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  • Joined: 26 Jul 2016
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Master System Checksum Fixer
Post Posted: Wed Apr 19, 2017 8:46 pm
Hey, a fellow user on Sonic Retro suggested that I post this here.

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Since I'm currently working on some Master System stuff and I've wanted to try and advance my C programming abilities for a while now, I've made a program to fix the Master System's checksum as the BIOS won't run the ROM otherwise, making it cumbersome for ROM hacking. Just drag a file and drop it, or include it in your batch scripts.

Post any bugs you have here.


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  • Joined: 19 Oct 1999
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Post Posted: Wed Apr 19, 2017 9:25 pm
Hmm, we've avoided making that for years to avoid people polluting romsets with "fixed" roms (e.g. for SG-1000 and Japanese games), and it's a two-byte manual fix if you want to do it yourself. However, we are in an age of 8-bit romhacks by less technical people who may find this helps them.
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  • Joined: 26 Jul 2016
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Post Posted: Wed Apr 19, 2017 10:25 pm
Yeah, the fixes for the Japanese ROMs wasn't my intention, more so that the checksum wouldn't have to be altered with every subsequent build with any code alteration, something I found to be a nuisance when working on homebrew for it.
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Post Posted: Thu Apr 20, 2017 6:56 am
WLA DX emits correct checksums. Any devcart with a loader (Everdrive) doesn't need the checksum.
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Post Posted: Thu Apr 20, 2017 7:33 pm
Huh, fair enough. I don't use WLA for assembling Z80 myself, and I can't say I knew about the current devcart omitting the checksum. Nevertheless, it's here if people want to use it, I guess. :A
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Post Posted: Sun Jul 28, 2019 1:45 am
Dandaman955 wrote
Huh, fair enough. I don't use WLA for assembling Z80 myself, and I can't say I knew about the current devcart omitting the checksum. Nevertheless, it's here if people want to use it, I guess. :A


Hey Daniel,

I needed this to check the checksum of some ROM dumps I found in compilations, and I've removed the writing support to make it into a checker which can run under Linux.

I'd like to make those changes public, but I wonder under which license your work was. Under which license would this work be?
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Post Posted: Wed Jul 31, 2019 12:26 am
I don't think he's going to see your message, but I happen to be his friend on Facebook so I tried to give him a heads up. What happens now is beyond my control, I'm afraid.
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Post Posted: Wed Jul 31, 2019 12:33 am
Tom wrote
I don't think he's going to see your message, but I happen to be his friend on Facebook so I tried to give him a heads up. What happens now is beyond my control, I'm afraid.


Appreciated, thanks!
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Post Posted: Wed Jul 31, 2019 12:52 am
I came back to edit my post with a follow-up, but you were faster than me :P

Anyway, to my surprise, he already replied on Facebook, saying that he's going to look at your post tomorrow, so expect something to happen.

I'm glad I could help.
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Post Posted: Thu Aug 01, 2019 10:54 pm
Hey, you're going to have to excuse me because I haven't really been keeping up with programming in the past year, and I'm not particularly familiar with licenses. Feel free to do what you want with the code, the source is on GitHub.
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Post Posted: Thu Aug 01, 2019 11:31 pm
Dandaman955 wrote
Hey, you're going to have to excuse me because I haven't really been keeping up with programming in the past year, and I'm not particularly familiar with licenses. Feel free to do what you want with the code, the source is on GitHub.


Much appreciated. I've uploaded the new version to:
https://github.com/hadess/smssum
and gave it a free/libre license so any changes to it get shared.

Thanks for this useful tool.
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