diff options
| -rw-r--r-- | stage1/main.asm | 97 |
1 files changed, 88 insertions, 9 deletions
diff --git a/stage1/main.asm b/stage1/main.asm index f14c1f0..e25b220 100644 --- a/stage1/main.asm +++ b/stage1/main.asm @@ -1,7 +1,6 @@ [org 0x7C00] %define KSTART 0x7E00 -%define KSECTORS (KSIZE + 511) / 512 boot: ; init segment registers @@ -43,17 +42,95 @@ load_stages: mov ebx, .msg call print_str - mov ah, 0x02 ; read sectors from drive - mov al, KSECTORS ; number of sectors - xor ch, ch ; cylinder=0 - mov cl, 2 ; sector=2 - xor dh, dh ; head=0 - mov bx, KSTART ; buffer + ; mov si, 18 ; sectors per track + ; mov di, 2 ; number of heads + ; check if hard drive + ; test dl, 0x80 + ; jz .start_load ; use defaults if not a hard drive + + ; backup dl + push dx + + ; get geometry + mov ah, 8 int 0x13 - jc .fail ; CF set on error - cmp al, KSECTORS ; check read sectors count + + ; restore dl + pop ax + mov dl, al + + movzx si, cl + and si, 0x3f + + movzx di, dh + inc di + +.start_load: + pusha + + mov ebx, .sectors + call print_str + movzx eax, si + call print_dec + call newline + + mov ebx, .heads + call print_str + movzx eax, di + call print_dec + call newline + + popa + + ; setup buffer + mov ax, KSTART/0x10 + mov es, ax + mov bx, 0 + + mov cl, 2 ; sector=2 + mov dh, 0 ; head=0 + mov ch, 0 ; cylinder=0 + +.load: + mov ah, 0x02 ; read sectors from drive + mov al, 1 ; number of sectors + int 0x13 + jc .fail ; CF set on error + + ; check read sectors count + cmp al, 1 jne .fail + ; increase buffer pointer + add bx, 512 + + ; check if finished + cmp bx, KSIZE + jae .success + + ; next sector + inc cl + movzx ax, cl + cmp ax, si + jbe .load + + ; next head + mov cl, 1 + inc dh + movzx ax, dh + cmp ax, di + jb .load + + ; next cylinder + mov dh, 0 + inc ch + jmp .load + +.success: + ; restore es + mov ax, 0 + mov es, ax + ret .fail: @@ -63,6 +140,8 @@ load_stages: .msg: db "loading stage2 and stage3 from disk", 10, 13, 0 .fail_msg: db "disk failure, try rebooting", 10, 13, 0 +.sectors: db "sectors per track: ", 0 +.heads: db "number of heads: ", 0 %include "stage1/print.asm" |