ROM header

Every WonderSwan ROM contains a header. It is stored at the end - final sixteen bytes - of the ROM image.

ROM header

Parts of this header are validated or otherwise used by the console's boot ROM - they are marked in bold.

Header contents

Offset	Length	Contents
$0	5	Far jump instruction: 0xEA, offset, segment.
$5	1	Maintenance
$6	1	Developer/Publisher ID
$7	1	Color
$8	1	Game ID (binary-coded decimal)
$9	1	Game version? / Safe mode
$A	1	ROM size
$B	1	Save type/size
$C	1	Flags
$D	1	Mapper type
$E	2	Checksum (sum of all ROM bytes excluding the checksum)

$5 - Maintenance

7  bit  0
---- ----
s... 0000
|    ||||
|    ++++- Must be zero; otherwise the console will prohibit execution.
|          Purpose unknown.
+--------- (Color) Splash bypass: 0 = Disable, 1 = Enable.
           Bypasses the custom boot splash stored in the console's
           internal EEPROM; presumably used for bricked console recovery.

$6 - Developer/Publisher ID

Known official developer/publisher IDs

ID	Publisher
$01	Bandai
$02	Taito
$03	?
$04	Koei
$05	Data East
$06	Asmik Ace
$07	Media Entertainment
$08	Nichibutsu
$0A	Coconuts Japan
$0B	Sammy
$0C	Sunsoft
$0D	?
$0E	Banpresto
$10	Jaleco
$11	Imagineer
$12	Konami
$16	Kobunsha
$17	Bottom Up
$18	?
$19	Sunrise
$1A	Cyber Front
$1B	Megahouse
$1D	Interbec
$1E	?
$1F	?
$20	Athena
$21	KID
$22	?
$23	?
$24	Omega Micott
$25	?
$26	?
$27	?
$28	Squaresoft
$2A	?
$2B	?
$2D	Namco
$2E	?
$2F	?
$31	?
$32	?
$33	?
$36	?

Note that IDs $00 and $01 are used across a variety of commercial games. Homebrew is known to use arbitrary values in this field.

$7 - Color

7  bit  0
---- ----
???? ???c
        |
        +- 0 = Monochrome only, 1 = Supports Color mode.

$9 - Game version? / Safe mode

7  bit  0
---- ----
pvvv vvvv
|||| ||||
|+++ ++++- Game version?
+--------- Internal EEPROM write protect: 0 = Enable, 1 = Disable.
           This prohibits writing to the internal EEPROM for addresses
           0x60 and above (user settings, custom splash screen).
           Games are expected to enable write protection; however, the
           WonderWitch is factory configured with it disabled.

$A - ROM size

Unofficial ROM size values are marked in italic.

ROM size values

ID	Size
$00	1 Mbit (128 KiB)
$01	2 Mbit (256 KiB)
$02	4 Mbit (512 KiB)
$03	8 Mbit (1 MiB)
$04	16 Mbit (2 MiB)
$05	24 Mbit (3 MiB)
$06	32 Mbit (4 MiB)
$07	48 Mbit (6 MiB)
$08	64 Mbit (8 MiB)
$09	128 Mbit (16 MiB)
$0A	256 Mbit (32 MiB)
$0B	512 Mbit (64 MiB)

$B - Save type/size

Save type values

ID	Type	Size
$00	None
$01	SRAM	64 Kbit (8 KiB)
$02		256 Kbit (32 KiB)
$03		1 Mbit (128 KiB)
$04		2 Mbit (256 KiB)
$05		4 Mbit (512 KiB)
$10	EEPROM	1 Kbit (128 B)
$20		16 Kbit (2 KiB)
$50		8 Kbit (1 KiB)

$C - Flags

7  bit  0
---- ----
???? ?SBv
      |||
      ||+- Starting screen orientation: 0 = Horizontal, 1 = Vertical.
      ||   Controls the splash screen's orientation.
      |+-- ROM bus width: 0 = 16-bit, 1 = 8-bit.
      +--- ROM access time: 0 = 3 CPU cycles, 1 = 1 CPU cycle.

$D - Mapper type

Known mapper types

ID	Mapper
$00	Bandai 2001
$01	Bandai 2003
$02	KARNAK (Pocket Challenge V2)