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Implement reading of BPB from FAT partition

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This commit is contained in:
Nero 2020-05-07 22:56:37 +00:00
parent 8d28dc9f85
commit a472c396e7
1 changed files with 27 additions and 7 deletions
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34
kernel/diskio.asm
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@ -65,6 +65,7 @@ select: mov byte [disk_current], 0xFF
jmp select_hdd jmp select_hdd
select_floppy: select_floppy:
push dx
call seek_zero call seek_zero
call read call read
; load disk geometry ; load disk geometry
@ -76,17 +77,30 @@ select_floppy:
; we dont rely on the 'total sectors' given in the BPB ; we dont rely on the 'total sectors' given in the BPB
; instead, we assume maximum cylinder ; instead, we assume maximum cylinder
; 1023 is the maximum encodable for int 13h ; 1023 is the maximum encodable for int 13h
mov di, 1023 lea di, [part_offset]
mul di
mov [part_size], ax
mov [part_size+2], dx
; set partition offset to zero
xor ax, ax xor ax, ax
mov [part_offset], ax ; partition offset = 0
mov [part_offset+2], ax stosw
stosw
; partition size = 0x00010000 = 32MB
stosw
inc ax
stosw
pop dx
ret ret
select_hdd: select_hdd:
push dx
; load CHS geometry for drive
mov ah, 0x8
int 0x13
xor ah, ah
mov al, cl
mov [disk_spt], ax
mul byte dh
mov [disk_spc], ax
; load offset and size of first partition
call seek_zero call seek_zero
call read call read
mov bx, disk_buffer+0x1BE mov bx, disk_buffer+0x1BE
@ -94,6 +108,12 @@ select_hdd:
lea di, [part_offset] lea di, [part_offset]
mov cx, 4 mov cx, 4
rep movsw rep movsw
; read bpb
mov dx, [part_offset+2]
mov ax, [part_offset]
call seek
call read
pop dx
ret ret
; Set absolute sector number ; Set absolute sector number