Set BPB data from the BIOS, properly support loading data from sectors >63, calculate CHS addressing properly. Calculate certain important values rather than harcoding them.
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8f1e13e749
commit
26d231a7c9
GPG Key ID:
45AC398F44F0DAFE
122
boot.asm
122
boot.asm
@ -1,24 +1,28 @@
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[BITS 16] ;tell the assembler that its a 16 bit code
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[BITS 16]
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jmp short bootcode
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nop
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bpOEMid db "XNOE "
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bpBytesPerSector dw 512
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bpSectorsPerCluster db 1
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bpReservedSectors dw 1
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bpNoFATs db 2
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bpRootDirEntries dw 256
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bpLVSectors dw 8419
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bpMediumID db 0F0h
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bpSectorsPerFat dw 9
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bpLVSectors dw 8586
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bpMediumID db 0xF8
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bpSectorsPerFat dw 34
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bpSectorsPerTrack dw 18
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bpSides dw 2
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bpHiddenSectors dd 0
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bpLargeSectors dd 0
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bpDriveNo dw 0
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bpSignature db 41
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bpVolumeID dd 00000000h
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bpHeads dw 2
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bpHiddenSectors dw 0
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TIMES 36 - ($ - $$) db 0
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bpDriveNo db 0
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db 0
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bpSignature db 0x29
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bpVolumeID dd 0x0
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bpVolumeLabel db "XNOE OS "
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bpFileSystem db "FAT16 "
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@ -26,7 +30,18 @@ bootcode:
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mov ax, 7c0h
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mov ds, ax
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mov byte [drive], dl
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mov byte [bpDriveNo], dl
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; Get the disk configuration from the BIOS
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mov ah, 08h
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int 13h
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add dh, 1
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movzx dx, dh
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mov word [bpHeads], dx
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and cl, 03fh
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movzx cx, cl
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mov word [bpSectorsPerTrack], cx
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mov si, boot_msg
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call _boot_print
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@ -35,12 +50,13 @@ bootcode:
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mov es, ax
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mov bx, buffer
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mov ah, 2
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mov al, 16
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mov cl, 20
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mov ch, 0
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mov dh, 0
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mov dl, byte [drive]
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; Calculate position of rootdirentries
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mov ax, word [bpSectorsPerFat]
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movzx cx, byte [bpNoFATs]
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mul cx
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add ax, 2
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call prep_i13
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int 13h
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@ -57,11 +73,6 @@ kernel_finder:
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mov di, buffer
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add di, ax
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; mov si, di
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; call _boot_print
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; mov si, new_line
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; call _boot_print
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mov si, kernel_file
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mov cx, 11
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rep cmpsb
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@ -78,6 +89,7 @@ kernel_finder:
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jmp $
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kernel_found:
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; jmp $
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mov ax, [es:di+0fh]
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mov word [cluster], ax
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@ -86,29 +98,41 @@ fat_loader:
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mov es, ax
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mov bx, buffer
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mov ax, word [bpSectorsPerFat]
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mov ah, 2
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mov al, 9
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mov cl, 2
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mov ch, 0
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mov dh, 0
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mov dl, byte [drive]
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mov dl, byte [bpDriveNo]
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int 13h
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kernel_loader:
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; Calculate file offset
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mov ax, word [bpSectorsPerFat]
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movzx cx, byte [bpNoFATs]
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mul cx
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push ax
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mov ax, word [bpRootDirEntries]
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mov cx, 16
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div cx
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mov bx, ax
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pop ax
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add ax, bx
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mov word [fileoffset], ax
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mov ax, 2000h
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mov es, ax
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mov bx, word [pointer]
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mov al, byte [cluster]
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add al, 34
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movzx ax, byte [cluster]
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add ax, word [fileoffset]
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mov cl, al
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mov al, 1
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mov ah, 2
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mov ch, 0
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mov dh, 0
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mov dl, byte [drive]
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call prep_i13
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int 13h
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@ -117,7 +141,6 @@ kernel_loader:
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mov si, word [cluster]
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shl si, 1
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add si, buffer
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; add si, 1
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cmp word [si], 0ffffh
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je kernel_loaded
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@ -125,10 +148,6 @@ kernel_loader:
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jmp kernel_loader
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kernel_loaded:
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; Pass boot device to the kernel
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xor ax, ax
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mov al, byte [drive]
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push ax
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jmp 2000h:0h
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_boot_print:
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@ -149,11 +168,34 @@ kernel_nf db "KERNEL.BIN Missing!", 13, 10, 0
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new_line db " ", 0
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kernel_file db "KERNEL BIN"
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fileoffset dw 0
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cluster dw 0
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pointer dw 0
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drive db 0
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TIMES 510 - ($ - $$) db 0 ;fill the rest of sector with 0
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DW 0xAA55 ; add boot signature at the end of bootloader
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; AX set to the logical sector number.
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prep_i13:
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xor dx, dx
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div word [bpSectorsPerTrack]
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push dx
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xor dx, dx
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div word [bpHeads]
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mov ch, al
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mov dh, dl
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mov dl, byte [bpDriveNo]
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pop ax
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mov cl, al
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mov al, 1
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mov ah, 2
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ret
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TIMES 510 - ($ - $$) db 0
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DW 0xAA55
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buffer:
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106
kernel.asm
106
kernel.asm
@ -1,3 +1,17 @@
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bpBytesPerSector equ 0x0b
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bpSectorsPerCluster equ 0x0d
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bpReservedSectors equ 0x0e
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bpNoFATs equ 0x10
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bpRootDirEntries equ 0x11
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bpLVSectors equ 0x13
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bpMediumID equ 0x15
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bpSectorsPerFat equ 0x16
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bpSectorsPerTrack equ 0x18
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bpHeads equ 0x1a
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bpHiddenSectors equ 0x1c
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bpDriveNo equ 0x24
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bpSignature equ 0x26
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[BITS 16]
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; Update the IVT with our interrupt handler
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mov bx, 0
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@ -8,40 +22,59 @@
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mov ax, 2000h
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mov ds, ax
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pop ax
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mov byte [bootdisk], al
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mov ax, 7c0h
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mov fs, ax
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; Set up kernel specifics
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; Root Directory Entries will be at 2000h:2000h
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; FAT1 will be at 2000h:4000h
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; Load sectors RDE to 2000h:2000h
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mov ax, 2000h
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mov es, ax
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mov bx, 2000h
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mov ah, 2
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mov al, 16
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mov cl, 20
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mov ch, 0
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mov dh, 0
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mov dl, [bootdisk]
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; Load sectors 20 through 36 to 2000h:2000h
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; Calculate position of RDE
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mov ax, word [fs:bpSectorsPerFat]
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movzx cx, byte [fs:bpNoFATs]
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mul cx
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add ax, 2
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call prep_i13
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mov al, 16
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int 13h
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; Load sectors 2 through 36 to 2000h:4000h
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mov ax, 2000h
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mov es, ax
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mov bx, 4000h
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mov ax, 2
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call prep_i13
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mov ax, word [fs:bpSectorsPerFat]
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mov ah, 2
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mov al, 9
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mov cl, 2
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mov ch, 0
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mov dh, 0
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mov dl, [bootdisk]
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; Load sectors 2 through 11 to 2000h:4000h
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int 13h
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; Calculate file offset
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mov ax, word [fs:bpSectorsPerFat]
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movzx cx, byte [fs:bpNoFATs]
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mul cx
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push ax
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mov ax, word [fs:bpRootDirEntries]
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mov cx, 16
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div cx
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mov bx, ax
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pop ax
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add ax, bx
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mov word [fileoffset], ax
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push msg
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call print
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@ -165,8 +198,6 @@ data:
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newline db 13, 10, 0
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bootdisk db 0
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program_two db "HELLO BIN"
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@ -300,6 +331,9 @@ load_file:
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mov bp, sp
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push ds
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push fs
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mov ax, 7c0h
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mov fs, ax
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mov ax, 2000h
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mov ds, ax
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@ -308,16 +342,9 @@ load_file:
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load_file_loop:
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mov bx, word [bp + 6]
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mov al, byte [bp + 8]
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add al, 34
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mov cl, al
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mov al, 1
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mov ah, 2
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mov ch, 0
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mov dh, 0
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mov dl, byte [bootdisk]
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movzx ax, byte [bp + 8]
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add ax, word [fileoffset]
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call prep_i13
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int 13h
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@ -334,6 +361,7 @@ load_file_loop:
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jmp load_file_loop
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load_file_loaded:
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pop fs
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pop ds
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pop bp
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ret 6
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@ -369,7 +397,6 @@ decode_filename_loop:
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decode_filename_stage2:
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mov bx, 8
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mov cx, 3
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; add si, 1
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decode_filename_stage2_loop:
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@ -419,3 +446,26 @@ _ihdlr_4:
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_ihdlr_5:
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_ihdlr_fin:
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iret
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prep_i13:
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xor dx, dx
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div word [fs:bpSectorsPerTrack]
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push dx
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xor dx, dx
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div word [fs:bpHeads]
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mov ch, al
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mov dh, dl
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mov dl, byte [fs:bpDriveNo]
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pop ax
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mov cl, al
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mov al, 1
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mov ah, 2
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ret
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fileoffset dw 0
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