177 lines
2.4 KiB
NASM
177 lines
2.4 KiB
NASM
[ORG 0x7c00]
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jmp short start
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nop
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;1.44 MB 3.5" floppy disk description table
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OEMLabel db "EttinOS "
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BytesPerSector dw 0x200
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SectorsPerCluster db 0x1
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BootRecordSectors dw 0x1
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FATs db 0x2
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RootEntries dw 0xe0
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LogicalSectors dw 0xb40
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MediaDescriptor db 0xf0
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SectorsPerFAT dw 0x9
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SectorsPerTrack dw 0x12
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Sides dw 0x2
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HiddenSectors dd 0x0
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LargeSectors dd 0x0
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DriveNumber dw 0x0
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DriveSignature db 0x29
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VolumeID dd 0x0
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VolumeLabel db "EttinOS "
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FileSystem db "FAT12 "
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start:
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;Set up the data segment
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mov ax, 0x0
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mov ds, ax
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;Set up the stack
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cli
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mov ax, 0x0
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mov ss, ax
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mov sp, 0x7c00
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sti
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;Store the boot device number
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mov [bootdev], dl
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;Load the root FAT
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;Set the source
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mov ax, 0x13
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call calcsource
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;Set the destination
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mov si, 0x7e00
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mov bx, ds
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mov es, bx
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mov bx, si
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;Set the size
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mov al, 0xe
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;Load
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mov ah, 0x2
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int 0x13
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;Search the root FAT for the system
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;Set DI to the root FAT
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mov ax, ds
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mov es, ax
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mov di, 0x7e00
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;Initialise the search loop
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mov cx, word [RootEntries]
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mov ax, 0x0
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search:
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;Store CX in the stack
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push cx
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;Check for the binary
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mov si, sysfile
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mov cx, 0xb
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rep cmpsb
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je loadsysfat
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;Set DI to the next entry
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add ax, 0x20
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mov di, 0x7e00
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add di, ax
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;Load CX from the stack
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pop cx
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loop search
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;Load the system FAT
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loadsysfat:
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;???
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mov ax, word [es:di+0xf]
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mov word [cluster], ax
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;Set the source
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mov ax, 0x1
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call calcsource
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;Set the destination
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mov di, 0x7e00
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mov bx, di
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;Set the size
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mov al, 0x9
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;Load
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mov ah, 0x2
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int 0x13
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;Load the system
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loadsys:
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;Set the source
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mov ax, word [cluster]
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add ax, 0x1f
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call calcsource
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;Set the destination
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mov ax, 0x0
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mov es, ax
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mov bx, word [pointer]
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;Set the size
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mov al, 0x1
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;Load a cluster
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mov ah, 0x2
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int 0x13
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;Calculate the next cluster
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mov ax, [cluster]
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mov dx, 0x0
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mov bx, 0x3
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mul bx
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mov bx, 2
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div bx
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mov si, 0x7e00
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add si, ax
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mov ax, word [ds:si]
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or dx, dx
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jz even
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odd:
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shr ax, 4
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jmp contcluster
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even:
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and ax, 0xfff
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contcluster:
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mov word [cluster], ax
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cmp ax, 0xff8
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jge boot
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add word [pointer], 0x200
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jmp loadsys
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boot:
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jmp 0x0:0x9e00
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sysfile:
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db "SYSTEM BIN"
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bootdev:
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db 0
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cluster:
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dw 0x0
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pointer:
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dw 0x9e00
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calcsource:
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push ax
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push bx
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mov bx, ax
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mov dx, 0x0
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div word [SectorsPerTrack]
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add dl, 0x1
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mov cl, dl
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mov ax, bx
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mov dx, 0x0
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div word [SectorsPerTrack]
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mov dx, 0x0
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div word [Sides]
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mov dh, dl
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mov ch, al
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pop bx
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pop ax
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mov dl, byte [bootdev]
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ret
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;Padding
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times 0x1fe-($-$$) db 0x0
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;Boot signature
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dw 0xaa55
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