Custom Genesis BIOS

This BIOS displays a simple message and an icon before booting the game, ala DS (the official games are unaffected)
The icon, description, pallet, even the font can be customized

Examples:

My sonic hack

(Temporary icon)

Test ROM


This requires a special header, which I'll put the it in my next post Below

Download:
BIOS
Test ROM ("Hello World!")

The BIOS checks for the string "GF64" at $C0
and starting from $D0, it grabs the full [LONG] locations of the pallet, font, icon and description (in this order)

From the "Hello World!" ROM:

Code (ASM):

1.         dc.l $FFFE00,Entrypoint,ErrorTrap,ErrorTrap
2.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
3.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
4.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
5.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
6.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
7.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
8.         dc.l HBlank,ErrorTrap,VBlank,ErrorTrap
9.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
10.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
11.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
12.         dc.l ErrorTrap,ErrorTrap,ErrorTrap,ErrorTrap
13.  
14.         dc.b "GF64            "
15.         dc.l BIOS_Pal,BIOS_art_txt,BIOS_art_icon,BIOS_txt
16.         dc.b "                " ; Reserved for something else...
17.         dc.b "                "
18.  
19.         dc.b "SEGA Genesis    "
20.         dc.b "(C)GF64 2010.???"     ;the board replaced ( C ) [without spaces] to (C)
21.         dc.b "GF64",$27,"s SAMPLE PROGRAM                           "
22.         dc.b "GF64",$27,"s SAMPLE PROGRAM                           "
23.         dc.b "GM MK-1337 -00"
24.         dc.w 0
25.         dc.b "J               "
26.         dc.l 0
27.         dc.l 0
28.         dc.l $FF0000
29.         dc.l $FFFFFF
30.         dc.l $20202020
31.         dc.l $20202020
32.         dc.l $20202020
33.         dc.b "                                                    "
34.         dc.b "JUE             "
35.  
36. ; Note: the data can be placed anywere in the ROM
37. BIOS_Pal:   incbin  "BIOS\pal.bin"
38.         even
39.  
40. BIOS_Art_Txt:   incbin  "BIOS\art.bin"  ;Font
41.         even
42.  
43. BIOS_Art_Icon:  incbin  "BIOS\icon.bin" ;Icon 32x32
44.         even
45.  
46. ; "}" = space
47. ; "{" = end-of-text
48.  
49. BIOS_Txt:   dc.b    "Sample Program","}"
50.         dc.b    "}"
51.         dc.b    "}"
52.         dc.b    "\#_day/\#_month/2011","{"
53.         even

 

^ That's the reason why I used $C0

True. I only made this for testing purposes... but it looked good to show it here, oh well.