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Game Boy Boot ROM Disassembly
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| LD SP,$fffe ; $0000 Setup Stack | |
| XOR A ; $0003 Zero the memory from $8000-$9FFF (VRAM) | |
| LD HL,$9fff ; $0004 | |
| Addr_0007: | |
| LD (HL-),A ; $0007 | |
| BIT 7,H ; $0008 | |
| JR NZ, Addr_0007 ; $000a | |
| LD HL,$ff26 ; $000c Setup Audio | |
| LD C,$11 ; $000f | |
| LD A,$80 ; $0011 | |
| LD (HL-),A ; $0013 | |
| LD ($FF00+C),A ; $0014 | |
| INC C ; $0015 | |
| LD A,$f3 ; $0016 | |
| LD ($FF00+C),A ; $0018 | |
| LD (HL-),A ; $0019 | |
| LD A,$77 ; $001a | |
| LD (HL),A ; $001c | |
| LD A,$fc ; $001d Setup BG palette | |
| LD ($FF00+$47),A ; $001f | |
| LD DE,$0104 ; $0021 Convert and load logo data from cart into Video RAM | |
| LD HL,$8010 ; $0024 | |
| Addr_0027: | |
| LD A,(DE) ; $0027 | |
| CALL $0095 ; $0028 | |
| CALL $0096 ; $002b | |
| INC DE ; $002e | |
| LD A,E ; $002f | |
| CP $34 ; $0030 | |
| JR NZ, Addr_0027 ; $0032 | |
| LD DE,$00d8 ; $0034 Load 8 additional bytes into Video RAM | |
| LD B,$08 ; $0037 | |
| Addr_0039: | |
| LD A,(DE) ; $0039 | |
| INC DE ; $003a | |
| LD (HL+),A ; $003b | |
| INC HL ; $003c | |
| DEC B ; $003d | |
| JR NZ, Addr_0039 ; $003e | |
| LD A,$19 ; $0040 Setup background tilemap | |
| LD ($9910),A ; $0042 | |
| LD HL,$992f ; $0045 | |
| Addr_0048: | |
| LD C,$0c ; $0048 | |
| Addr_004A: | |
| DEC A ; $004a | |
| JR Z, Addr_0055 ; $004b | |
| LD (HL-),A ; $004d | |
| DEC C ; $004e | |
| JR NZ, Addr_004A ; $004f | |
| LD L,$0f ; $0051 | |
| JR Addr_0048 ; $0053 | |
| ; === Scroll logo on screen, and play logo sound=== | |
| Addr_0055: | |
| LD H,A ; $0055 Initialize scroll count, H=0 | |
| LD A,$64 ; $0056 | |
| LD D,A ; $0058 set loop count, D=$64 | |
| LD ($FF00+$42),A ; $0059 Set vertical scroll register | |
| LD A,$91 ; $005b | |
| LD ($FF00+$40),A ; $005d Turn on LCD, showing Background | |
| INC B ; $005f Set B=1 | |
| Addr_0060: | |
| LD E,$02 ; $0060 | |
| Addr_0062: | |
| LD C,$0c ; $0062 | |
| Addr_0064: | |
| LD A,($FF00+$44) ; $0064 wait for screen frame | |
| CP $90 ; $0066 | |
| JR NZ, Addr_0064 ; $0068 | |
| DEC C ; $006a | |
| JR NZ, Addr_0064 ; $006b | |
| DEC E ; $006d | |
| JR NZ, Addr_0062 ; $006e | |
| LD C,$13 ; $0070 | |
| INC H ; $0072 increment scroll count | |
| LD A,H ; $0073 | |
| LD E,$83 ; $0074 | |
| CP $62 ; $0076 $62 counts in, play sound #1 | |
| JR Z, Addr_0080 ; $0078 | |
| LD E,$c1 ; $007a | |
| CP $64 ; $007c | |
| JR NZ, Addr_0086 ; $007e $64 counts in, play sound #2 | |
| Addr_0080: | |
| LD A,E ; $0080 play sound | |
| LD ($FF00+C),A ; $0081 | |
| INC C ; $0082 | |
| LD A,$87 ; $0083 | |
| LD ($FF00+C),A ; $0085 | |
| Addr_0086: | |
| LD A,($FF00+$42) ; $0086 | |
| SUB B ; $0088 | |
| LD ($FF00+$42),A ; $0089 scroll logo up if B=1 | |
| DEC D ; $008b | |
| JR NZ, Addr_0060 ; $008c | |
| DEC B ; $008e set B=0 first time | |
| JR NZ, Addr_00E0 ; $008f ... next time, cause jump to "Nintendo Logo check" | |
| LD D,$20 ; $0091 use scrolling loop to pause | |
| JR Addr_0060 ; $0093 | |
| ; ==== Graphic routine ==== | |
| LD C,A ; $0095 "Double up" all the bits of the graphics data | |
| LD B,$04 ; $0096 and store in Video RAM | |
| Addr_0098: | |
| PUSH BC ; $0098 | |
| RL C ; $0099 | |
| RLA ; $009b | |
| POP BC ; $009c | |
| RL C ; $009d | |
| RLA ; $009f | |
| DEC B ; $00a0 | |
| JR NZ, Addr_0098 ; $00a1 | |
| LD (HL+),A ; $00a3 | |
| INC HL ; $00a4 | |
| LD (HL+),A ; $00a5 | |
| INC HL ; $00a6 | |
| RET ; $00a7 | |
| Addr_00A8: | |
| ;Nintendo Logo | |
| .DB $CE,$ED,$66,$66,$CC,$0D,$00,$0B,$03,$73,$00,$83,$00,$0C,$00,$0D | |
| .DB $00,$08,$11,$1F,$88,$89,$00,$0E,$DC,$CC,$6E,$E6,$DD,$DD,$D9,$99 | |
| .DB $BB,$BB,$67,$63,$6E,$0E,$EC,$CC,$DD,$DC,$99,$9F,$BB,$B9,$33,$3E | |
| Addr_00D8: | |
| ;More video data | |
| .DB $3C,$42,$B9,$A5,$B9,$A5,$42,$3C | |
| ; ===== Nintendo logo comparison routine ===== | |
| Addr_00E0: | |
| LD HL,$0104 ; $00e0 ; point HL to Nintendo logo in cart | |
| LD DE,$00a8 ; $00e3 ; point DE to Nintendo logo in DMG rom | |
| Addr_00E6: | |
| LD A,(DE) ; $00e6 | |
| INC DE ; $00e7 | |
| CP (HL) ; $00e8 ;compare logo data in cart to DMG rom | |
| JR NZ,$fe ; $00e9 ;if not a match, lock up here | |
| INC HL ; $00eb | |
| LD A,L ; $00ec | |
| CP $34 ; $00ed ;do this for $30 bytes | |
| JR NZ, Addr_00E6 ; $00ef | |
| LD B,$19 ; $00f1 | |
| LD A,B ; $00f3 | |
| Addr_00F4: | |
| ADD (HL) ; $00f4 | |
| INC HL ; $00f5 | |
| DEC B ; $00f6 | |
| JR NZ, Addr_00F4 ; $00f7 | |
| ADD (HL) ; $00f9 | |
| JR NZ,$fe ; $00fa ; if $19 + bytes from $0134-$014D don't add to $00 | |
| ; ... lock up | |
| LD A,$01 ; $00fc | |
| LD ($FF00+$50),A ; $00fe ;turn off DMG rom |
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Thanks! Here's 2 patches to get it to assemble with rgbds:
g'ah! And a second is needed to encode LDH properly!