implemented chainloading from hd

diff --git a/bb.asm b/bb.asm
index 743dc9f..73bd68d 100644 (file)
--- a/bb.asm
+++ b/bb.asm
@@ -22,6 +22,30 @@
        out dx, al
 %endmacro
 
+bios_param_block:
+       jmp start       ; 2 bytes
+       nop             ; 1 byte
+       ; start of BPB at offset 3
+       db "BSPL 0.1"   ; 03h: OEM ident, 8 bytes
+       dw 512          ; 0bh: bytes per sector
+       db 1            ; 0dh: sectors per cluster
+       dw 1            ; 0eh: reserved sectors (including boot record)
+       db 2            ; 10h: number of FATs
+       dw 224          ; 11h: number of dir entries
+       dw 2880         ; 13h: number of sectors in volume
+       db 0fh          ; 15h: media descriptor type (f = 3.5" HD floppy)
+       dw 9            ; 16h: number of sectors per FAT
+       dw 18           ; 18h: number of sectors per track
+       dw 2            ; 1ah: number of heads
+       dd 0            ; 1ch: number of hidden sectors
+       dd 0            ; 20h: high bits of sector count
+       db 0            ; 24h: drive number
+       db 0            ; 25h: winnt flags
+       db 28h          ; 26h: signature(?)
+       dd 0            ; 27h: volume serial number
+       db "BOOTBOOT   "; 2bh: volume label, 11 bytes
+       db "FAT12   "   ; 36h: filesystem id, 8 bytes
+
 start:
        mov sp, 7c00h
 
@@ -186,8 +210,8 @@ main_loop:
        add ax, bx
        sub di, ax
        call rand
-       and ax, 3               ; random value in 0, 15
-       sub ax, 1               ; random value in -3, 12
+       and ax, 3               ; random value in 0, 2
+       sub ax, 1               ; random value in -1, 1
        add di, ax
        mov si, lovebug
        call blit32
@@ -242,6 +266,23 @@ main_loop:
        call print_num
        mov si, str_newline
        call print_str
+
+       mov dx, 80h             ; default to load from drive 80h
+       cmp byte [saved_drive_num], 80h
+       jnz .not_hd
+       inc dl                  ; next hd
+.not_hd:
+; load hard disk boot sector
+       xor ax, ax
+       mov es, ax
+       mov bx, 7c00h
+       mov ah, 02h
+       mov al, 1
+       mov ch, 0
+       mov cl, 1
+       mov dh, 0
+       int 13h
+       jnc 7c00h
 .inf_loop:
        jmp .inf_loop