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Author Topic: Questions about interleaved roms  (Read 2065 times)

Badseed

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Questions about interleaved roms
« on: May 08, 2019, 04:16:34 pm »
Need a little help, trying to run English patched King Colossus: Tougi Ou Genesis rom(patch from this site). The vanilla Japanese rom runs fine, but I only get black screen on patched rom. Using md.emu and unipatcher on my Android tablet.
After trying to research a little and not finding anything but the readme file it may be that I'm using an interleaved rom. Are there any ways to check said rom and de-interleave keeping in mind that I'm using Android therefore can't use any
.exe files. I don't have access to a computer right now.
Thanks in advance for any help
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KingMike

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Re: Questions about interleaved roms
« Reply #1 on: May 08, 2019, 05:58:36 pm »
The fastest way I would check for an Interleaved ROM is to open with a hex editor and look at the Sega header at address $100. There should be visible text that says "SEGA MEGA DRIVE".
(actually it's close enough to the front of the ROM you could probably open the ROM with Notepad and see if there's visible text near the beginning of the file. Just don't save it or anything.)

As to conversion tools, there should be a bunch such as SMD BIN WIN.
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Badseed

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Re: Questions about interleaved roms
« Reply #2 on: May 08, 2019, 08:52:43 pm »
Ok so  SMD is an interleaved format based on 16KB chunks, plus a 512-byte header at the beginning of the file. Each 16KB chunk is interleaved by taking the even bytes, putting them in the first 8K, then putting the odd bytes in the last 8K.
It begs the question why would the devs run SMD BIOS and interleave? Were there performance gains or maybe so basic type of encryption? If the Genesis reads binary why were the two formats necessary? As to what you said King I did find the SMD header at $100. I think I need to find a BIN room to patch.
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KingMike

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Re: Questions about interleaved roms
« Reply #3 on: May 08, 2019, 10:20:35 pm »
If you can read the text properly at $100 then it's probably not interleaved.
(if it is interleaved, you'll only see every other letter, like "SEGA MEGA DRIVE" will become "SG EA RV" or something like that.)
I don't think that interleaving is even a format you could hack with unless you were completely nuts. :D
(unlike the SNES, where I did once hack an interleaved ROM before even knowing it was such.)

There should not be a 512-byte header. The "SEGA Header" stuff is part of the actual ROM data that Sega required developers to put in (and at least part of it was mandatory and required to run games on most actual consoles. Trivia: the western release of Populous doesn't work on most consoles because EA failed to include a Sega header on the game, despite that the game was released a couple years in and so they should've known. They were aware enough at least to put a warning on the box.)
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Badseed

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Re: Questions about interleaved roms
« Reply #4 on: May 09, 2019, 09:55:55 am »
Thanks for the help king. As far as I know you need to convert SMD interleaved to a BIN before hacking. I guess my emulators(tried two different ones) just don't wanna play this patched rom. Oh well was really looking forward to playing :'(
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POWCo-op

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Re: Questions about interleaved roms
« Reply #5 on: May 09, 2019, 11:50:37 am »
You state the rom may be the problem. In that case download the rom from a different site and attempt to patch it. I've been able to play patched King Colossus but I've never tried it on Android.
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Badseed

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Re: Questions about interleaved roms
« Reply #6 on: May 09, 2019, 03:44:58 pm »
Powco-op I've tried roms from several sites all with the same result: the original Japanese language rom plays fine but when patched for some reason I only get a black screen. I wonder if Android may be the problem. Unfortunately I don't have access to a computer right now or I would write some scripts and force an already patched download from a particular now defunct rom site, and see how that works. I just need to keep at it  :banghead:, I got side tracked today trying to get an English version of SD Snatcher for the MSX2 up and running on my droid emulator.
At least I was successful with that.  :woot!:
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