com32/gfxboot/realmode_callback.asm

   1                 bits 16
   2
   3                 section .text
   4
   5                 ; must be filled in
   6 f_buf_size      dw 0
   7 f_buf_seg       dw 0
   8
   9
  10 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  11 gfx_cb:
  12                 push cs
  13                 pop ds
  14
  15                 cmp al,cb_len
  16                 jae gfx_cb_80
  17
  18                 movzx bx,al
  19                 add bx,bx
  20                 call word [bx+cb_table]
  21                 jmp gfx_cb_90
  22
  23 gfx_cb_80:
  24                 mov al,0ffh
  25 gfx_cb_90:
  26                 retf
  27
  28
  29 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  30 ; Return status info.
  31 ;
  32 ; return:
  33 ;  edx          filename buffer (64 bytes)
  34 ;
  35 cb_status:
  36                 mov edx,cs
  37                 shl edx,4
  38                 add edx,f_name
  39                 xor al,al
  40                 ret
  41
  42
  43 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  44 ; Open file.
  45 ;
  46 ; return:
  47 ;    al         0: ok, 1: file not found
  48 ;   ecx         file length (al = 0)
  49 ;
  50 cb_fopen:
  51                 mov si,f_name
  52                 push ds
  53                 pop es
  54                 mov ax,6
  55                 int 22h
  56                 xchg edx,eax
  57                 mov al,1
  58                 jc cb_fopen_90
  59                 cmp cx,[f_buf_size]
  60                 ja cb_fopen_90
  61                 or cx,cx
  62                 jz cb_fopen_90
  63                 mov [f_block_size],cx
  64                 or edx,edx
  65                 jz cb_fopen_90
  66                 mov [f_handle],si
  67                 mov [f_size],edx
  68                 mov ecx,edx
  69                 mov ax,[f_buf_size]
  70                 cwd
  71                 div word [f_block_size]
  72                 mov [f_blocks],ax
  73
  74                 xor al,al
  75 cb_fopen_90:
  76                 ret
  77
  78
  79 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  80 ; Read next chunk.
  81 ;
  82 ; return:
  83 ;   edx         buffer address (linear)
  84 ;   ecx         data length (< 64k)
  85 ;
  86 cb_fread:
  87                 xor ecx,ecx
  88                 mov si,[f_handle]
  89                 or si,si
  90                 jz cb_fread_80
  91                 mov cx,[f_blocks]
  92                 mov es,[f_buf_seg]
  93                 xor bx,bx
  94                 mov ax,7
  95                 int 22h
  96                 mov [f_handle],si
  97                 mov al,1
  98                 jc cb_fread_90
  99 cb_fread_80:
 100                 xor al,al
 101 cb_fread_90:
 102                 movzx edx,word [f_buf_seg]
 103                 shl edx,4
 104                 ret
 105
 106
 107 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 108 ; Return current working directory.
 109 ;
 110 ; return:
 111 ;  edx          filename
 112 ;
 113 cb_getcwd:
 114                 mov ax,1fh
 115                 int 22h
 116                 mov edx,es
 117                 shl edx,4
 118                 movzx ebx,bx
 119                 add edx,ebx
 120                 xor al,al
 121                 ret
 122
 123
 124 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 125 ; Set current working directory.
 126 ;
 127 cb_chdir:
 128                 mov bx,f_name
 129                 push ds
 130                 pop es
 131                 mov ax,25h
 132                 int 22h
 133                 xor al,al
 134                 ret
 135
 136
 137 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 138 ; read sector
 139 ;
 140 ;  edx          sector
 141 ;
 142 ; return:
 143 ;  edx          buffer (linear address)
 144 ;
 145 ;  Note: does not return on error!
 146 ;
 147 cb_readsector:
 148                 xor edi,edi
 149                 xor esi,esi
 150                 mov cx,1
 151                 mov es,[f_buf_seg]
 152                 xor bx,bx
 153                 mov ax,19h
 154                 int 22h
 155                 movzx edx,word [f_buf_seg]
 156                 shl edx,4
 157                 xor al,al
 158                 ret
 159
 160
 161 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 162 ; Re-read fs structures.
 163 ;
 164 cb_mount:
 165                 mov ax,26h
 166                 int 22h
 167                 setc al
 168                 ret
 169
 170
 171 ; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 172 ;
 173                 align 2, db 0
 174
 175 cb_table        dw cb_status
 176                 dw cb_fopen
 177                 dw cb_fread
 178                 dw cb_getcwd
 179                 dw cb_chdir
 180                 dw cb_readsector
 181                 dw cb_mount
 182 cb_len          equ ($-cb_table)/2
 183
 184 f_handle        dw 0
 185 f_block_size    dw 0
 186 f_blocks        dw 0
 187 f_size          dd 0
 188 f_name          times 64 db 0
 189 f_name_len      equ $ - f_name
 190