Difference between revisions of "A78 Header Specification"
| Line 109: | Line 109: | ||
| − | == | + | == A78 Header Version Notes== |
| − | The current header version stands at | + | The current header version stands at 4, but not all flash carts and emulators are capable of reading v4 specific fields, nor do all games have them. |
| − | + | If game authors choose not to use/support any v4 features, then the header version should be kept at "3". If a v4 header is used, it's encouraged that v3 headers are also used where possible, to allow for maximal compatibility with emulators and flash carts. | |
| − | |||
| − | + | If an emulator or flash cart are v4 compatible, and they receive a rom with a v4 header, the v4 fields should take precedence over anything encoded in the equivalent v3 fields. | |
Revision as of 22:26, 20 January 2024
Contents
History and Purpose
The A78 header was originally created by Dan Boris, in tandem with his A7800 emulator. The header, which is added to the beginning of ROM images, serves to tell the emulator which hardware should be present for the game to run correctly.
The format has since been expanded to incorporate new hardware, and is now being used by multiple emulators and the Concerto 7800 flash cart.
A78 Header Fields
| 0000 | 04 | 41 | 54 | 41 | 52 | 49 | 37 | 38 | 30 | 30 | 00 | 00 | 00 | 00 | 00 | 00 | .ATARI7800...... |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0010 | 00 | 43 | 6f | 6d | 6d | 61 | 6e | 64 | 6f | 00 | 00 | 00 | 00 | 00 | 00 | 00 | .Commando....... |
| 0020 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | ................ |
| 0030 | 00 | 00 | 02 | 00 | 00 | 00 | 03 | 01 | 01 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | ................ |
| 0040 | 01 | 00 | 00 | 05 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | ................ |
| 0050 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | 00 | ................ |
| 0060 | 00 | 00 | 00 | 00 | 41 | 43 | 54 | 55 | 41 | 4c | 20 | 43 | 41 | 52 | 54 | 20 | ....ACTUAL CART |
| 0070 | 44 | 41 | 54 | 41 | 20 | 53 | 54 | 41 | 52 | 54 | 53 | 20 | 48 | 45 | 52 | 45 | DATA STARTS HERE |
| color | purpose | size | offset |
|---|---|---|---|
| header version | 1 byte | 0 / 0x00 | |
| ATARI7800 magic-text | 16 bytes | 1 / 0x01 | |
| cart title | 32 bytes | 17 / 0x11 | |
| rom size without header | 4 bytes | 49 / 0x31 | |
| cart type | 2 bytes | 53 / 0x35 | |
| controller 1 type | 1 byte | 55 / 0x37 | |
| controller 2 type | 1 byte | 56 / 0x38 | |
| TV type | 1 byte | 57 / 0x39 | |
| save device | 1 byte | 58 / 0x3A | |
| reserved | |||
| slot passthrough device | 1 byte | 63 / 0x3F | |
| v4+ mapper | 1 byte | 64 / 0x40 | |
| v4+ mapper options | 1 byte | 65 / 0x41 | |
| v4+ audio | 2 bytes | 66 / 0x42 | |
| v4+ interrupt | 2 bytes | 68 / 0x44 | |
| header end magic-text | 28 bytes | 100 / 0x64 |
cart type word details::
bit 0 = pokey at $4000 bit 1 = supergame bank switched bit 2 = supergame ram at $4000 bit 3 = rom at $4000 bit 4 = bank 6 at $4000 bit 5 = banked ram bit 6 = pokey at $450 bit 7 = mirror ram at $4000 bit 8 = activision banking bit 9 = absolute banking bit 10 = pokey at $440 bit 11 = ym2151 at $460/$461 bit 12 = souper bit 13 = banksets bit 14 = halt banked ram bit 15 = pokey@800
controller type byte details:
0 = none 1 = 7800 joystick 2 = lightgun 3 = paddle 4 = trakball 5 = 2600 joystick 6 = 2600 driving 7 = 2600 keypad 8 = ST mouse 9 = Amiga mouse 10 = AtariVox/SaveKey 11 = SNES2Atari
TV type details:
bit 0 = 0:NTSC, 1:PAL bit 1 = 0:component, 1:composite
save device details:
bit 0 = HSC bit 1 = SaveKey/AtariVox
expansion module:
bit 0 = XM
A78 Header Version Notes
The current header version stands at 4, but not all flash carts and emulators are capable of reading v4 specific fields, nor do all games have them.
If game authors choose not to use/support any v4 features, then the header version should be kept at "3". If a v4 header is used, it's encouraged that v3 headers are also used where possible, to allow for maximal compatibility with emulators and flash carts.
If an emulator or flash cart are v4 compatible, and they receive a rom with a v4 header, the v4 fields should take precedence over anything encoded in the equivalent v3 fields.
Adding Or Modifying an A78 Header on an Existing ROM
You can add or update an A78 header with the interactive command-line utility 7800header, which is distributed with 7800basic and the 7800AsmDevKit.
The utility displays the current header (or default header if the file is headerless) and you can set/unset hardware features with the displayed commands.
7800 A78 Header Info
embedded game name : Commando
rom size : 131072
cart format : Pokey@4000 SuperGame
controllers : 7800joy1 7800joy2
save peripheral : none
xm/xboard : not enabled
tv format : NTSC
Commands: "save" [name] Save the A78 file and exit.
"strip" [name] Save a headerless .BIN and exit.
"set [option]" Set one of the options.
"unset [option]" Unset one of the options.
"name game name" Set the game name in the header.
"exit" Exit the utility. Unsaved changes will be lost.
Options: rom@4000 bank6@4000 pokey@440 pokey@450 pokey@800 pokey@4000
ram@4000 mram@4000 hram@4000 ym2151@460 supergame bankram
absolute activision souper bankset tvpal tvntsc composite
7800joy1 7800joy2 lightgun1 lightgun2 paddle1 paddle2
tball1 tball2 2600joy1 2600joy2 driving1 driving2 keypad1
keypad2 stmouse1 stmouse2 amouse1 amouse2 hsc savekey xm
> exit
Adding an A78 Header to Source Code
To add an A78 header to your DASM source code, you can add or include the header at the start of your source, and adjust the fields to encode the hardware your game requires.
For the current a78 assembly-language header, see the a78 header github
