Different BIOS versions do not behave as expected when ran

[NeRdTheNed]

After remembering how cool the Japanese BIOS for the Master System is, I thought I'd pull it up with Clock Signal. To my dismay, only a black screen showed up, and the Space Harrier theme was nowhere to be heard :( The European / American v1.3 BIOS booted fine, and so did the Japanese version of Fantasy Zone I tested. However, my curiosity got the better of me, so I tried running other BIOS files, and the results did not disappoint.

(US/European BIOS v3.4 with Hang On. It appears to be trying its hardest to be a Japanese BIOS instead, but with no FM sound and very broken graphics. It otherwise seems to run, including the PSG sound, and the text changing colours over time.)

I have no clue what's wrong, and I wish you the best of luck diagnosing this issue! A useful resource might be this article on BIOS revisions for the Master System, and this article for the included checksums of these BIOSes.

[TomHarte]

I'm also at an immediate loss, but it's likely to be a recent regression, likely when I was trying to improve the machine's efforts to boot without a BIOS — https://www.youtube.com/watch?v=8mLS0Mz00VM shows the Japanese BIOS just a couple of months ago.

I'll stick my nose in shortly.

[TomHarte]

I think I've got a handle on this: the emulator doesn't correctly recognise BIOS-containing .sms files. So I don't handle the complete range of that file format correctly. My testing of the BIOS was formally installing it and starting a machine without a cartridge, which is a whole other use case.

I'll try to fix it this weekend.