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|
; Cheers to the BOOT12 bootloader for a lot of these handy definitions.
; Modified them slightly to fit the kernel's needs
;; TO DO: Confirm that these aren't destroyed as kernel loads
;%define s_per_clu 0x7C00+0x0D ; byte Sectors per cluster
;%define s_b4_fat 0x7C00+0x0E ; word Sectors (in partition) before FAT
;%define fats 0x7C00+0x10 ; byte Number of FATs
;%define dir_ent 0x7C00+0x11 ; word Number of root directory entries
;%define s_p_fat 0x7C00+0x16 ; word Sectors per FAT
;%define s_p_t 0x7C00+0x18 ; word Sectors per track
;%define heads 0x7C00+0x1A ; word Number of heads
;%define s_b4_prt 0x7C00+0x1C ; dword Sectors before partition
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; name: jaspos_disk_reset
;; @param disk disk number to reset
;; @return none
;; Resets the disk system
;;
jaspos_disk_reset:
push dx
push ax
mov dl, [Drive] ; DL = drive #
xor ah, ah ; AH = 0 = reset disk system
int 0x13 ; Perform the reset
pop ax
pop dx
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; name: jaspos_disk_readsector
;; @param buffer memory buffer to write sector into
;; @param sector relative sector number to load
;; @return none
;; Loads one sector from the boot disk into memory
;;
jaspos_disk_readsector:
pop bp ; Save CALL's address
pop cx ; Get sector number into CX
pop bx ; Get buffer location
push bp ; Push CALL's address back onto stack ready for RET
push cx
call jaspos_disk_make_chs ; Convert the sector number supplied into a useful CHS (cylinder, head, sector) triplet
;mov dl, [Drive] ; DL = Drive number
;xor dh, dh ; DH = Head
xor ch, ch ; CH = Track number
mov al, 1 ; AL = # Sectors to read
mov ah, 2 ; AH = Read command
int 0x13 ; Read sector
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; name: jaspos_disk_make_chs
;; @param sector relative sector number to load
;; @return CHS registers ready for INT13
;; Converts relative sector into CHS, ready for
;; interrupt 13
;;
jaspos_disk_make_chs:
pop bp
pop ax
push bp
xor dx, dx ; DIV's input is DXAX - clear DX so we're only dividing AX
div word [s_per_track] ; Sectors per track
inc dl ; Sectors start at 1, not 0
mov cl, dl ; Sectors belong in CL for int 13h
mov ax, bx
xor dx, dx ; Now calculate the head
div word [s_per_track] ; Sectors per track
xor dx, dx
div word [heads] ; Floppy sides
mov dh, dl ; Head/side
mov ch, al ; Track
mov dl, [Drive] ; Set correct device
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; name: jaspos_disk_get_info
;; @param none
;; @return none
;; Load the boot sector into memory and patches
;; the disk info (label, heads etc) into memory
;; for use by kernel
;;
jaspos_disk_get_info:
call jaspos_disk_reset ;
jc jaspos.panic ; If the reset fails, just panic
; We need to call INT13 manually, because jaspos_diskio_readsector
; relies on having the disk info we're about to load, loaded.
; Hooray for having to bootstrap
mov bx, free_ram ; Buffer location
mov dl, [Drive] ; DL = Drive number
xor dh, dh ; DH = Head
xor ch, ch ; CH = Track number
mov al, 1 ; AL = # Sectors to read
mov ah, 2 ; AH = Read command
int 0x13 ; Read sector
mov di, msgDiskLabel + 13 ; Load the disk label into the disk label message
mov si, free_ram+0x2B ; The label starts 0x2B bytes into the sector
mov cx, 11d ; Disk labels are 11 bytes long on FAT12
rep movsb ; Copy 11 bytes from the sector buffer into the inside of
mov cx, 25d ; There are 25d bytes that I want copied and saved
mov si, free_ram+0x0B ; Start copying from byte 0x0B
mov di, b_per_s ; Start storing at the b_per_s label
rep movsb ; Copy the bytes
ret ; the disk label message, thus filling it with the disk label
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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