bootrom.asm

   1         SECTION "a",HOME[$00]
   2
   3         LD SP,$fffe             ; $0000  Setup Stack
   4
   5         XOR A                   ; $0003  Zero the memory from $8000-$9FFF (VRAM)
   6         LD HL,$9fff             ; $0004
   7 Addr_0007:
   8         LD [HLD],A              ; $0007
   9         BIT 7,H         ; $0008
  10         JR NZ, Addr_0007        ; $000a
  11
  12         LD HL,$ff26             ; $000c  Setup Audio
  13         LD C,$11                ; $000f
  14         LD A,$80                ; $0011
  15         LD [HLD],A              ; $0013
  16         LD [C],A        ; $0014
  17         INC C                   ; $0015
  18         LD A,$f3                ; $0016
  19         LD [C],A        ; $0018
  20         LD [HLD],A              ; $0019
  21         LD A,$77                ; $001a
  22         LD [HLD],A              ; $001c
  23
  24         LD A,$fc                ; $001d  Setup BG palette
  25         LD [$FF47],A    ; $001f
  26
  27         LD DE,$0104             ; $0021  Convert and load logo data from cart into Video RAM
  28         LD HL,$8010             ; $0024
  29 Addr_0027:
  30         LD A,[DE]               ; $0027
  31         CALL a95                ; $0028
  32         CALL a96                ; $002b
  33         INC DE          ; $002e
  34         LD A,E          ; $002f
  35         CP $34          ; $0030
  36         JR NZ, Addr_0027        ; $0032
  37
  38         LD DE,$00d8             ; $0034  Load 8 additional bytes into Video RAM
  39         LD B,$08                ; $0037
  40 Addr_0039:
  41         LD A,[DE]               ; $0039
  42         INC DE          ; $003a
  43         LD [HLI],A              ; $003b
  44         INC HL          ; $003c
  45         DEC B                   ; $003d
  46         JR NZ, Addr_0039        ; $003e
  47
  48         LD A,$19                ; $0040  Setup background tilemap
  49         LD [$9910],A    ; $0042
  50         LD HL,$992f             ; $0045
  51 Addr_0048:
  52         LD C,$0c                ; $0048
  53 Addr_004A:
  54         DEC A                   ; $004a
  55         JR Z, Addr_0055 ; $004b
  56         LD [HLD],A              ; $004d
  57         DEC C                   ; $004e
  58         JR NZ, Addr_004A        ; $004f
  59         LD L,$0f                ; $0051
  60         JR Addr_0048    ; $0053
  61
  62         ; === Scroll logo on screen, and play logo sound===
  63
  64 Addr_0055:
  65         LD H,A          ; $0055  Initialize scroll count, H=0
  66         LD A,$64                ; $0056
  67         LD D,A          ; $0058  set loop count, D=$64
  68         LD [$FF42],A    ; $0059  Set vertical scroll register
  69         LD A,$91                ; $005b
  70         LD [$FF40],A    ; $005d  Turn on LCD, showing Background
  71         INC B                   ; $005f  Set B=1
  72 Addr_0060:
  73         LD E,$02                ; $0060
  74 Addr_0062:
  75         LD C,$0c                ; $0062
  76 Addr_0064:
  77         LD A,[$FF44]    ; $0064  wait for screen frame
  78         CP $90          ; $0066
  79         JR NZ, Addr_0064        ; $0068
  80         DEC C                   ; $006a
  81         JR NZ, Addr_0064        ; $006b
  82         DEC E                   ; $006d
  83         JR NZ, Addr_0062        ; $006e
  84
  85         LD C,$13                ; $0070
  86         INC H                   ; $0072  increment scroll count
  87         LD A,H          ; $0073
  88         LD E,$83                ; $0074
  89         CP $62          ; $0076  $62 counts in, play sound #1
  90         JR Z, Addr_0080 ; $0078
  91         LD E,$c1                ; $007a
  92         CP $64          ; $007c
  93         JR NZ, Addr_0086        ; $007e  $64 counts in, play sound #2
  94 Addr_0080:
  95         LD A,E          ; $0080  play sound
  96         LD [C],A        ; $0081
  97         INC C                   ; $0082
  98         LD A,$87                ; $0083
  99         LD [C],A        ; $0085
 100 Addr_0086:
 101         LD A,[$FF42]    ; $0086
 102         SUB B                   ; $0088
 103         LD [$FF42],A    ; $0089  scroll logo up if B=1
 104         DEC D                   ; $008b
 105         JR NZ, Addr_0060        ; $008c
 106
 107         DEC B                   ; $008e  set B=0 first time
 108         JR NZ, Addr_00E0        ; $008f    ... next time, cause jump to "Nintendo Logo check"
 109
 110         LD D,$20                ; $0091  use scrolling loop to pause
 111         JR Addr_0060    ; $0093
 112
 113         ; ==== Graphic routine ====
 114
 115 a95:    LD C,A          ; $0095  "Double up" all the bits of the graphics data
 116 a96:    LD B,$04                ; $0096     and store in Video RAM
 117 Addr_0098:
 118         PUSH BC         ; $0098
 119         RL C                    ; $0099
 120         RLA                     ; $009b
 121         POP BC          ; $009c
 122         RL C                    ; $009d
 123         RLA                     ; $009f
 124         DEC B                   ; $00a0
 125         JR NZ, Addr_0098        ; $00a1
 126         LD [HLI],A              ; $00a3
 127         INC HL          ; $00a4
 128         LD [HLI],A              ; $00a5
 129         INC HL          ; $00a6
 130         RET                     ; $00a7
 131
 132 Addr_00A8:
 133         ;Nintendo Logo
 134         DB $CE,$ED,$66,$66,$CC,$0D,$00,$0B,$03,$73,$00,$83,$00,$0C,$00,$0D
 135         DB $00,$08,$11,$1F,$88,$89,$00,$0E,$DC,$CC,$6E,$E6,$DD,$DD,$D9,$99
 136         DB $BB,$BB,$67,$63,$6E,$0E,$EC,$CC,$DD,$DC,$99,$9F,$BB,$B9,$33,$3E
 137
 138 Addr_00D8:
 139         ;More video data
 140         DB $3C,$42,$B9,$A5,$B9,$A5,$42,$3C
 141
 142         ; ===== Nintendo logo comparison routine =====
 143
 144 Addr_00E0:
 145         LD HL,$0104             ; $00e0 ; point HL to Nintendo logo in cart
 146         LD DE,$00a8             ; $00e3 ; point DE to Nintendo logo in DMG rom
 147
 148 Addr_00E6:
 149         LD A,[DE]               ; $00e6
 150         INC DE          ; $00e7
 151         CP [HL]         ; $00e8 ;compare logo data in cart to DMG rom
 152 .fuq    JR NZ,.fuq              ; $00e9 ;if not a match, lock up here
 153         INC HL          ; $00eb
 154         LD A,L          ; $00ec
 155         CP $34          ; $00ed ;do this for $30 bytes
 156         JR NZ, Addr_00E6        ; $00ef
 157
 158         LD B,$19                ; $00f1
 159         LD A,B          ; $00f3
 160 Addr_00F4:
 161         ADD [HL]                ; $00f4
 162         INC HL          ; $00f5
 163         DEC B                   ; $00f6
 164         JR NZ, Addr_00F4        ; $00f7
 165         ADD [HL]                ; $00f9
 166 .fuq:   JR NZ,.fuq              ; $00fa ; if $19 + bytes from $0134-$014D  don't add to $00
 167                                                 ;  ... lock up
 168
 169         LD A,$01                ; $00fc
 170         LD [$FF50],A    ; $00fe ;turn off DMG rom