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  • Joined: 04 Aug 2020
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  • Location: Ontario, Canada
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Does checksum / region matter?
Post Posted: Wed Aug 12, 2020 2:32 am
I posted a translation patch yesterday, but I realized I never bothered to patch the header. However, I can't seem to find any SMS emulator that cares about the checksum.

I was trying to find documentation about what happens if a checksum fails. I saw statements that some BIOS revisions don't check it at all, and that some do, but I couldn't find anything that says what happens if it fails. Does it just display a message, or refuse to run the game?

Same question for region byte, will it refuse to run on a BIOS that doesn't match?

If it does matter, I suppose I'd assume that an Everdrive probably automatically patches the header on load just to make sure game ROMs easily run on whatever system they're in?

If that's the case maybe it doesn't matter at all. I'm sure if somenoe wanted to make a dedicated repro cart of it, they would be capable of fixing the header themselves anyway, and I can't think of another situation where it would come up? Do I have that right?
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  • Joined: 14 Aug 2000
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  • Location: Adelaide, Australia
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Does checksum / region matter?
Post Posted: Wed Aug 12, 2020 3:36 am
Yes it does. A real system will display the "Software Error" message and refuse to run the game.

Read about it here: https://www.smspower.org/Development/BIOSes
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  • Joined: 04 Aug 2020
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Post Posted: Wed Aug 12, 2020 3:44 am
Thanks.
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Post Posted: Wed Aug 12, 2020 6:29 am
Some emulators have options to boot via the BIOS and these will fail.

I would suggest also adding an SDSC header to help label the version and attribution, even if it is a bit more invasive.
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Post Posted: Wed Aug 12, 2020 7:50 am
rainwarrior wrote
I posted a translation patch yesterday, but I realized I never bothered to patch the header. However, I can't seem to find any SMS emulator that cares about the checksum.

I was trying to find documentation about what happens if a checksum fails. I saw statements that some BIOS revisions don't check it at all, and that some do, but I couldn't find anything that says what happens if it fails. Does it just display a message, or refuse to run the game?

Same question for region byte, will it refuse to run on a BIOS that doesn't match?

If it does matter, I suppose I'd assume that an Everdrive probably automatically patches the header on load just to make sure game ROMs easily run on whatever system they're in?

If that's the case maybe it doesn't matter at all. I'm sure if somenoe wanted to make a dedicated repro cart of it, they would be capable of fixing the header themselves anyway, and I can't think of another situation where it would come up? Do I have that right?

In Emulicious you can select which BIOS to use and with an Everdrive OS you can also test compatibility with Everdrive.
So you can test different configurations to see if they work.
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