Use COM-based format, get bootloader working
This commit is contained in:
parent
11b4d07dc1
commit
d853b87ec7
12
Makefile
12
Makefile
@ -25,8 +25,8 @@ endif
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default: kernel.rom
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kernel.rom: kernel/*.asm lib/*.inc
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nasm -s -o $@ -I lib -I kernel kernel/main.asm && scripts/fix-rom.sh $@
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kernel.com: kernel/*.asm lib/*.inc
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nasm -s -o $@ -I lib -I kernel kernel/main.asm
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debug.rom: debug/*.asm lib/*.inc
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nasm -s -o $@ -I lib -I debug debug/main.asm && scripts/fix-rom.sh $@
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@ -34,11 +34,11 @@ debug.rom: debug/*.asm lib/*.inc
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boot/%.bin: boot/%.asm lib/*.inc
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nasm -s -o $@ -I boot -I lib $<
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fdimage.img: boot/floppy.bin kernel.rom
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fdimage.img: boot/floppy.bin kernel.com
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dd if=/dev/zero bs=512 count=$$(( $(FD_CYLINDERS) * $(FD_HEADS) * $(FD_SECTORS) )) of=$@
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mformat -i $@ -t $(FD_CYLINDERS) -h $(FD_HEADS) -n $(FD_SECTORS) -B boot/floppy.bin ::
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mcopy -i $@ kernel.rom ::kernel.rom
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mattrib -i $@ +s ::kernel.rom
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mcopy -i $@ kernel.com ::kernel.com
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mattrib -i $@ +s ::kernel.com
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clean:
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rm -f *.com *.bin *.rom *.img *.log boot/*.bin
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@ -47,7 +47,7 @@ qemu-rom: kernel.rom $(DEBUGROM)
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$(QEMU) $(QEMU_ARGS) -option-rom kernel.rom
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qemu-floppy: fdimage.img $(DEBUGROM)
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$(QEMU) $(QEMU_ARGS) -boot c -hda fdimage.img
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$(QEMU) $(QEMU_ARGS) -boot c -fda fdimage.img
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qemu-serial: boot/serial.bin $(DEBUGROM)
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$(QEMU) $(QEMU_ARGS) -hda boot/serial.bin
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47
boot/chs.inc
47
boot/chs.inc
@ -1,47 +0,0 @@
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fix_chs:
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mov ah, 0x08
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int 0x13
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jc chs_end ; skip if function does not exist
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inc dh
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mov [cs:fdc.nos], dh
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push cx
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and cx, 0x003F
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mov [cs:fdc.spt], cx ; no adjustment because sectors are 1-indexed
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pop ax
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xchg al, ah
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mov cl,6
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shr ah,cl
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inc ax ; convert from maximum number (0-based) to total number (1-based) of cylinders
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mul word [cs:fdc.nos] ; number of tracks = number of cylinders * heads
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mul word [cs:fdc.spt] ; number of sectors = number of tracks * sectors per track
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mov [cs:fdc.ts], ax
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jmp chs_end
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; Load a single sector into memory
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; Does not return on error
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; in dx:ax sector number (will be trashed)
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; es:bx buffer
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load_sector:
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push cx
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div word [cs:fdc.spt] ; ax:temp = (lba / spt)
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inc dx ; dx:sector = (lba % spt) + 1
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mov cl, dl ; sector number
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xor dx, dx
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div word [cs:fdc.nos] ; ax:cylinder = (tmp / heads)
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; dx:head = (tmp % heads)
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mov ch, al ; cylinder number
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mov dh, dl ; head number
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mov dl, [cs:fdc.drv] ; driver number
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mov ax, 0x0201 ; ah=0x02 al=0x01
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int 0x13
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jc disk_error
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; return
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pop cx
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ret
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disk_error:
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xchg al, ah
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call error
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db "DISK ERROR", 0
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chs_end:
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289
boot/floppy.asm
289
boot/floppy.asm
@ -1,8 +1,17 @@
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org 0x0000
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org 0x7600
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jmp 0x07C0:main
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; Memory layout:
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; 060:0000 PSP for loaded program
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; 060:0100 Loaded program
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; 060:7800 Our code (= 0:7C00)
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; 060:8000 FAT table
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; 060:E000 Root directory
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; 060:FF00 Stack area
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times (0x0B - ($-$$)) db 0 ; space-padded
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init:
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jmp 0x060:main
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times (0x0B - ($-$$)) db 0
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fdc:
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.ss:
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dw 0x200 ; sector size
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@ -41,119 +50,207 @@ fdc:
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db "FAT12"
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times (62 - ($-$$)) db " "
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main:
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cli
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; setup stack area growing down from directly below us
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xor ax, ax
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mov ss, ax
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mov sp, 0x7C00
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; setup base segments
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mov ax, cs
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mov ds, ax
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mov es, ax
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; save initial environment
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push bx
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; Read sectors from disk
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; Does not return on error
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; ax and bx will be incremented, cx decremented
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; in dx:ax sector number
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; es:bx buffer
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; cx number of sectors to read
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; out dx:ax next sector to read
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; es:bx next free buffer
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; cx zero
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load_sectors:
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; fail instantly if reading sectors > 16 bit
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test dx, dx
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mov bp, 0x0030
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jnz error
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.loop:
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push ax
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push cx
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push dx
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mov [fdc.drv], dl ; fix drive number in fdc
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; calculate CHS data
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div word [cs:fdc.spt] ; ax:temp = (lba / spt)
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inc dx ; dx:sector = (lba % spt) + 1
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mov cl, dl ; sector number
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xor dx, dx
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div word [cs:fdc.nos] ; ax:cylinder = (tmp / heads)
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; dx:head = (tmp % heads)
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mov ch, al ; cylinder number
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mov dh, dl ; head number
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mov dl, [cs:fdc.drv] ; driver number
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mov ax, 0x0201 ; ah=0x02 al=0x01
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int 0x13
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mov bp, 0x0031
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jc error
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%include "chs.inc"
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pop dx
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pop cx
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pop ax
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mov di, 0x1000 ; loading address for roms
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call search_rootdir
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; count up for next sector
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add bx, 0x0200
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inc ax
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mov ax, 0xFFFF
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call error
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db "THING", 0
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loop .loop
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ret
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search_rootdir:
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; Load the file in [filename]
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; or exit with carry set
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load_file:
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mov si, 0xE000
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mov cx, [fdc.rde]
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.loop:
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call file_match
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je read_clusters
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add si, 0x20
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loop .loop
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ret
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; Compares the FAT dirent against [filename]
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; in ds:si filename
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; out ZF zero flag set if equal
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file_match:
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push cx
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push si
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mov di, filename
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mov cx, 11
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repe cmpsb
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pop si
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pop cx
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ret
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; Read the file given by cluster number
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; into the target program area
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; in ax cluster number
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read_clusters:
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add si, 0x1A
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lodsw
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mov bx, 0x0100
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.loop:
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; read cluster into area for target file
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push ax
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sub ax, 2
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mul BYTE [fdc.sc]
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add ax, [cluster_offset]
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xor dx, dx
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mov cx, [fdc.sc]
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xor ch, ch
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call load_sectors
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pop ax
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; calculate index in FAT
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mov si, ax
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shr si, 1
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add si, ax
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add si, 0x8000
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; load entry from FAT, truncate to 12 bit
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mov dx, [si]
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test ax, 1
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jz .noshift
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mov cl, 4
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shr dx, 4
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.noshift:
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mov ax, dx
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and ax, 0x0FFF
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cmp ax, 0x0FF8
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jc .loop
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ret
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main:
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cli
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; Everything in one segment, stack starts on top
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mov ax, cs
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mov ds, ax
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mov es, ax
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mov ss, ax
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mov sp, ax
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mov [fdc.drv], dl ; save drive number in fdc
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sti
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; load fat table into memory
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mov ax, [fdc.rsc]
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mov cx, [fdc.sf]
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xor dx, dx
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mov bx, 0x8000
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call load_sectors
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; calculate length of rootdir
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mov ax, [fdc.rde]
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dec ax
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mov cl, 4
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shr ax, cl ; 32 bytes per entry
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inc ax
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mov cx, ax
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; load root dir
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xor dx, dx
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mov ax, [fdc.sf]
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mul byte [fdc.fn]
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add ax, [fdc.rsc]
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mul word [fdc.ss]
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mov si, ax ; now pointing to start of rootdir
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mov cx, [fdc.rde]
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jmp .start
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.next:
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dec cx
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jz .end
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add si, 0x20
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.start:
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call lazy_load
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cmp byte [si], 0 ; end of directory
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je .end
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cmp byte [si], 0xe5 ; deleted entry
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je .next
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cmp word [si+8], 0x4F52 ; first 2 chars of extension: "RO"
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jne .next
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mov ax, [si+10] ; 3rd char of extension, file flags
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and ax, 0x14FF ; zero out flags except directory and system
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cmp ax, 0x044D ; "M" , system flag set, directory flag unset
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jne .next
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mov ax, [si+26]
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push si
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push cx
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call loadrom
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pop cx
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pop si
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jmp .next
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.end:
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ret
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mov bx, 0xE000
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call load_sectors
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; in ax cluster number
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loadrom:
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call print16
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ret
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; remember where we left off
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; clusters start after rootdir
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mov [cluster_offset], ax
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; Makes sure the block starting with (or under SI) is
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; already fetched from disk
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; in ds:si data expected to be fetched from disk
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; trashes ax, bx and dx
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lazy_load:
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cmp si, [max_si]
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jc .end
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; calculate next sector number
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mov ax, [max_si]
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call load_file
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mov bp, 0x0032
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jc error
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; get length of arguments
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mov cx, 0x007F
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mov di, arguments
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xor ax, ax
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repe scasb
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sub di, arguments
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mov cx, di
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; setup arguments field
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mov [0x080], cl
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mov di, [0x081]
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mov si, arguments
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rep movsb
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; setup int 19h call at 0000, and push its address to stack
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mov WORD [0000], 0x19CD
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push sp
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; clear out registers and jump into target
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xor ax, ax
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xor cx, cx
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xor dx, dx
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div word [fdc.ss]
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; write to es:bx
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xor dx, dx
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push cs
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pop es
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mov bx, [max_si]
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call load_sector
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; update max_si counter
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mov ax, [max_si]
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add ax, [fdc.ss]
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mov [max_si], ax
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; loop until requirement is satisfied
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jmp lazy_load
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.end:
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ret
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xor bx, bx
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mov dl, [fdc.drv]
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jmp 0x0100
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error:
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call print16
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pop si
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mov bx, 0x0000
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mov al, 0x20
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.loop:
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mov ax, bp
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mov ah, 0x0e
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mov bx, 7
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int 0x10
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lodsb
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cmp al, 0x00
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jne .loop
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.hlt:
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hlt
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jmp .hlt
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mov al, 0x21
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int 0x10
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xor ax, ax
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int 0x16
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int 0x19
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%include "print.asm"
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cluster_offset:
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dw 0
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times (0x1FA - ($-$$)) db 0
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times (0x175 - ($-$$)) db 0
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dw 0x2B2B
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filename:
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db "KERNEL COM"
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max_si:
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dw 0x200
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arguments:
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db " ", 0
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times (0x1FE - ($-$$)) db 0
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dw 0xAA55
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@ -1,60 +1,5 @@
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cpu 8086
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org 0x0000
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rom:
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db 0x55, 0xAA
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.sectors:
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db 0x00
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.init:
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push cs
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pop es
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mov di, start
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mov ax, 0x18
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call intr_register
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retf
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.name:
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db "ROM DOS", 0
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times (0x18 - ($-$$)) db 0
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.pcir_ptr:
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dw 0
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times (0x1A - ($-$$)) db 0
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.pnp_ptr:
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dw pnp
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pnp:
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db "$PnP"
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.version:
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db 1 ; version 1
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.length:
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db 2 ; 2 * 16 length
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dw 0 ; offset of next header
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db 0
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.checksum:
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db 0 ; checksum (filled by fix-rom)
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dd 0 ; device identifier
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dw 0 ; manufacturer string
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dw rom.name ; product name string
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db 0,0,0 ; device type string
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db 0x20 ; device indicator, bit for "read cacheable" set
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dw 0 ; boot connection vector
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dw 0 ; boot disconnect vector
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dw start ; bootstrap entry point
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dw 0 ; reserved
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dw 0
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start:
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xor ax, ax
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mov ds, ax
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mov es, ax
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mov ss, ax
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mov sp, 0x800
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mov di, sp
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call drvtab_create
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org 0x0100
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push cs
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pop es
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mov di, isr_dos_main
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@ -64,7 +9,6 @@ start:
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.loop:
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mov ah, 0x01
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int 0x21
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int3
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jmp .loop
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cli
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@ -91,4 +35,4 @@ isr_return:
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%include "chario.asm"
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align 512
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times 1000 db 0xEA
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