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kernel: implement diskio using drive table

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This commit is contained in:
Nero 2020-08-27 20:52:16 +00:00
parent 4a294ee21c
commit f0a000b7d1
5 changed files with 93 additions and 259 deletions
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84
kernel/drive.asm
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@ -16,6 +16,13 @@ drive_ptr: resw 1
drive_table: resb (drives * drive_size)
; DX and CX for int 13 CHS access
chs_dx: resw 1
chs_cx: resw 1
; disk buffer for I/O operations
diskbuf: resb 1024
section .text
drives_init: ; CX = number of floppy drives in the system
@ -32,6 +39,7 @@ drives_init: ; CX = number of floppy drives in the system
.loop: push cx
push dx
mov [bx+drive.biosnum], dl
mov byte [bx+drive.flag], 1 ; 1 = drive letter used
; query bios for floppy format
mov ah, 8
push bx
@ -82,3 +90,79 @@ drives_init: ; CX = number of floppy drives in the system
add bx, drive_size
loop .loop
ret
; select drive
; IN dl drive number
drive_select: xor dh, dh
mov ax, drive_size
mul dx
add ax, drive_table
mov word [drive_ptr], ax
ret
; reset currently selected drive
drive_reset: mov bx, [drive_ptr]
mov dl, [bx+drive.biosnum]
; our ptr = CX:BX
lea bx, [bx+drive.dpt]
mov cx, ds
; toggle in our ptr
mov si, [0x1E*4]
xchg bx, [si]
xchg cx, [si+2]
; do the call
xor ax, ax
int 0x13
pushf
; restore original ptr
xchg bx, [si]
xchg cx, [si+2]
; pass int 13 flags
popf
ret
; query status of selected drive
; OUT ah
drive_status: mov bx, [drive_ptr]
mov dl, [bx+drive.biosnum]
mov ah, 1
int 0x13
ret
; set sector for read/write operation
; IN dx:ax 32-bit sector number
drive_seek: mov bx, [drive_ptr]
div word [bx+drive.spc]
xchg ax, dx
; dx = cylinder, ax = head * spt + sector
div byte [bx+drive.dpt+dpt.lastsector]
; dx = cylinder, al = head, ah = sector
xchg dl, dh
ror dl, 1
ror dl, 1
or dl, ah
inc dx
; al: head number
; dh bit 0-7: cylinder bits 0-7
; dl bit 0-5: sector bits 0-5
; dl bit 6-7: cylinder bits 8-9
xchg al, ah
mov al, [bx+drive.biosnum]
; store
mov word [chs_dx], ax
mov word [chs_cx], dx
ret
drive_read: mov ax, 0x0201
mov cx, [chs_cx]
mov dx, [chs_dx]
mov bx, diskbuf
int 0x13
ret
drive_write: mov ah, 0x0301
mov cx, [chs_cx]
mov dx, [chs_dx]
mov bx, diskbuf
int 0x13
ret