ROMs question

[shilmover]

Does anyone know how I can modify an existing ROM?  I have a Ms Pac Man cab that I would like to make minor changes to the ROM.  I can test it in MAME, but I dont know how the ROMs are put together, configured, etc...

[Level42]

You need a hex editor for that.

There are plenty of free hex editors around.

For the Mac, there's 0xED (http://www.apple.com/downloads/macosx/development_tools/0xed.html) or
HexFiend (http://ridiculousfish.com/hexfiend/)

for the PC, I suggest HexEdit (http://www.physics.ohio-state.edu/~prewett/hexedit/)

Basically you load the ROM file, with the hex-editor you can see every byte of that rom file, usually both in hexadecimal and decimal value ("readable"). Now you can change at will, but you will have to know what you're doing. You may be able to find texts in the files (like (C)Namco) and change that. Or the names of the ghosts f.i.

However, some games may use checksums to see if the contents of the ROM is correct. If so, the checksum of the data won't be correct if you changed it. Depending on how the checksum is calculated and where it is stored you'd need to correct that. I'm not sure if the early games used any checksums but I think newer games might well do.

When you made your changes, save the file under a different name.
Make a new folder with the new rom files (and the old one's if there are no changes). Change the names back to what they were originally (the names that MAME expects) and try it in MAME. If it works, it should also work on the real board I guess. Than all you need to do is burn the modified files to a (new) EPROM.

[shilmover]

I got that far, but its not working...  for example, I tried to change PAC to CAP.

[Level42]

Then it must be the checksum thing I guess....


O wait, doesn't MAME check the ROMs ?

[Level42]

How about this:

http://home.kabelfoon.nl/~msilvius/down/pacname5.zip


(Found it here:
http://home.kabelfoon.nl/~msilvius/sillyarcade.htm

scroll down a bit to - PACMAN/MSPACMAN NAMES PATCHES -

Here's the readme file: http://home.kabelfoon.nl/~msilvius/down/readme5.txt

Whadayaknow, it's a fellow Dutchman who made this

Just reading the readme and it says you can even replace some graphics ! and I also was right about the checksum thing....

[Blanka]

Sta je ook op de Retro Computerdag 42?
From which game is Level 42 btw? From Chuckie Egg? Lemmings? Boulderdash?

[Ginsu Victim]

42 is the answer.

[Blanka]

Or are you referring to seventies hippie music?

[Ginsu Victim]

Uhhhhhhh.....no, but now you've got my interest.

It was a Douglas Adams reference.

[Level42]

Or are you referring to seventies hippie music?

Hippies ? 70's ?? No, it's 80's and jazz-funk !

One of their corniest pictures for sure.....

although this one is pretty corny too (Cambridge, UK, oct. 2006):



Go check out Level 42 live in Holland very soon:
http://www.level42.com/?page_id=91

O and yes it is very likely that I will be at the Retrocomputerdag with one of my cabs. I've been there since the last three years...

http://forum.arcadecontrols.com/index.php?topic=71621.0

Back on topic please

[Blanka]

Go check out Level 42 live in Holland very soon:
http://www.level42.com/?page_id=91

LOL, they their visitors are OLD now. It's all seated theaters 
It's a shame I know, that I don't remember them. I grew up with Europe and Van Halen, so they are about from the same time? When I saw that picture I posted, my only guess could be seventies. 

[Level42]

OK since Barry didn't report his results with the little program I suggested just yet, I will reply completely off-topic:

I HATE seated theaters for rock concerts !!!!!!!!!!  It's actually one of the reasons I still haven't got a ticket yet.....

Last gig I went to was 's Hertogenbosch (seated at a balcony for crying out loud.....) and it just doesn't do it for me.

Gigs should NOT be in seated venues.

The picture I put up was taken outside the Corn Exchange after the gig. It was seated (well they had put in those small fold-out chairs in there) but from the start to the end everybody was up on their legs.....thank God.....

When Mark King returned to the stages in the late 90's, he did (amongst others) a really small venue in London called the Jazz cafe. Absolutely no seats there and the stage was about 75 cm high. Was standing right in front of Mark (if I'd reached out, I could have played a couple of notes on his bass )  That, combined with a hardcore fan's set-list brought me the ultimate L42 gig, and I already told my wife then that it would never be like that again....I think that was around the turn of the millenium IIRC.

[shilmover]

WOW...  How Off Topic would this thread possible get?!?  It went past the topic by 30 years... backwards! 

<BackOnTopic>

That gave me a bit of info, but I still dont understand how the ROMs are put together so I can try them in MAME.  Anyone know of any docs to explain this?  Where does MAME get the game info when it start up?  How does it know which ROMs to load, in what order, what names?

Thanks

[RayB]

That gave me a bit of info, but I still dont understand how the ROMs are put together so I can try them in MAME.  Anyone know of any docs to explain this?  Where does MAME get the game info when it start up?  How does it know which ROMs to load, in what order, what names?

Thanks

Uhhhhh, it's not magic. MAME is (drum roll) programmed to "know".

[shilmover]

That gave me a bit of info, but I still dont understand how the ROMs are put together so I can try them in MAME.  Anyone know of any docs to explain this?  Where does MAME get the game info when it start up?  How does it know which ROMs to load, in what order, what names?

Thanks

Uhhhhh, it's not magic. MAME is (drum roll) programmed to "know".

LOL  I understand that, but if I wanted to create my own custom ROM in MAME...  How would i go about doing it?

[Level42]

Uhm, so did that little program I suggested didn't work ?

[shilmover]

nope.  ROMs are missing or I am doing something wrong.

[RayB]

LOL  I understand that, but if I wanted to create my own custom ROM in MAME...  How would i go about doing it?

Custom from the ground up? You'd have to first choose what chipsets you're going to base it on. For example, the combination of chips that make up the Ms Pac Man hardware. Then you'd have to learn how this hardware works, such as what memory banks graphics are stored, how the sprite system (if any) draws the graphics, where game code is located, what registers are used for input, what registers are used for sounds, etc. Then you'd need an assembly language editor to program some game logic (you could also program in straight machine language with a hex editor, but that's more difficult than using a compiler). You'd have to somehow disable or circumvent any part of the hardware that does anti-piracy checks (your code won't match that that custom chip will be looking for, therefore you need to change or stop it). etc, etc, etc.........