Another attempt on disk i/o
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@ -3,6 +3,7 @@
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jmp 0:(init+0x7C00-$$)
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%include "inc/bpb.asm"
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%include "inc/mbr.asm"
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; Far call via interrupt vector
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%macro intcall 1
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@ -195,7 +196,7 @@ fputc: push ax
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%include "kernel/diskio.asm"
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vects: dw int20h, int21h, retf, retf
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dw retf, int25h, int26h, int20h
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dw retf, retf, retf, int20h
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dw idle, fputc
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main: ; zero out first 64kb except our code
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@ -222,12 +223,7 @@ intlp: movsw
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call dnconv
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mov al, dl
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mov cx, 1
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mov dx, 0
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mov bx, buffer
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int 3
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intcall 0x25
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int 3
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call select
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loop: int 0x28
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jmp loop
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@ -250,6 +246,3 @@ init: cli
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section .bss
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; stack to be used during init and disk i/o
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stack: resw stacks
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; default int 25h/26h handler use a cache to keep geometry for
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; the first 4 drives
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buffer: resb 512
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11
inc/mbr.asm
Normal file
11
inc/mbr.asm
Normal file
@ -0,0 +1,11 @@
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mbrtab: equ 0x1BE ; start of partition table
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mbrsig: equ 0x1FE ; start of signature
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mbrmn: equ 0x55AA ; signature value
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pardn: equ 0x00 ; byte: partition active flag
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parchs: equ 0x01 ; 3 bytes: CHS for first sector
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partyp: equ 0x04 ; byte: partition type
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parend: equ 0x05 ; 3 bytes: CHS for last sector
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paroff: equ 0x08 ; dword: partition offset in sectors
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parlen: equ 0x0C ; dword: partition length in sectors
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parsiz: equ 0x10
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@ -1,11 +1,23 @@
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section .bss
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chsspt: equ 0 ; word sectors per track
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chsnos: equ 2 ; word number of sides
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chspo: equ 4 ; dword partition offset
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chssiz: equ 8
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disk_buffer:
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resb 512
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chstab: resw (4*chssiz)
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disk_current:
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resb 1
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lba_supported:
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resb 1
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disk_chs: ; DL, DH, CL, CH for int 13h CHS functions
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resb 4
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disk_dap: ; disk access packet for int 13h EBIOS functions
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resb 0x10
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disk_tracks: ; heads * spt
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resw 1
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disk_spt:
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resb 1
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; Disk access packet for EBIOS extensions
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dapps: equ 0 ; byte packet size
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@ -28,121 +40,77 @@ dncl: rcl dl, 1
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xchg dh, dl
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ret
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fndchs: ; find CHS table entry
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; IN dl DOS drive number (A=0, B=1, ...)
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; OUT cs:si ptr to chs table entry
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push ax
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mov ax, chssiz
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mul dl
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add ax, chstab
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mov si, ax
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pop ax
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ret
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; compare sector number in disk access packet with zero
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; sets zero flag accordingly
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iszero: push ax
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mov ax, [bx]
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or ax, [bx+2]
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pop ax
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ret
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; calculate CHS from dap and CHS table entry
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; IN ds:bx disk access packet
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; cs:si chstab table entry
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; OUT cx,dh chs data for int 13h
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calchs: push ax
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; load linear sector number
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mov dx, [bx+2]
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mov ax, [bx]
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; if any word of it is non-zero, we need to do calculation
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call iszero
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jz .zero
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; ax is track number (lba / spt)
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; dx is sector (lba % spt) + 1
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div word [cs:si+chsspt]
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inc dx
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; sector number
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mov cl, dl
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; ax is cylinder (track / heads)
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; dx is head (track % heads)
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xor dx, dx
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div word [cs:si+chsnos]
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; set up cylinder and head number
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mov ch, al
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mov dh, dl
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pop ax
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ret
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; set up CHS data for int 13h for reading sector zero
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.zero: mov cx, 1 ; C=0, S=1
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mov dh, 0 ; H=0
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pop ax
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ret
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; ABSOLUTE DISK READ / DISK WRITE
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int25h: mov ah, 2
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jmp adisk
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int26h: mov ah, 3
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adisk: push bp
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push ds
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push es
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mov bp, sp
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push ax
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cmp cx, 0xFFFF
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je .lrg
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; build ebios DAP from registers supplied
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; qword sector number
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push cs
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push cs
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push cs
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push dx
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; dword target buffer
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push ds
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push bx
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; word number of sectors
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push cx
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jmp .psz
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.lrg: ; build ebios DAP from int 25h DAP
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; qword sector number
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push cs
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push cs
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mov ax, [bx+2]
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push ax
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mov ax, [bx]
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push ax
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; dword target buffer
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mov ax, [bx+8]
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push ax
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mov ax, [bx+6]
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push ax
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; word number of sectors
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mov ax, [bx+4]
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push ax
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.psz: ; word packet size
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mov ax, dapsiz
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push ax
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; DS:SI = SS:SP (ptr to dap)
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push ss
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pop ds
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mov si, sp
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; set up int 13h subfunction number
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mov ax, [si+dapsiz]
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add ah, 0x40
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; get BIOS drive number
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mov dl, al
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; Select a drive for I/O
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; IN dl 0=A, 1=B, 2=C, 3=D
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select: mov byte [disk_current], 0xFF
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mov byte [lba_supported], 0
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cmp dl, 0x02
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jc select_floppy
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; detect EBIOS/LBA extensions
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call dnconv
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mov byte [disk_chs], dl
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mov ah, 0x41
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mov bx, 0x55AA
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int 0x13
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test cx, 1
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jz .nolba
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cmp bx, 0xAA55
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jnz .nolba
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mov byte [lba_supported], 1
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.nolba: call seek_zero
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ret
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.ret: mov sp, bp
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select_floppy:
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xor dx, dx
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xor ax, ax
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call seek
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call read
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ret
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; Set absolute sector number
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; IN dx:ax 32-bit sector number
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seek: push ax
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or ax, dx
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pop ax
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jz seek_zero
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; dx:ax = lba
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div word [disk_tracks]
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xchg ax, dx
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; dx = cylinder, ax = head * spt + sector
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div byte [disk_spt]
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; dx = cylinder, al = head, ah = sector
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xchg dl, dh
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ror dl, 1
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ror dl, 1
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or dl, ah
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;inc dx
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; dh bit 0-7: cylinder 0-7
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; dl bit 0-5: sector number 0-5
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; dl bit 6-7: cylinder 8-9
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; store
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mov byte [disk_chs+1], al
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mov word [disk_chs+2], dx
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int 3
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ret
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seek_zero:
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mov byte [disk_chs+1], 0
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mov word [disk_chs+2], 1
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ret
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; Read a sector into buffer
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read: mov ax, 0x0201
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mov dx, [disk_chs]
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mov cx, [disk_chs+2]
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lea bx, [disk_buffer]
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push cs
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pop es
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pop ds
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pop bp
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retf
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int 3
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int 0x13
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int 3
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ret
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; Write a sector into buffer
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write:
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ret
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