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Author Topic: Mega Drive patches with wrong checksum  (Read 3192 times)

Alcahest

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Mega Drive patches with wrong checksum
« on: November 01, 2019, 01:53:11 pm »
Hey all,
I tried all the English patches from the MD translation section and the following roms end up with a wrong checksum:

- Dahna - Megami Tanjou (Japan) v1.0 by cccmar

- Dynamite Headdy (Japan) v070428 by M.I.J.E.T.

- Fushigi no Umi no Nadia (Japan) v1.1 by KingMikeTranslations

- Panorama Cotton (Japan) v1.0 by Malias

- Psy-O-Blade (Japan) v1.1 by EienNiHen

- Sonic Eraser (Japan) (SegaNet) v1.0 by D

- Star Cruiser (Japan) v0.991 by NebulousTranslations

I tried contacting the patch creators but most have no contact info (expect cccmar, M.I.J.E.T. and Malias to whom I fired a mail).
How would I go about contacting the other authors to let them know about the issue?
« Last Edit: November 01, 2019, 02:00:11 pm by Alcahest »

EvilJagaGenius

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Re: Mega Drive patches with wrong checksum
« Reply #1 on: November 01, 2019, 03:16:15 pm »
Probably the better option is to use a tool to fix the checksum yourself, like this: http://www.romhacking.net/utilities/342/
Some emulators have options to auto-fix the checksum too, if you're using one.

Alcahest

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Re: Mega Drive patches with wrong checksum
« Reply #2 on: November 01, 2019, 09:15:01 pm »
Thanks, yes I found this tool, along with this one https://www.romhacking.net/utilities/1344/
and I certainly can fix them on my end but I thought authors would be interested too (in order to release fixed patches, etc..).

For instance all of M.I.J.E.T. MD patches generate roms with correct checksums except Dynamite Headdy, which I found odd.

KingMike

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Re: Mega Drive patches with wrong checksum
« Reply #3 on: November 02, 2019, 02:59:17 am »
I know there are some Genesis games that, even unmodded, have a bad checksum.

Not sure if anyone has bothered to make a list.
Retrode has noted Blaster Master 2 as one example.
I can't recall if Zero Wing has a "bad" checksum (as I know both regions have the effective ROM size wrong in the header). (that is, if the checksum matches either the wrong 512KB size or correct 1MB size.)
MegaPanel is another I know, as I have personally dumped my cart a few times to check, even tried overdumping it with the same result.
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FlashPV

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Re: Mega Drive patches with wrong checksum
« Reply #4 on: November 02, 2019, 05:40:36 pm »
By the way, I couldn't get Dynamite Headdy working. I'm using Kega is it an emulator problem?

Alcahest

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Re: Mega Drive patches with wrong checksum
« Reply #5 on: November 02, 2019, 08:00:47 pm »
@KingMike, interesting, and these still run on original hardware of course ?

By the way, I couldn't get Dynamite Headdy working. I'm using Kega is it an emulator problem?

Possibly, make sure the source rom (JPN) has MD5:
cdb36911439289d3453060f58682057c

And the generated rom should be:
d43cd7d31616d2992e3b1ac389ef4eb1


TheGershon

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Re: Mega Drive patches with wrong checksum
« Reply #6 on: November 03, 2019, 01:36:31 am »
I have roms with those checksums too and fixing the header actually makes it NOT work. It plays fine without doing so on Genesis Plus GX.

KingMike

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Re: Mega Drive patches with wrong checksum
« Reply #7 on: November 03, 2019, 02:14:39 am »
@KingMike, interesting, and these still run on original hardware of course ?

I don't THINK the original console TMSS verifies the checksum, just checks for things like the "SEGA" text?

(different than some developers, such as EA, who wrote self-verification routines into the games)
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Alcahest

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Re: Mega Drive patches with wrong checksum
« Reply #8 on: November 03, 2019, 09:09:40 pm »
I don't THINK the original console TMSS verifies the checksum, just checks for things like the "SEGA" text?

(different than some developers, such as EA, who wrote self-verification routines into the games)
Yeah TMSS mustn't be verifying the checksum, most likely. Apparently only certain roms perform a self-check, not the whole library.

Btw Malias released a fix patch for Panorama Cotton's checksum :)

November 07, 2019, 05:55:44 pm - (Auto Merged - Double Posts are not allowed before 7 days.)
For M.I.J.E.T.'s Dynamite Headdy, turns out the bad checksum is intentional.
Quote
This game uses a non-standard method to calculate the checksum.
If the checksum really is bad, you'll get the "red screen of death".
« Last Edit: November 07, 2019, 05:55:44 pm by Alcahest »