303 lines
7.1 KiB
NASM
303 lines
7.1 KiB
NASM
; FAT12 boot sector for Kolibri OS
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;
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; Copyright (C) Alex Nogueira Teixeira
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; Copyright (C) Diamond
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; Copyright (C) Dmitry Kartashov aka shurf
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;
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; Distributed under GPL, see file COPYING for details
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;
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; Version 1.0
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lf equ 0ah
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cr equ 0dh
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pos_read_tmp equ 0700h ;position for temporary read
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boot_program equ 07c00h ;position for boot code
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seg_read_kernel equ 01000h ;segment to kernel read
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jmp start_program
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nop
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; Boot Sector and BPB Structure
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BS_OEMName db 'KOLIBRI ' ; db 8
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BPB_BytsPerSec dw 512 ; bytes per sector
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BPB_SecPerClus db 1 ; sectors per cluster
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BPB_RsvdSecCnt dw 1 ; number of reserver sectors
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BPB_NumFATs db 2 ; count of FAT data structures
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BPB_RootEntCnt dw 224 ; count of 32-byte dir. entries (224*32 = 14 sectors)
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BPB_TotSec16 dw 2880 ; count of sectors on the volume (2880 for 1.44 mbytes disk)
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BPB_Media db 0f0h ; f0 - used for removable media
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BPB_FATSz16 dw 9 ; count of sectors by one copy of FAT
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BPB_SecPerTrk dw 18 ; sectors per track
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BPB_NumHeads dw 2 ; number of heads
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BPB_HiddSec dd 0 ; count of hidden sectors
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BPB_TotSec32 dd 0 ; count of sectors on the volume (if > 65535)
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BS_DrvNum db 0 ; int 13h drive number
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BS_Reserved db 0 ; reserved
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BS_BootSig db 29h ; Extended boot signature
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BS_VolID dd 0 ; Volume serial number
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BS_VolLab db 'KOLIBRI ' ; Volume label (db 11)
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BS_FilSysType db 'FAT12 ' ; file system type (db 8)
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start_program:
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xor ax,ax
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mov ss,ax
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mov sp,boot_program
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push ss
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pop ds
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; print loading string
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mov si,loading+boot_program
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loop_loading:
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lodsb
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or al,al
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jz read_root_directory
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mov ah,0eh
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mov bx,7
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int 10h
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jmp loop_loading
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read_root_directory:
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push ss
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pop es
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; calculate some disk parameters
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; - beginning sector of RootDir
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mov ax,word [BPB_FATSz16+boot_program]
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xor cx,cx
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mov cl,byte [BPB_NumFATs+boot_program]
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mul cx
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add ax,word [BPB_RsvdSecCnt+boot_program]
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mov word [FirstRootDirSecNum+boot_program],ax ; 19
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mov si,ax
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; - count of sectors in RootDir
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mov bx,word [BPB_BytsPerSec+boot_program]
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mov cl,5 ; divide ax by 32
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shr bx,cl ; bx = directory entries per sector
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mov ax,word [BPB_RootEntCnt+boot_program]
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xor dx,dx
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div bx
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mov word [RootDirSecs+boot_program],ax ; 14
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; - data start
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add si,ax ; add beginning sector of RootDir and count sectors in RootDir
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mov word [data_start+boot_program],si ; 33
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; reading root directory
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; al=count root dir sectrors !!!! TODO: al, max 255 sectors !!!!
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mov ah,2 ; read
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push ax
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mov ax,word [FirstRootDirSecNum+boot_program]
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call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector)
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pop ax
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mov bx,pos_read_tmp ; es:bx read buffer
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call read_sector
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mov si,bx ; read buffer address: es:si
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mov ax,[RootDirSecs+boot_program]
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mul word [BPB_BytsPerSec+boot_program]
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add ax,si ; AX = end of root dir. in buffer pos_read_tmp
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; find kernel file in root directory
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loop_find_dir_entry:
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push si
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mov cx,11
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mov di,kernel_name+boot_program
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rep cmpsb ; compare es:si and es:di, cx bytes long
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pop si
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je found_kernel_file
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add si,32 ; next dir. entry
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cmp si,ax ; end of directory
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jb loop_find_dir_entry
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file_error_message:
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mov si,error_message+boot_program
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loop_error_message:
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lodsb
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or al,al
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jz freeze_pc
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mov ah,0eh
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mov bx,7
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int 10h
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jmp loop_error_message
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freeze_pc:
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jmp $ ; endless loop
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; === KERNEL FOUND. LOADING... ===
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found_kernel_file:
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mov bp,[si+01ah] ; first cluster of kernel file
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; <diamond>
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mov [cluster1st+boot_program],bp ; starting cluster of kernel file
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; <\diamond>
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; reading first FAT table
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mov ax,word [BPB_RsvdSecCnt+boot_program] ; begin first FAT abs sector number
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call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector)
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mov bx,pos_read_tmp ; es:bx read position
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mov ah,2 ; ah=2 (read)
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mov al, byte [BPB_FATSz16+boot_program] ; FAT size in sectors (TODO: max 255 sectors)
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call read_sector
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jc file_error_message ; read error
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mov ax,seg_read_kernel
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mov es,ax
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xor bx,bx ; es:bx = 1000h:0000h
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; reading kernel file
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loop_obtains_kernel_data:
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; read one cluster of file
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call obtain_cluster
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jc file_error_message ; read error
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; add one cluster length to segment:offset
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push bx
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mov bx,es
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mov ax,word [BPB_BytsPerSec+boot_program] ;\
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movsx cx,byte [BPB_SecPerClus+boot_program] ; | !!! TODO: !!!
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mul cx ; | out this from loop !!!
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shr ax,4 ;/
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add bx,ax
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mov es,bx
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pop bx
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mov di,bp
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shr di,1
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pushf
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add di,bp ; di = bp * 1.5
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add di,pos_read_tmp
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mov ax,[di] ; read next entry from FAT-chain
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popf
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jc move_4_right
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and ax,0fffh
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jmp verify_end_sector
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move_4_right:
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mov cl,4
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shr ax,cl
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verify_end_sector:
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cmp ax,0ff8h ; last cluster
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jae execute_kernel
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mov bp,ax
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jmp loop_obtains_kernel_data
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execute_kernel:
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; <diamond>
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mov ax,'KL'
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push 0
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pop ds
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mov si,loader_block+boot_program
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; </diamond>
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push word seg_read_kernel
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push word 0
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retf ; jmp far 1000:0000
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;------------------------------------------
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; loading cluster from file to es:bx
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obtain_cluster:
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; bp - cluster number to read
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; carry = 0 -> read OK
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; carry = 1 -> read ERROR
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; print one dot
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push bx
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mov ax,0e2eh ; ah=0eh (teletype), al='.'
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xor bh,bh
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int 10h
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pop bx
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writesec:
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; convert cluster number to sector number
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mov ax,bp ; data cluster to read
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sub ax,2
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xor dx,dx
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mov dl,byte [BPB_SecPerClus+boot_program]
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mul dx
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add ax,word [data_start+boot_program]
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call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector)
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patchhere:
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mov ah,2 ; ah=2 (read)
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mov al,byte [BPB_SecPerClus+boot_program] ; al=(one cluster)
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call read_sector
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retn
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;------------------------------------------
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;------------------------------------------
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; read sector from disk
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read_sector:
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push bp
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mov bp,20 ; try 20 times
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newread:
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dec bp
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jz file_error_message
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push ax bx cx dx
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int 13h
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pop dx cx bx ax
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jc newread
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pop bp
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retn
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;------------------------------------------
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; convert abs. sector number (AX) to BIOS T:H:S
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; sector number = (abs.sector%BPB_SecPerTrk)+1
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; pre.track number = (abs.sector/BPB_SecPerTrk)
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; head number = pre.track number%BPB_NumHeads
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; track number = pre.track number/BPB_NumHeads
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; Return: cl - sector number
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; ch - track number
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; dl - drive number (0 = a:)
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; dh - head number
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conv_abs_to_THS:
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push bx
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mov bx,word [BPB_SecPerTrk+boot_program]
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xor dx,dx
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div bx
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inc dx
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mov cl, dl ; cl = sector number
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mov bx,word [BPB_NumHeads+boot_program]
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xor dx,dx
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div bx
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; !!!!!!! ax = track number, dx = head number
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mov ch,al ; ch=track number
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xchg dh,dl ; dh=head number
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mov dl,0 ; dl=0 (drive 0 (a:))
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pop bx
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retn
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;------------------------------------------
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loading db cr,lf,'Starting system ',00h
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error_message db 13,10
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kernel_name db 'KERNEL MNT ?',cr,lf,00h
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FirstRootDirSecNum dw ?
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RootDirSecs dw ?
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data_start dw ?
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; <diamond>
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write1st:
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push cs
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pop ds
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mov byte [patchhere+1+boot_program], 3 ; change ah=2 to ah=3
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mov bp,[cluster1st+boot_program]
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push 1000h
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pop es
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xor bx,bx
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call writesec
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mov byte [patchhere+1+boot_program], 2 ; change back ah=3 to ah=2
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retf
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cluster1st dw ?
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loader_block:
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db 1
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dw 0
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dw write1st+boot_program
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dw 0
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; <\diamond>
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times 0x1fe-$ db 00h
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db 55h,0aah ;boot signature
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