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Re: GO-NET Mega Drive (SEGA MegaModem) [Re: BigFred] #91262 11/05/13 12:04 PM
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Originally Posted By BigFred
Hello everyone,

as I announced on no-intro already I have dumped GO-NET for the Japanese Mega Drive. I want to make sure it is a complete and useful dump before selling. When dumping in auto-mode using the retrode I receive a 512k file which loads fine in Kega. However when I force to dump as 32 MBit I get 4xthe 512k mentioned above and the 2nd half (2 MB) consist of 4x 512k of different data though there appears to be nothing of importance here. I still like to know what I have here. Is there any way to play Mega Modem dependent games in MESS or other emulators? Any other suggestions or anyone who might want to analyze it? Thanks in advance.


The upper 2MB area is probably mapped to SRAM and what you see there is SRAM data being mirrored.
Even if opening the cart is obviously the best, a lot of stuff can be guessed from analysing the ROM or looking at the cartridge connected pins, do not worry ;-)

Btw, what method did you use for dumping ?
Also how far can you go with the ROM in an emulator ? Can you even start a game or does it absolutely need modem hardware to be detected ? The modem hardware is very unlikely going to be fully emulated but it shouldn't be complicated to analyse the software and figure what you need to emulate to make it go further. Modem was connected through the back exp port i guess ? The game manual probably has some nice picture about that.

Originally Posted By ReadOnly
I'm not harsh lol, at all, try to imagine a world with only undocumented roms, patch factories are what 'emus' would be. Such indulgence is the reason why we have so much mess lying around, I'm talking about the web garbage collections, no pun intended (maybe?).


That's quite exagerated, for cartridge with only ROM and even SRAM inside, you does not need to see the board schematics for perfect emulation. Sure it's better for preservation purpose to know the exact number of mask ROM chips, their size, etc... But it has absolutely NOTHING to do with ROM-specific hacks in emulator...

Last edited by Eke; 11/05/13 12:10 PM.
Re: GO-NET Mega Drive (SEGA MegaModem) [Re: BigFred] #91263 11/05/13 12:08 PM
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Hello BigFred, long time not seeing you. smile
The GO-NET modem seems to be a rare piece of hardware.

Re: GO-NET Mega Drive (SEGA MegaModem) [Re: BigFred] #91267 11/05/13 02:18 PM
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Originally Posted By BigFred
Seriously: If you want to risk destroying a 1600 game that's your decision but I still have some sanity left in my mind.


There was no much point in acquiring that piece of rare hardware then, because your rom alone is not going to accomplish much.

Originally Posted By Eke
That's quite exagerated, for cartridge with only ROM and even SRAM inside, you does not need to see the board schematics for perfect emulation. Sure it's better for preservation purpose to know the exact number of mask ROM chips, their size, etc... But it has absolutely NOTHING to do with ROM-specific hacks in emulator...


That's quite inaccurate my good friend, those carts are so much more than just the rom image in your zip files and if they work as is, it's because the emulation is completely inaccurate and relies on mechanisms the hardware never used. This is true for each and every cart, but even truer for carts with additional and/or rare hardware capabilities and this cart has most certainly both of those. In that case even more than in others, releasing a binary image alone is not accomplishing much, it's important to stress this out, yes.

Re: GO-NET Mega Drive (SEGA MegaModem) [Re: BigFred] #91268 11/05/13 02:23 PM
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Was the modem inside the cartridge like the X-Band or is this only a cartridge that drives a modem connected someplace else? Because in the former case ReadOnly is not wrong.

Re: GO-NET Mega Drive (SEGA MegaModem) [Re: Eke] #91269 11/05/13 04:13 PM
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The Modem is an external piece of hardware attached to the Mega Drive that several other games and some banking software make use of. Otherwise I would't have bothered to get my hands on this game. Actually I believed/hoped that as long as the file is complete and unaltered it would be enough for a proper emulation (I didn't know if the Modem is emulated). Here is an article by ElBarto:

http://www.elbarto.org/index.php/2012/05/the-megadrive-modem/

An explanation that most games work as peer to peer and should still be playable:

http://www.sega-16.com/forum/archive/index.php/t-15793.html

Using a flashcard with this method you could possibly verify that it is complete and useful. But who owns all this equpiment :S

Of course I'd have liked to provide more detailed info but what can you do? You wouldn't go into a museum and burn all pictures just to receive information you wouldn't receive otherwise. The original is still as important as the copies.

@ElBarto

Of course - I can also provide the manual - maybe it's useful in some way.

Originally Posted By Eke

Btw, what method did you use for dumping ?
Also how far can you go with the ROM in an emulator ?


I used the retrode 1 with software 0.18c. The game loads in Kega for instance and you can browse through the menus. However after pressing start there is a message that

"the transmission protocol data in the save memory has been damaged, damaged portion has been initialized"

- thanks to Cowering & Co. for that translation.

Then you have an option to initialize the save memory. And yes I think that the data in the 2nd half is SRAM - actually it's 64k that repeat over and over again till the end - not 4x512k.

Re: GO-NET Mega Drive (SEGA MegaModem) [Re: ReadOnly] #91270 11/05/13 04:22 PM
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Originally Posted By ReadOnly
those carts are so much more than just the rom image in your zip files

I am perfectly aware of this and never said the contrary but...

Quote:
and if they work as is, it's because the emulation is completely inaccurate


...actually IS very exagerated. For traditionnal carts, the only thing that MIGHT be inaccurate is the way the ROM binary is mapped and eventually mirrored in the 68k address space but:

1) using commonly used ROM mapping will work because most of the time, it is how it is mapped in the cartridge so it IS accurate guessing. If the cartridge used uncommon mapping or banking hardware, the emulator would fail at running it anyway.

2) emulating ROM mirroring is fairly easy to accurately figure as well without opening the cartridge (by dumping the whole memory range area or by looking at connected address pins on the connector, when possible). That's said mirroring is generally ignored by the cartridge software so it's not a big deal and absolutely unnoticeable.

Off course, this only applies to simple cartridge hardware with only ROM and maybe also SRAM (for which similar guessing for mapping and mirroring can be made) but saying that every undocumented ROM dump out there relies on inaccurate emulation to work is not true.

And actually, even for more complex cartridge hardware, stressing the cart andanalysing the ROM can generally give you very accurate and complete informations of the memory layout. I reverse-engineered the SMW64 pirate cartridge by just disassembling dumped data and poking at the cartridge port, the board itself with all its epoxy blobs was fairly useless.

Quote:
and relies on mechanisms the hardware never used.
I don't understand what you mean by that, and, as emu developper, it actually does not make much sense to me. What "mechanisms" are you thinking about ?

Quote:
This is true for each and every cart, but even truer for carts with additional and/or rare hardware capabilities and this cart has most certainly both of those.


I am pretty sure this is not the case here and you
will only find a common 512K mask ROM and 32K Backup RAM. That game is like San San, it uses the Mega Modem which was sold separetely, that cart is way too small to embedd anything like that. Off course I might be wrong but all I am saying is that it is not necessarily needed to open it in order to accurately emulate the cartridge hardware, in which case the binary dump is fine. Emulating Mega Modem hardware is another story off course, but opening the cart won't help you there either.


Quote:
In that case even more than in others, releasing a binary image alone is not accomplishing much, it's important to stress this out, yes.


Documenting cartridge boards is important yes, but dismissing the efforts made to acquire that cart and dump the rom is quite ungrateful in my opinion. It serves as data preservation and without it, precious board scans are useless anyway.

Last edited by Eke; 11/05/13 04:29 PM.
Re: GO-NET Mega Drive (SEGA MegaModem) [Re: Eke] #91271 11/05/13 05:01 PM
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Originally Posted By Eke
Quote:
and relies on mechanisms the hardware never used.
I don't understand what you mean by that, and, as emu developper, it actually does not make much sense to me. What "mechanisms" are you thinking about ?
Here's a very simple example which you can test easily. Take almost any retail snes image, blank out the header, flash it and you'll see it will work exactly the same way on real hardware, but on most emulators out there... BAM!! it most likely won't work properly going from minor problems you might not notice such as bad sram size to no boot at all. Because a real snes does not pick infos on the header to adapt its functions, the cart just works by its hardware layout.

Only two emulators have made significant progress on that front, MESS & bsnes. Why? Because carts pcb are being documented. The pcb layout is a crucial factor in A LOT of aspects : rom size, rom map (driving), saving capability, ram size, supplementary hardware, protection (lockout), etc... all of them being 'theoretically' unpredictable if not documented, even some nintendo approved headers were proven to be wrong and you have all the non approved headers of course.

Just look at the very point of this thread : the rom size! Why playing guessing game when you can have solid evidence and documentation. As a dev, do you prefer to have to guess the hardware or to have a clean picture of it?

Besides you also need to look forward and think about the elements which could be required on a lower level emulation someday. No documentation of these elements = forget completely about a lower level.

There's so much more to be said but I wasted already too much time on this.

Originally Posted By Eke
Documenting cartridge boards is important yes, but dismissing the efforts made to acquire that cart and dump the rom is quite ungrateful in my opinion. It serves as data preservation and without it, precious board scans are useless anyway.
We will agree to disagree my dear friend for I believe they at best serve distributing free to play (and rather crappy) games or adding mindlessly to rom stat numbers, that's not preservation friendly and should be dismissed as a way to promote higher standards.

Re: GO-NET Mega Drive (SEGA MegaModem) [Re: BigFred] #91272 11/05/13 05:20 PM
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Originally Posted By BigFred
The Modem is an external piece of hardware attached to the Mega Drive that several other games and some banking software make use of.
Are there pictures of a disassembled modem somewhere?

Re: GO-NET Mega Drive (SEGA MegaModem) [Re: ReadOnly] #91274 11/05/13 08:59 PM
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Originally Posted By ReadOnly
Here's a very simple example which you can test easily. Take almost any retail snes image, blank out the header, flash it and you'll see it will work exactly the same way on real hardware, but on most emulators out there... BAM!! it most likely won't work properly going from minor problems you might not notice such as bad sram size to no boot at all. Because a real snes does not pick infos on the header to adapt its functions, the cart just works by its hardware layout.


Again, i never denied that such information is very important to preserve and that it can help dealing with overdumps, problematic games, etc... I was just responding to initial simplistic statements saying that without cartridge board layout being documented, existing dumps were meaningless and emulation was necessarely inaccurate or bound to game-specific "hacks". For the Mega Drive at least (which this thread is initially about and is very different from SNES), the header is not used or even needed for proper ROM mapping (only sometime for SRAM mapping actually, in which case it is accurate for the majority of games) and the standard memory layout can be applied to the majority of existing games without sacrifying accuracy of cartridge hardware emulation.

Originally Posted By ReadOnly
Only two emulators have made significant progress on that front, MESS & bsnes. Why? Because carts pcb are being documented. The pcb layout is a crucial factor in A LOT of aspects : rom size, rom map (driving), saving capability, ram size, supplementary hardware, protection (lockout), etc... all of them being 'theoretically' unpredictable if not documented, even some nintendo approved headers were proven to be wrong and you have all the non approved headers of course.


And it's a very respectable and understandable goal but it does not change the fact that a specific game must somehow be recognized by the emulator, be it using an external or internal database. In your previous example, what would happen in said emulators if you remove your SNES header and try to load it ? There are big chances it won't work because CRC or whatever is used to identify it will not match any known ROM. Actually, removing ROM header like you said probably is a bad example and won't work on real hw either because it most likely still holds some fields that are used by console hardware (exception vectors,..) or game software (internal checksum,..) like it is the case for MD.


Quote:
will agree to disagree my dear friend for I believe they at best serve distributing free to play (and rather crappy) games or adding mindlessly to rom stat numbers, that's not preservation friendly and should be dismissed as a way to promote higher standards.
In my opinion, software preservation is as much important as hardware preservation and, from experience, you can learn equally from both with reverse-engineering. You can have more interest for the latter and I would also prefer having a scan of the cartridge board but if it is not possible then so be it, acting as if you were some kind of quality standard authority, and the dumper some kind of useless ROM kiddie, was actually rude.

Last edited by Eke; 11/05/13 09:05 PM.
Re: GO-NET Mega Drive (SEGA MegaModem) [Re: BigFred] #91275 11/05/13 10:34 PM
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Originally Posted By BigFred
@The proposal with the X-ray was interesting though I fear it won't be possible - but I will try. Seriously: If you want to risk destroying a 1600 game that's your decision but I still have some sanity left in my mind.

Do it if you can. It probably won't let you identify the components, but you can see chip locations, pin counts, die sizes, and PCB traces. If you get it at a bit of an angle you can trace out a double-sided PCB. It'd be easy enough to identify a common board layout.

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