Weird EMS Cart issue - ROM check fail (Page 1 of 2)

I have EMS 64M (from Nonfinite electronics) since 2011 and i have no problems with it, even backup battery is still first, at first page is only LSDJ and at second some additional chiptune tools and even games. Little problem was when i upgraded to Windows 10, because drivers are not MS certified and must be installed on that special boot mode for betatesting. I backup my LSDJ tracks monthly and try if everything is loaded fine in emulator BGB

What the heck is ROM check? I personally think that EMS 64M flash cartridge is rock-solid made because i have had no issues with it, but you can *probably* try other Gameboy if same happens, i sometimes also switch cartridges between mine DMGs

That linked article is excellent, but formulation is not accurate, because ROM cannot be rewritten, maybe eprom or these flash nand technologies. During my time with LSDJ i had once occurance, where one track was not loaded properly, it was mistaked in some patterns, but it was battery in my gameboy, when i changed it to new all was loaded properly, luckily.

Last edited by martin_demsky (Dec 19, 2018 7:19 pm)

During my time at electrotechnical high school my teacher told me that rom can be written only once, and eprom rewritten also only once (Erasable Programmable Read-Only Memory), so logically rom chips are used for pernament things on computer boot, like core of OS, basic interpreter, core routines to communicate with basic devices like disk drives, tapes, or printers on 8255 parallel port etc.

But i know what U mean Nitro ))

And sorry for little offtopic, i hope that Kal has found solution to his question.

Last edited by martin_demsky (Dec 20, 2018 11:26 am)

When in doubt on things like this, always trust nitro, even over college professors. Dude knows his stuff

UPDATE: I have fixed the issue!

Simply enough, all it took was me uploading an older sav file.

I wonder why the sav file was messing up the ROM check??

Now THAT is a weird issue.

Anyone with the same issue I've had - clear or revert the sav to an older version.

Sadly, I lost a couple weeks of progress, but it's something I can get back to with some time. I should start backing up more than once a month..

To be fair, he's technically correct. (The best kind of correct as some people say.) But the use of the word ROM is colloquially acceptable in the context, and arguing that it's absolutely wrong, in my opinion becomes pretty much a hypercorrection.

Here's the deal with the checksum check: The check is done whenever LSDj detects an incorrect signature in the save data under the assumption that this also means that the cartridge is being used for the first time. But this also means that the check is performed if the save RAM got corrupted. And it also means that if you write a working save file to SRAM, LSDj considers the cartridge to already be initialized and skips the check. So it's possible both to get false negatives and false positives compared to the intended outcome of the test.

But what's more, the checks relies on a particular behavior in the memory mapper (MBC) on the cartridge. A typical Gameboy cartridge ill expose two 16k areas, one that will always be bank 0, and one where the program can select any ROM bank. However older MBCs (MBC1-3) would select 1 if you asked it to select bank 0, because selecting bank 0 would mean that the same ROM bank is visible in two different places in the memory map. The newer MBC5 does not have this behavior, and selects bank 0 when asked to. LSDj's checksum relies on the fact that bank 0 is selected when writing bank 0, which is the newer MBC5 behavior.

Some emulators, as well as some flashcarts, implement the MBC1-3 behavior, which also causes this error. The latest version of LSDj should fix this so it works on either type of cartridge, so upgrading might be a good idea.

So the question is, which type does your EMS64 cart behave as? Here's a ROM for testing this. It will also test the whole ROM image for corruption, but that's not what's interesting here. You're looking for what it says after MBC type. Could you please write this to your cartridge and see what it says after MBC type? If it says MBC1/3 that explains the mystery. If it says MBC5, then it truly is a mystery.

http://www.gg8.se/temp/verifyrom-mbctest.zip

Btw, if you thought to make a backup of the RAM data before writing new data to the cartridge, I might be able to recover the songs that were ost.