lifeboot.asm

   1 bits 16
   2 org 0x7c00
   3
   4 %define ORG 0x7c00
   5 %define VGA 0xb8000
   6
   7 %define COLS 80
   8 %define ROWS 25
   9
  10 %define GRID ORG + 512
  11 %define NEXT_GRID GRID_CUR + COLS * ROWS
  12
  13 %define DEAD ' '
  14 %define ALIVE '#'
  15
  16 %define PRINT_COLOR 0x07            ; grey on black
  17
  18 ; entry point -----------------------------------------------------------------
  19
  20 ; initialize segment registers
  21 xor ax, ax
  22 mov ds, ax
  23 mov es, ax
  24 mov ss, ax
  25
  26 ; set stack pointers
  27 mov sp, ORG
  28 mov bp, ORG
  29
  30 ; clear screen ----------------------------------------------------------------
  31
  32 ; disable cursor
  33 mov ch, 0x3f
  34 mov ah, 0x01
  35 int 0x10
  36
  37 ; clear video memory
  38 mov cx, COLS * ROWS
  39 mov ax, VGA >> 4
  40 mov es, ax
  41 xor di, di
  42 mov ax, (PRINT_COLOR << 8) | DEAD
  43
  44 rep stosw                   ; fill cx words at es:di with ax
  45
  46 ; errors ----------------------------------------------------------------------
  47
  48 hello:
  49 mov si, str.hello
  50
  51 ; print the error message string in si and halt
  52 ; note: we assume es = VGA_SEG and ds = 0
  53 printerr:
  54 xor di, di
  55 mov ah, PRINT_COLOR
  56
  57 ; es:di = video memory
  58 ; ds:si = error message
  59 ; al = current char
  60 ; ah = color attribute
  61
  62 write_char:
  63 lodsb                   ; al = [ds:si], si += 1
  64 or  al, al              ; on null terminator,
  65 jz  halt                ;  halt
  66 stosw                   ; [es:di] = ax, di += 2
  67 jmp write_char
  68
  69 halt:
  70 cli                     ; disable interrupts
  71 hlt
  72 jmp halt
  73
  74 ; data ------------------------------------------------------------------------
  75
  76 str:
  77 .hello:
  78     db "lifeboot", 0
  79
  80 times 510 - ($ - $$) db 0   ; fill remaining bytes with zeroes
  81 dw 0xaa55                   ; mbr magic byte