boot/main.asm

   1 bits    16
   2 org             0x7c00
   3
   4 start:          jmp loader
   5
   6
   7 TIMES 0Bh-$+start DB 0
   8
   9 bpbBytesPerSector:      DW 512
  10 bpbSectorsPerCluster:   DB 1
  11 bpbReservedSectors:     DW 1
  12 bpbNumberOfFATs:            DB 2
  13 bpbRootEntries:             DW 224
  14 bpbTotalSectors:            DW 2880
  15 bpbMedia:                   DB 0xF0
  16 bpbSectorsPerFAT:           DW 9
  17 bpbSectorsPerTrack:     DW 18
  18 bpbHeadsPerCylinder:    DW 2
  19 bpbHiddenSectors:           DD 0
  20 bpbTotalSectorsBig:     DD 0
  21 bsDriveNumber:          DB 0
  22 bsUnused:                   DB 0
  23 bsExtBootSignature:     DB 0x29
  24 bsSerialNumber:         DD 0xa0a1a2a3
  25 bsVolumeLabel:          DB "MOS FLOPPY "
  26 bsFileSystem:           DB "FAT12   "
  27
  28
  29 Print:
  30         pusha
  31         mov ah,0x0e
  32 .loop:
  33         mov al,[si]
  34         test al,al
  35         jz .end
  36         int 0x10
  37         inc si
  38         jmp .loop
  39 .end:
  40         popa
  41         ret
  42
  43
  44 LBAtoCHS:
  45         pusha
  46
  47         xor dx,dx
  48         div word [bpbSectorsPerTrack]
  49         inc dl
  50         mov byte [absSector],dl
  51
  52         xor dx,dx
  53         div word [bpbHeadsPerCylinder]
  54         mov byte [absHead],dl
  55
  56         mov byte [absTrack],al
  57         popa
  58         ret
  59
  60 ;CX Count
  61 ;ES:BX offset
  62 Read:
  63
  64 .read:
  65         call Reset
  66
  67         push ax
  68         push bx
  69         push cx
  70
  71         call LBAtoCHS
  72         mov ah,0x02
  73         xor dl,dl
  74         mov dh,[absHead]
  75         mov ch,[absTrack]
  76         mov cl,[absSector]
  77         mov al,1
  78
  79         int 0x13
  80         pop cx
  81         pop bx
  82         pop ax
  83         jc .read
  84         dec cx
  85         add bx,word [bpbBytesPerSector]
  86         inc ax
  87         test cx,cx
  88         jnz .read
  89         ret
  90
  91 Reset:
  92         pusha
  93
  94 .reset:
  95         mov ah,0
  96         mov dl,0
  97         int 0x13
  98         jc .reset
  99
 100         popa
 101         ret
 102
 103 ClusterLBA:
 104         sub ax,2
 105         xor cx,cx
 106         mov cl,byte [bpbSectorsPerCluster]
 107         mul cx
 108         add ax,word [data]
 109         ret
 110
 111 loader:
 112
 113         cli
 114         mov ax,cs
 115         mov ds,ax
 116         sti
 117
 118         mov ax,0x0003
 119         int 0x10
 120
 121         mov si,banner
 122         call Print
 123
 124         xor cx,cx
 125         xor dx,dx
 126         mov ax,0x0020
 127         mul word [bpbRootEntries]
 128         div word [bpbBytesPerSector]
 129         xchg ax,cx
 130
 131         mov al,[bpbNumberOfFATs]
 132         mul word [bpbSectorsPerFAT]
 133         add ax,[bpbReservedSectors]
 134
 135         mov word [data],ax
 136         add word [data],cx
 137
 138         push 0x0000
 139         pop es
 140         mov bx,0x7e00
 141
 142         call Read
 143
 144         mov cx,[bpbRootEntries]
 145         mov di,0x7e00
 146 .loop:
 147         push cx
 148         mov cx,11
 149         mov si,imageName
 150         push di
 151         rep cmpsb
 152         pop di
 153         je .ok
 154         pop cx
 155         add di,32
 156         loop .loop
 157         jmp .bad
 158
 159 .ok:
 160         mov si,ok
 161         call Print
 162         mov dx,word [di+0x1A]
 163         mov word [Cluster],dx
 164
 165         xor ax,ax
 166         mov al,[bpbNumberOfFATs]
 167         mul word [bpbSectorsPerFAT]
 168         xchg ax,cx
 169
 170         mov ax,[bpbReservedSectors]
 171
 172         push 0x0000
 173         pop es
 174         mov bx,0x7e00
 175
 176         call Read
 177
 178
 179         push 0x2000
 180         pop es
 181         xor bx,bx
 182         push bx
 183         push es
 184
 185 .load:
 186         pop es
 187         pop bx
 188
 189         mov ax,word [Cluster]
 190         call ClusterLBA
 191         mov cx,1
 192         call Read
 193         push bx
 194         push es
 195
 196         mov ax,word [Cluster]
 197         mov cx,ax
 198         mov dx,ax
 199         shr dx,0x0001
 200         add cx,dx
 201         push 0x0
 202         pop es
 203         mov bx,0x7e00
 204         add bx,cx
 205         mov dx,word [bx]
 206         test ax,0x0001
 207         jnz .odd
 208 .even:
 209         and dx,0000111111111111b
 210         jmp .done
 211 .odd:
 212         shr dx,0x0004
 213 .done:
 214         mov word [Cluster],dx
 215         cmp dx,0x0FF0
 216         jb .load
 217
 218
 219
 220         jmp 0x2000:0
 221         jmp .end
 222 .bad:
 223         mov si,bad
 224         call Print
 225 .end:
 226         cli
 227         hlt
 228
 229         absSector db 0
 230         absHead db 0
 231         absTrack db 0
 232         Cluster dw 0
 233         data dw 0
 234         imageName db "STAGE2  SYS"
 235         ok db "Stage2 was find...",13,10,0
 236         bad db "Stage2 dont find...",13,10,0
 237         banner db "Boot start...",13,10,0
 238         times 510 - ($-$$) db 0
 239         dw 0xAA55