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Game Boy Boot ROM Disassembly
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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