2gen header

Sik · Post by **Sik** » Fri May 02, 2008 8:47 pm

Well, let's start with the 2gen thingy. Just so you know, 2gen would be the second generation of Mega Drive games, probably most of it homebrew

I want to remark that Ninja Fight isn't what I would like from 2gen, it's too simple, I want 2gen to prove that the Mega Drive can do wonders with the hardware it has >_> I may start making another game that would deserve the 2gen qualification, and you'll see what I mean.

By the way, now let's start discussing about the format of a new Mega Drive header, OK? Probably a lot of you don't find enough the information you can put in the standard header, so let's make a new one

What kind of information? Well, things like what kind of memory is being used if you have SRAM, mappers or even if you have several kind of memories (like normal RAM and SRAM in the same cartridge, or mirrored RAM that is accessed differently, like the RAM in the Sega CD that can be accessed both as a bitmap or as a tilemap, depending from which address it's accessed (it's just a line swap)). Once we're done, I'll put the official specifications for this new header in my page, OK?

Some notes:

The new header must be compatible with the old one, that is, the old fields should remain, and must be filled with valid data (this doesn't imply we can't extend the functionality of those fields).
Sega won't update the old header at this point so let's assume that the reserved fields are free for the new header to use.
The new header doesn't need to have the same size as the old one, so feel free to add new fields after the original 256 bytes. This may clash with the 32x, but we would probably make special code to override the lock-up of the 32x BIOS.
There must be an easy way to identify the old header from the new one. The best way to do it probably is using a reserved field to contain certain value if it's the new header, or modifying the magic to say something like "SEGA 2GEN" instead of "SEGA MEGA DRIVE" or "SEGA GENESIS".
If I make a 2gen BIOS, it'll be able to recognise the 2gen header (even if just to retrieve info if the user wants to know). It would be cool if, for example, Regen was compatible with it and could retrieve info from it.

Having said all this, let's start. Please don't go and make an entire new header and post it, instead suggest what kind of stuff you would want to see and we'll finish up making the new header format between all of us, OK?

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat May 03, 2008 5:54 am

Here's some stupid stuff in my Work in Progress MD/Genny programming guide for dumbasses :

Code: Select all

ROM header follows the IVT. Typical header consists of :

1)  Name of the system
2)  Copyright
3)  Local name
4)  International name
5)  Type, Game ID and Version
6)  Checksum
7)  Supported I/O devices
8)  ROM size
9)  RAM size
10) External memory type and size
11) Modem info
12) Whatever field
13) Regions

* Name of the system is 16 bytes long and is usually "SEGA MEGA DRIVE " or
  "SEGA GENESIS    ". "SEGA" must be included as the TMSS looks for it and
  will not run the program if it isn't there.

* Copyright is 16 bytes long and can be anything. It is usually "(C)", four
  letter company (or code) and date. Typical copyright: "(C)SEGA 1991.SEP".

* Both Local and International name are 48 bytes long. Local name is more
  known as domestic name, but I like local more. Usually in manufacturer's
  native language. I'm Estonian and I use an Estonian name there.
  International name should be in English, so most of the people could
  understand it. For example if I put "See on testimis programm" there, only
  a tiny fraction of Earth's population will understand it. If I put there
  "This is a testing program" you know exactly what it means. Emulators
  display the interntional name.

* Type, ID and version field is 16 bytes long and it shows info about the
  ROM image. Type shows what kind of program it is. All the types I know :

  "GM" - Game
  "DM" - Demo
  "DS" - Developement System
  "OS" - Operating System?, TMSS in MD
  "AI" - Educational
  "PX" - Pictures

  ID is usually used in commercial games to make catalogging games easier ?
  In my programs, ID shows the order of starting to write the program.
  During the writing of this document, I've made 28 programs for MD.

  Version is usually 2 bytes long, ordinary HEX number i.e "1A".

* Checksum is a 2 byte value which is used to determine the integrity of
  the ROM on a cartidge (low quality ROMs tend to bit-rot). If the checksum
  is incorrect the game usually displays red screen or a message. You
  could say, that it is meant to prevent hacking, but this doesn't stop
  any hacker.

* Supported I/O devices field is 16 bytes long. Device codes I know :

  J - 3-button control pad
  6 - 6-button control pad
  0 - Master System control pad
  K - Keyboard
  P - Printer (never seen such device for MD)
  B - Control ball
  F - Floppy Disk Drive (never seen such device for MD)
  L - Activator
  4 - Team play (multi tap)
  R - RS-232C serial port
  T - Tablet (What is this?)
  V - Paddle controller
  C - CD-ROM
  M - Mouse

  I've seen D but I have no clue what it is. It may relate to Developement.
  Also I've seen O in an unreleased game (that was in GEMS package)

* ROM size, consists of 2 LONGs. Can be upto 4MB ($000000 to $3FFFFF) or
  above if bank switching techniques are used.

* RAM size, 2 LONGs too. Why do you need it ? Any MD has 64KB of RAM. I've
  seen only $FF0000 and $FFFFFF. MD RAM is mirrored (repeated) form $E00000 
  to $FFFFFF. I believe, that MD was planned to have more than 64KB or RAM
  but later the idea was dropped to cut cost (MDs were pretty expensive).

* External memory type and size shows if it is used in your cartridge. You
  and have several kinds of memories. Usually RAM is used, but there are
  games that use EEPROM. This memory is usually put into cartidges to save
  your progress, configurations, high-scores etc. Static RAMs are used for
  that, but there are cartridges that use EEPROMs. Usage of 5V Flash is
  possible too now, but Flash is not so infinite like SRAM or EEPROM, and
  proposes some difficulties when you are going to program one. "RA" is
  used to show that memory is used (there are games that use extra memory,
  but don't show that they do). Next byte shows how this memory is connected
  and its purpose.

  This byte looks like this (in binary): 1A1BC000

  A  - 1  - Back-up
       0  - Some other purpose
  BC - 11 - ODD addresses (!WE on RAM connects to !LDSW)
       10 - EVEN addresses (!WE on RAM connects to !UDSW)
       01 - Both EVEN and ODD addresses, BYTE/WORD access - my expansion
       00 - Both EVEN and ODD addresses, WORD access

  Next byte shows what kind of RAM is is. I know only 3 types :

  $20 - SRAM
  $40 - I2C EEPROM (24Cxx)
  $80 - MicroWire EEPROM (93Cxx) - my expansion

  2 LONGs follow, first is $200000 and other should not exceed $20FFFF.
  Most emulators emulate only 64KB of SRAM, but they should emulate up to
  2MB like Genecyst. 2MB is the maximum amount you can get if you use
  "standard" SRAM accessing method. EEPROMs are almost not emulated, during
  the writing of this document, only Kega Fusion supported few of many 
  EEPROM accessing methods.

* Modem info is 10 bytes long and it shows info about the modem if used.
  You can put anything there if you like but IF you do support a modem use
  this formatting: "MO", company code (4 bytes) modem number (?), ".",
  modem version. All in ASCII. Example :

 DC.B   "MO", "TmEE", "00.0" 

* Whatever field can contain anything you like. Sonic & Knuckles cartridge
  has there info about extra ROM (not SRAM/EEPROM), I always put there some
  random thoughts, many put nothing.

* Regions is 16 bytes long field like I/O device field. This contains info
  about regions that your program can run in. All region codes I know:

  E - Europe, Estonia(hehe)
  U - USA
  J - Japan
  F - France
  B - Brazil
  4 - Brazil*
  8 - Hong Kong
  A - Asia
  C -

  * Also seen it on US game

  It is told that all other codes than E, U, J should be accepted as E. It
  is partially true, because AFAIK, most of the countries that are not Japan
  or USA use PAL or SECAM television standard.


Header (in DOS encoding) I used in an early version of "CA the meowian" :

 DC.B   "SEGA MEGA DRIVE "     ; System name
 DC.B   "(C)TmEE co. 2007"     ; Copyright [2007.FEB -> 200*.***]
 DC.B   "Mj„ulane CA - kuradi kasutu alfa !!!            "   ; Name (local)
 DC.B   "CA the meowian - damn useless alpha !!!         "   ; Name (int.)
 DC.B   "GM T-000014-00"       ; Type, mfgr.ID-Serial-Version
 DC.W   $0000                  ; Checksum
 DC.B   "J               "     ; I/O support
 DC.L   $00000000, $0002FFFF   ; ROM start->end
 DC.L   $00FF0000, $00FFFFFF   ; RAM start->end, why ???
 DC.B   "RA", %11111000, $20   ; External RAM info
 DC.L   $00200001, $002001FF   ; External RAM start->end
 DC.B   "No modem... "         ; Modem shit      
 DC.B   "(8<| - Dark side of the Force rules !!! "   ; Whatever
 DC.B   "E  like Estonia "     ; Regions

TascoDLX · Post by **TascoDLX** » Sat May 03, 2008 9:08 am

TmEE co.(TM) wrote:Regions is 16 bytes long field like I/O device field. This contains info
about regions that your program can run in. All region codes I know:

E - Europe, Estonia(hehe)
U - USA
J - Japan
F - France
B - Brazil
4 - Brazil*
8 - Hong Kong
A - Asia
C -

* Also seen it on US game

It is told that all other codes than E, U, J should be accepted as E. It
is partially true, because AFAIK, most of the countries that are not Japan
or USA use PAL or SECAM television standard.

This can get confusing.

Later games use a unique system for the region. A single letter is used representing a hexadecimal digit (4 bits) with each bit representing a different console type (NTSC/PAL, domestic/overseas) as determined from the console's version register. If a bit is set, the game is OK for that console type.

bit 3 : PAL overseas
bit 2 : NTSC overseas
bit 1 : PAL domestic
bit 0 : NTSC domestic

For example, code 'F' (1111) is OK for all consoles (any region), code 'A' (1010) is PAL only, code '4' (0100) is used for games exclusive to the US [NTSC overseas], and so on....

I don't know exactly when Sega started using this system. The earliest game I see that uses it is (copyright) May 1995, though I've only looked at a few.

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat May 03, 2008 11:17 am

I didn't know about that bit stuff... in my stuff it doesn't matter what is in header... its just there for anyone's reading pleasure.

Sik · Post by **Sik** » Sat May 03, 2008 4:05 pm

If you have GenesisSoftwareManual.pdf, that new header system is documented there, I think as one as the memos (I always mix memos and addenums, but I think this one is a memo

). Go and check. Anyways once I made a poll and people liked more the old system, including myself, so I think I'm gonna stick with it.

The ROM type "OS" is used by BIOSes (both Mega Drive and Mega CD). I know this because I found this type while disassembling the MD BIOS to research how does it work

Then I found it on the Mega CD BIOS headers. MD BIOS ID is "OS 00000000-00" (no kidding). If you make a BIOS, you should set it to be "OS".

We should make some kind of comitee or something like that to give out our own ROM serial codes

From the I/O device list, you're missing "A", which is the analog joystick supported by After Burner 2. I also recall having seen "D", through I don't remember where (Imma check later). I assume the tablet is the one from the SMS. Take into mind that most of the devices in the list are just placeholders for devices (such as the keyboard, the floppy disk and the printer) Sega may make in the future (since the SMS had some weird devices). Also, notice that if you look into $A10001, bit 4 will suppodsely tell you if there's a floppy disk drive attached. It never was used with that purpose, however when the Mega CD appeared it told you if it was plugged, so I would assume it actually tells you if any kind of drive is installed.

About the external RAM field, I never knew the fourth byte determined the form of RAM to be used. Neither official docs nor any other doc mention it, and I thought it was $20 because that's the ASCII code for a space o_o' (maybe originally that was the case).

There are four official country codes: 'J', 0, 'U' and 'E', representing NTSC domestic, PAL domestic, NTSC overseas and PAL overseas. The main reason about why all country codes different to those worked as 'E' is because it's last in the list, and the subroutine that checked for them just checked each country by hand. If it wasn't either 'J', 0 or 'U', then it assumed it was 'E' because it was the remaining one in the list. That's from where it comes, but it all really depends on how the game was coded.

Back on the 2gen header, I think that putting "SEGA 2GEN" in the magic will be better, through trying to access the "2GEN" part as a dword will be a bit hard (as it isn't even aligned). If you add a space, this leaves us with space for 6 characters, and I was thinking we could use that space to identify the game type like "SEGA 2GEN GAME ", which would be way better than the two characters the ROM serial no. field gives us. The 2gen BIOS will have "SEGA 2GEN BIOS " as a magic, so if you want to check if it's installed, you could temporarily bank switch to it and check if the dword at $110 to see if it's "BIOS"

What do you think about it?

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat May 03, 2008 4:27 pm

Sik wrote:If you have GenesisSoftwareManual.pdf, that new header system is documented there, I think as one as the memos (I always mix memos and addenums, but I think this one is a memo ). Go and check. Anyways once I made a poll and people liked more the old system, including myself, so I think I'm gonna stick with it.

I must have skipped that part...

The ROM type "OS" is used by BIOSes (both Mega Drive and Mega CD). I know this because I found this type while disassembling the MD BIOS to research how does it work Then I found it on the Mega CD BIOS headers. MD BIOS ID is "OS 00000000-00" (no kidding). If you make a BIOS, you should set it to be "OS".

OK, good to know... but what a real Operating System ROM should have then ?

We should make some kind of comitee or something like that to give out our own ROM serial codes

I'm gonna stick with my way... its too late to break it... 30 ROMs already...

From the I/O device list, you're missing "A", which is the analog joystick supported by After Burner 2. I also recall having seen "D", through I don't remember where (Imma check later). I assume the tablet is the one from the SMS. Take into mind that most of the devices in the list are just placeholders for devices (such as the keyboard, the floppy disk and the printer) Sega may make in the future (since the SMS had some weird devices). Also, notice that if you look into $A10001, bit 4 will suppodsely tell you if there's a floppy disk drive attached. It never was used with that purpose, however when the Mega CD appeared it told you if it was plugged, so I would assume it actually tells you if any kind of drive is installed.

I didn't know about the A used for Analog in AfterBurner2... I wanted to have A for my device

And that FDD bit can be changed my shorting pin B2 on MD expansion port.

About the external RAM field, I never knew the fourth byte determined the form of RAM to be used. Neither official docs nor any other doc mention it, and I thought it was $20 because that's the ASCII code for a space o_o' (maybe originally that was the case).

That extra byte is documented... I just added MicroWire EEPROM to it... since my game will use it...

Back on the 2gen header, I think that putting "SEGA 2GEN" in the magic will be better, through trying to access the "2GEN" part as a dword will be a bit hard (as it isn't even aligned). If you add a space, this leaves us with space for 6 characters, and I was thinking we could use that space to identify the game type like "SEGA 2GEN GAME ", which would be way better than the two characters the ROM serial no. field gives us. The 2gen BIOS will have "SEGA 2GEN BIOS " as a magic, so if you want to check if it's installed, you could temporarily bank switch to it and check if the dword at $110 to see if it's "BIOS"

What do you think about it?

What's the point of this 2GEN ?

Sik · Post by **Sik** » Sat May 03, 2008 5:04 pm

TmEE co.(TM) wrote:
Sik wrote:If you have GenesisSoftwareManual.pdf, that new header system is documented there, I think as one as the memos (I always mix memos and addenums, but I think this one is a memo ). Go and check. Anyways once I made a poll and people liked more the old system, including myself, so I think I'm gonna stick with it.
I must have skipped that part...

Genesis Technical Bulletin #31. Yup, it's there

TmEE co.(TM) wrote:
The ROM type "OS" is used by BIOSes (both Mega Drive and Mega CD). I know this because I found this type while disassembling the MD BIOS to research how does it work Then I found it on the Mega CD BIOS headers. MD BIOS ID is "OS 00000000-00" (no kidding). If you make a BIOS, you should set it to be "OS".
OK, good to know... but what a real Operating System ROM should have then ?

Mmmmmmh... "OS"?

I guess the BIOS could be considered sorta kind of mini-OS or something.

TmEE co.(TM) wrote:
We should make some kind of comitee or something like that to give out our own ROM serial codes
I'm gonna stick with my way... its too late to break it... 30 ROMs already...

It's just to prevent serial number clashing. I think Sega had like three different patterns for giving them

TmEE co.(TM) wrote:
From the I/O device list, you're missing "A", which is the analog joystick supported by After Burner 2. I also recall having seen "D", through I don't remember where (Imma check later). I assume the tablet is the one from the SMS. Take into mind that most of the devices in the list are just placeholders for devices (such as the keyboard, the floppy disk and the printer) Sega may make in the future (since the SMS had some weird devices). Also, notice that if you look into $A10001, bit 4 will suppodsely tell you if there's a floppy disk drive attached. It never was used with that purpose, however when the Mega CD appeared it told you if it was plugged, so I would assume it actually tells you if any kind of drive is installed.
I didn't know about the A used for Analog in AfterBurner2... I wanted to have A for my device
[img]

That analog joystick only works with the After Burner series that can run on the MD (AB2, AB3, AB1 32x)

TmEE co.(TM) wrote:
About the external RAM field, I never knew the fourth byte determined the form of RAM to be used. Neither official docs nor any other doc mention it, and I thought it was $20 because that's the ASCII code for a space o_o' (maybe originally that was the case).
That extra byte is documented... I just added MicroWire EEPROM to it... since my game will use it...

Where is it?

TmEE co.(TM) wrote:
Back on the 2gen header, I think that putting "SEGA 2GEN" in the magic will be better, through trying to access the "2GEN" part as a dword will be a bit hard (as it isn't even aligned). If you add a space, this leaves us with space for 6 characters, and I was thinking we could use that space to identify the game type like "SEGA 2GEN GAME ", which would be way better than the two characters the ROM serial no. field gives us. The 2gen BIOS will have "SEGA 2GEN BIOS " as a magic, so if you want to check if it's installed, you could temporarily bank switch to it and check if the dword at $110 to see if it's "BIOS"

What do you think about it?
What's the point of this 2GEN ?

Why do you always have to question everything I want to do? >_>

Anyways, the idea for 2gen is that it would be the second generation of Mega Drive games. It'll start as homebrew, through somebody may finish up making commercial games eventually (and the MD being sold again?). No idea how far it'll reach in that sense

Anyways, I want the main characterisc for 2gen to prove that the MD can be a great console, both gameplay and hardwarewise (which is why I don't consider Ninja Fight to be 2gen, man, it'll suck in both terms

). That's all about it

Shiru · Post by **Shiru** » Sun May 04, 2008 2:43 am

Sik wrote:Anyways, I want the main characterisc for 2gen to prove that the MD can be a great console, both gameplay and hardwarewise

There already was many such games, with great gameplay and tech. Because of them we all is here. And it's highly unlikely that somebody of homebrew developers can make something even comparable with these old games.

Sik · Post by **Sik** » Sun May 04, 2008 3:26 am

There are several homebrew games that look and perform way better than commercial games

Like it or not most games don't make very good use of hardware. Even Sonic games, which look good enough to make you forget that the MD is running on two tiled scrolls and sprites, don't make the best use of the hardware. Not bad, but we could push it to do even more. Only very few games such as Gunstar Heroes, Ranger X or Vectorman do really cool tricks with the hardware.

I was already thinking in something that would do. Imma start the ROM tomorrow, if not after finishing with this post. And yes, this is the very same ROM for which I asked the mode-4 support in Regen, through I think that after all I'm going to drop it and use VLBitmap2Scroll (the bitmap needed wouldn't be too big to drop the framerate in that section).

Anyways, it's all on us. Of course, if you don't put effort, you won't get a good game. And you don't need really very complex things to get cool effects, trust me, learn well what capabilities does the hardware give you and everything will be a lot easier to make cool things. Nothing is impossible

Shiru · Post by **Shiru** » Sun May 04, 2008 3:52 am

Sik wrote:There are several homebrew games that look and perform way better than commercial games :P

So, name them.

Sik wrote:Only very few games such as Gunstar Heroes, Ranger X or Vectorman do really cool tricks with the hardware.

Batman and Robin
Contra Hard Corps
Kawasaki Superbike
Red Zone
Toy Story
etc

So, there was not so few games which good tech. And you also speaking about good gameplay, which much more games have. Even mentioned Sonic games.

And now look to staff rolls of these games and think that all those people was skilled professionals which worked hard on full-time paid work for year or so for one game.

Sik wrote:..trust me..

You often use these words. For me, they means that you don't know how to prove your statements, and this only reduces trust. I don't have to trust or don't trust you because you say so, I have enough of my own knowledge and experience to decide if you say right things or not.

Sik · Post by **Sik** » Sun May 04, 2008 4:46 am

What you make me understand is that you think that nobody will be able to do wonders with the MD again, right? OK, now explain me why not. And please don't put the same excuse again:

Shiru wrote:And now look to staff rolls of these games and think that all those people was skilled professionals which worked hard on full-time paid work for year or so for one game.

The skill has nothing to do with being professional or not. There are lots of excellent programmers out there that never studied it as a career, otherwise why are so many free and even open source programs available? Most of them definitely weren't made by people who aren't programming proffesionals. And about time, effectively those games would take longer to develop, but that doesn't mean they can't be done.

Shiru · Post by **Shiru** » Sun May 04, 2008 6:18 am

First, where is list of 'homebrew games that look and perform way better than commercial games'?

Sik wrote:What you make me understand is that you think that nobody will be able to do wonders with the MD again, right?

I said that I said: it's highly unlikely that homebrew developers can make something comparable with old commercical games, not speaking about something superior. Not impossible, but probability is quite low.

And nobody did any wonders. There was some games which used SMD potential well, and some which not.

Sik wrote:OK, now explain me why not.

Homebrew developers does not have experience, resources and motivation which pro developers had.

Currently there is very few finished SMD homebrew game projects of any quality, though platform available for homebrew developement for about ten years. And there is no finished homebrew games which can be compared with old commercial titles. I explained why we has this situation. Can you explain it otherwise?

Sik wrote:There are lots of excellent programmers..

Code is very small part of game project. You can't make good game with only code. Game project is design, planning, management, art, and only then some code. Most of homebrew developers even don't know what design, planning and management is, and why it's important. Thus there (on any platform) is much less finished game projects than software ones (tools etc), and many of finished game projects has very low quality.

Eke · Post by **Eke** » Sun May 04, 2008 8:46 am

I totally agree with Shiru. And also in term of game originality, I've yet to find a homebrew that is not inspirated by an original production and have this "professional" look, even if I have lot of respect for people doing their own "artisanal" games because it is great to keep old systems alive and not so easy when you don't have access to official devkit.
There were tons of games on the genesis that brought surprising new gameplay ideas, or using all hardware features to provide great graphics&musics, but you can feel that a lot of money was put into production to achieve this...

On the contrary, it's also true that a lot of games were cheap and seemed to limit themselves to the strict minimum, without really much more ambition than grabbing some money from gamers

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sun May 04, 2008 3:52 pm

I'd like to see the list of GOOD homebrew games for MD...

I have over 130 MD homebrew ROMs, which of games are maybe 10, and which of good are none (though Glass Breaker MD can be considered good... but I made it so my opinion is not objective)... what Sik is making seems promising, but its too early to tell if it will be good or not.

I have a huge project smoking... which will end up commercial, and will be on par with some nice MD shooters...

Sik · Post by **Sik** » Sun May 04, 2008 7:24 pm

When I was talking about homebrew having better quality than commercial games, I wasn't talking just about the Mega Drive. This is specially true these days, where developers keep launching poor games to see if some give them enough money.

But c'mon, what I see is that it seems like you lost the hope. Do you know what? Then you can't be here. Sorry, but if you want to develop for a platform such as the Mega Drive that isn't supported anymore, you need hope, because nobody will try to help you except yourselves, and in fact people will try to convince you that you should stop being childish and go to develop for a platform more commonly used today (you don't know how many times I was asked to stop messing up with the Mega Drive).

In short: if you want to make games for a platform such as the Mega Drive, you need hope, because otherwise you won't reach far. And you seem to have started losing it... >_>