #4 on: May 08, 2016, 07:32:59 pm »
Ohoho, I guess know what's up.  :P
It's the good old dreaded Megadrive red screen of death, isn't it?

That's Sega's anti-piracy scheme.
Megadrive roms have an internal checksum calculated from rom data, and naturally tampering with rom data messes it up. There are tools to fix that checksum whenever modders are done editing their roms.
Besides a wrong checksum, the red screen of death can also be triggered with cheat codes enabled at startup in some cases, with some emulators.

Thanks for the tip. That was the problem and it's been resolved. I was even able to add a 3rd patch. I wasn't able to use that application because I'm on Linux, but this worked for me: https://github.com/travistyoj/gen-cksum

VicVergil

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Re: I'm having a problem with 2 patches.
« Reply #5 on: May 08, 2016, 08:24:56 pm »
That's nice to hear. (btw Linux isn't the friendliest environment when it comes to romhacking tools... I hope though I may do something about it once I get somewhat better in programming.)

And if that wasn't clear from my above explanation, I'd also like to add that applying multiple Megadrive patches on the same ROM (smd/gen format) can't not trigger the red screen of death, so anyone quick to review those patches badly might want to reconsider...

That aside, one alternative way not to worry about checksums is to convert the rom to bin format.
Fun trivia: Nintendo too had a checksum protection for the SNES and Game Boy, but it ended up not used to prevent tampered with games from running.

KingMike

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Re: I'm having a problem with 2 patches.
« Reply #6 on: May 08, 2016, 09:38:36 pm »
SNES and GB checksums are not used at all (except for on GB, the header/Nintendo logo protection).
SNES just does not care, so many prototypes will have bad checksums.

Quote
That aside, one alternative way not to worry about checksums is to convert the rom to bin format.
The checksum is part of the ROM header (the internal Sega header), so changing the ROM format wouldn't change whether or not checksum protection applies.
"My watch says 30 chickens" Google, 2018

VicVergil

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Re: I'm having a problem with 2 patches.
« Reply #7 on: May 09, 2016, 12:12:32 am »
The checksum is part of the ROM header (the internal Sega header), so changing the ROM format wouldn't change whether or not checksum protection applies.

It does seem roms in bin fomat have ignored checksum protection when ran on some emulators (Kega, Regen..) though...

Vehek

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Re: I'm having a problem with 2 patches.
« Reply #8 on: May 09, 2016, 01:09:28 am »
Those emulators have "autofix checksum" settings.