In battletoads the method used is arbitrary data manipulation, not arbitrary code execution. There's some period where battletoads executes open bus, which can theoretically be manipulated to look like it's executing sensible commands, but it's very hard and no one feels like doing it.
Ho, ok, I'm happy than you explain this. If I understand well, I can change the BIOS especially if i use a specific game (JPN...)? It's more accurate to use the original BIOS or just for more proper? Thank you for information.
Cool run, this is a rare games who put up "SEGA MASTER SYSTEM" before game starts. Musics are good and when I watch this TAS, i feel like in a "shoot them up"! It's a good illusion. yes vote
On the contrary. On Z80 the R register is 0 at reset. So on emulators now without BIOS, they start at 0. However with BIOS, this register will increment. So regardless of cycle accuracy, this register won't match based on BIOS or not. It has nothing to do with emulation accuracy. And many games use this register as part of randomness routine. Except this isn't how one would usually play these games...they'd use the original machine, not a copy of the BIOS of that machine on a different machine...
What about the Model 1 Genesis/Mega Drive? Did that have any kind of a BIOS for SMS games?
Ok I fixed it, turns out gambatte was turning on the screen in the initial conditions, so writes to VRAM were getting blocked. Now just a little more cleanup and I should be able to add this as a capability to BizHawk.
What I did was having the DMG bootstrapper in an array, and then choosing based on register 50 which array to read when accessing the ROM region of the memory map. Basically, that should have worked. EDIT: If you can share your code, I could maybe have a look?
Well I tried putting a boot rom loader in gambatte, I got it loading but I got a buggy result. I'm not really sure what its doing to get the title messed up like that, but doing the obvious thing of swapping out the first 256 bytes of the rom with the bios obviously is not sufficient. Oh well, I don't think I'll put any more effort into it, maybe once gambatte is replaced someday we'll have native suppport for it.
The issue of version will need to be decided. Because bootup times between versions vary, games using the R register in randomness calculations can result in very different outputs. Other than what could be copied into RAM with different BIOS versions, I'm not aware of any other impact BIOS will have. But these two are already very important. v1.3 is the most "common" and the first / original retail version. These are arbitrary points for using it as a base. But what if the TAS is for a built-in game in a later BIOS? Should there be exceptions for this case? I would hope it isn't a "fastest BIOS" search... but who knows, maybe some game has an exploit that is more useful with a certain BIOS version? I've done some testing on console with Alex Kidd in Miracle World on a v1.3 USA unit and found, if I remember, about 16 possible variations of randomness in powerups. None of these variations matched the emulator. I would need to test again to see if I delayed the emulator to match the frame count of the console...I don't have any notes about that written down.
The Game Gear and Model 2 Genesis/Mega Drive have a BIOS file in the form of a Trade Mark Security System.
Do current TAS emulators for GB/GBC even allow starting runs from BIOS? If not, that obviously would need to happen first before we can do anything. Even if it is, it will be hard to strictly enforce turning on BIOS for Game Boy runs, at least in any short term manner. It's like deprecating an emulator, and such processes typically take a long time (easily several months or years) for all TASers to transition through.
Adding GB(C) BIOS support should be easy, I've done it with an emulator I wrote. I can hold the hand of anyone that wants to add the support to BizHawk. (I don't have the time to configure the environment etc)
Just like GB/C should. (I'm just saying)
Doesn't this rule give Game Gear an edge over SMS when a game is available on both platforms?
Just so it is known, even today's emulators do not emulate SMS well enough. For one thing, the startup state is known to be wildly incorrect. And for BIOS / post boot state, which should be chosen? Still it will be nice to move from old emulators and finally get some console verifications done with SMS runs. What would it take to quickly determine if Z80 R register is read by a game, as the easiest indicator of a console verifiable run? Static analysis? Analysis during gameplay?
This is really cool, I didn't realise that this was a big priority. It'll be interesting to see if the pause button can be used in any of these. Honestly about half of this list is on my list of possible future TASes so hopefully I can help to deal with this over time for any that are left over.
EDIT: I didn't aware about that bootup. I'll redo that Cyborg Hunter run to include this.
EDIT: Obsoleting dega movies quest deserves a topic.
