Make kernel and fat.bs use BPB struct
This commit is contained in:
parent
303b1756e0
commit
9cd4c04c42
11
Makefile
11
Makefile
@ -1,4 +1,4 @@
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FLOPPY = 360
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FLOPPY = 1440
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PROGRAMS = hello.com
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DISTFILES = $(PROGRAMS) kernel.bs
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@ -55,15 +55,6 @@ fat4.bs: boot/fat.asm
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fat6.bs: boot/fat.asm
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$(NASM) $(NASM_ARGS) -DFAT16 -DCHS -DLARGE -o $@ $<
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fatb.bs: boot/fat.asm
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$(NASM) $(NASM_ARGS) -DFAT32 -DCHS -DLARGE -o $@ $<
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fatc.bs: boot/fat.asm
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$(NASM) $(NASM_ARGS) -DFAT32 -DLBA -DLARGE -o $@ $<
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fate.bs: boot/fat.asm
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$(NASM) $(NASM_ARGS) -DFAT16 -DLBA -DLARGE -o $@ $<
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# BIOS option roms
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%.rom: rom/%.asm utils/fix-rom
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$(NASM) $(NASM_ARGS) -o $@ $< && utils/fix-rom $@
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526
boot/fat.asm
526
boot/fat.asm
@ -1,338 +1,270 @@
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; Bootsector for FAT32 filesystems
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; Takes defines:
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; FAT12 FAT has 1.5 bytes per entry
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; FAT16 FAT has WORD per entry
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; FAT32 FAT has DWORD per entry
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; CHS uses int13h/AH=02h
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; LARGE requires 32 bit sector numbers
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; LBA uses int13h/AH=42h
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cpu 8086
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; Bootsector for FAT12/FAT16 filesystems
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; Takes defines:
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; FAT12 FAT has 1.5 bytes per entry
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; FAT16 FAT has WORD per entry
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cpu 8086
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org 0x0800
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jmp short init
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nop
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org 0x0800
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jmp short init
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nop
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%include "inc/bpb.asm"
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%include "inc/bpb.asm"
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bpb: equ 0x080B
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times ( 0x0B - ($-$$) ) db 0
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; Area for BPB
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%ifdef FAT32
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times ( 0x5A - ($-$$) ) db 0
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%else
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times ( 0x3E - ($-$$) ) db 0
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%endif
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params: times bpb_size db 0
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init: xor ax, ax
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mov ss, ax
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mov sp, 0x7C00
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; Area for BPB
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times ( 0x3E - ($-$$) ) db 0
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; save potential partition table entry
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push ds
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push si
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init: xor ax, ax
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mov ss, ax
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mov sp, 0x7C00
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mov ds, ax
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mov es, ax
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; save potential partition table entry
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push ds
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push si
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mov si, 0x7C00
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mov di, 0x0800
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mov cx, 0x0100
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rep movsw
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jmp 0x0:main
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mov ds, ax
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mov es, ax
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%include "inc/booterr.asm"
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mov si, 0x7C00
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mov di, 0x0800
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mov cx, 0x0100
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rep movsw
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jmp 0x0:main
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; offsets relative to FS
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readd: ; add offset of cluster data area to DX:AX
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push cx
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mov di, [bp+bpb_rde]
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mov cl, 4
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shr di, cl ; 32 bytes per entry
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add ax, di
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adc dx, 0
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pop cx
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readr: ; add offset to rootdir to DX:AX (FAT12/FAT16 only)
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push cx
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xor ch, ch
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mov cl, byte [bp+bpb_fn]
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fatlp:
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%ifdef FAT32
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add ax, [bp+bpb7_lsf]
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adc dx, [bp+bpb7_lsf+2]
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%else
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add ax, [bp+bpb_sf]
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adc dx, 0
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%endif
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loop fatlp
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pop cx
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readf: ; add offset to FAT table to DX:AX
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add ax, word [bp+bpb_rsc]
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adc dx, 0
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readp: ; read sector DX:AX from partition
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add ax, word [bp+bpb_po]
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adc dx, word [bp+bpb_po+2]
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jnc ($+5)
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call errcll
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%include "inc/booterr.asm"
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%ifdef LBA
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read_: ; read sector DX:AX from disk
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; this uses the EBIOS extensions
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; qword sector number DX:AX
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push cs
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push cs
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push dx
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push ax
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; offsets relative to FS
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readd: ; add offset of cluster data area to DX:AX
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push cx
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mov di, [bp+bpb.direntries]
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mov cl, 4
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shr di, cl ; 32 bytes per entry
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add ax, di
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adc dx, 0
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pop cx
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readr: ; add offset to rootdir to DX:AX (FAT12/FAT16 only)
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push cx
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xor ch, ch
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mov cl, byte [bp+bpb.fatnumber]
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fatlp: add ax, [bp+bpb.fatsectors]
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adc dx, 0
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loop fatlp
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pop cx
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readf: ; add offset to FAT table to DX:AX
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add ax, word [bp+bpb.reservedsects]
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adc dx, 0
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readp: ; read sector DX:AX from partition
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add ax, word [bp+bpb.sectoroffset]
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adc dx, word [bp+bpb.sectoroffset+2]
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jnc ($+5)
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call errcll
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; dword target buffer: BX:0
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push bx
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push cs
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read_: ; read sector DX:AX from disk
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; uses basic CHS disk IO
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; this cant reliable read over track boundaries
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; so we read each single sector in loop over CX
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chslp: push ax
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push cx
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push dx
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push bx
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; word sector number
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push cx
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; calculate CHS data
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div word [bp+bpb.tracksectors] ; 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 [bp+bpb.heads] ; 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, [bp+bpb.drivenum] ; drive number
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; size & passing
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mov di, 0x10
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push di
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; set up read buffer
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mov es, bx
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xor bx, bx
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mov si, sp
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mov ah, 0x42
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mov dl, [bp+bpb7_dn]
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stc
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int 0x13
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jnc ($+5)
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call errcll
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; call bios
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mov ax, 0x0201
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int 0x13
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jnc ($+5)
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call errcll
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add sp, di
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pop bx
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pop dx
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pop cx
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pop ax
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ret
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%endif
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; increment sector num + write offset
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add ax, 1
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adc dx, 0
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add bx, 0x20
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; loop on CX
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loop chslp
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ret
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%ifdef CHS
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read_: ; read sector DX:AX from disk
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; uses basic CHS disk IO
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; this cant reliable read over track boundaries
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; so we read each single sector in loop over CX
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chslp: push ax
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push cx
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push dx
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push bx
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next: ; Advances DX:AX to next FAT entry
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push ax
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push bx
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; shift 2 left for dword-sized FAT entries
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; shift 9 right for sector size
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mov cl, 7
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shftl: clc
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rcr dx, 1
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rcr ax, 1
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loop shftl
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; calculate CHS data
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div word [bp+bpb_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 [bp+bpb_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, [bp+bpb7_dn] ; drive number
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mov bx, 0xA0
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%ifdef FAT12
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; FAT item might span over two sectors
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mov cx, 2
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%else
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mov cx, 1
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%endif
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call readf
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; set up read buffer
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mov es, bx
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xor bx, bx
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pop bx
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; call bios
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mov ax, 0x0201
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int 0x13
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jnc ($+5)
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call errcll
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; get address of cluster within sector
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pop si
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%ifdef FAT12
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push si
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; times 1.5
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mov ax, si
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shr ax, 1
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add si, ax
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add si, buf
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lodsw
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pop si
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test si, 1
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jz .odd
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.even: mov cl, 4
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shr ax, cl
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jmp .done
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.odd: and ax, 0x0FFF
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.done: xor dx, dx
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%endif
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pop bx
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pop dx
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pop cx
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pop ax
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%ifdef FAT16
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; double
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sal si, 1
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; make sure its within sector range
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and si, 0x1FF
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add si, buf
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; load word
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lodsw
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xor dx, dx
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%endif
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; increment sector num + write offset
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add ax, 1
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adc dx, 0
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add bx, 0x20
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; loop on CX
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loop chslp
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ret
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%endif
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ret
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next: ; Advances DX:AX to next FAT entry
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push ax
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push bx
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; shift 2 left for dword-sized FAT entries
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; shift 9 right for sector size
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mov cl, 7
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shftl: clc
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rcr dx, 1
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rcr ax, 1
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loop shftl
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; reads current cluster into [dest]
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readc: ; load cluster number
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push ax
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push dx
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mov bx, 0xA0
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%ifdef FAT12
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; FAT item might span over two sectors
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mov cx, 2
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%else
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mov cx, 1
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%endif
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call readf
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; subtract the two dummy entries from FAT start
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sub ax, 2
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sbb dx, 0
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pop bx
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; get address of cluster within sector
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pop si
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%ifdef FAT12
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push si
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; times 1.5
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mov ax, si
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shr ax, 1
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add si, ax
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add si, buf
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lodsw
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pop si
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test si, 1
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jz .odd
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.even: mov cl, 4
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shr ax, cl
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jmp .done
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.odd: and ax, 0x0FFF
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.done: xor dx, dx
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%endif
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%ifdef FAT16
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; double
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sal si, 1
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; make sure its within sector range
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and si, 0x1FF
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add si, buf
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; load word
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lodsw
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xor dx, dx
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%endif
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%ifdef FAT32
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; multiply with 4
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sal si, 1
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sal si, 1
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; make sure its within sector range
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and si, 0x1FF
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add si, buf
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; load dword
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lodsw
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mov dx, [si]
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%endif
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ret
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; reads current cluster into [dest]
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readc: ; load cluster number
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push ax
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push dx
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; subtract the two dummy entries from FAT start
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sub ax, 2
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sbb dx, 0
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; convert cluster number to sector number
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; this is some cheapo multiplication with 2^n
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mov cl, [bp+bpb_sc]
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l02: shr cl, 1
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jz l02e
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clc
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rcl ax, 1
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rcl dx, 1
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jmp l02
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; convert cluster number to sector number
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; this is some cheapo multiplication with 2^n
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mov cl, [bp+bpb.clustersects]
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l02: shr cl, 1
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jz l02e
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clc
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rcl ax, 1
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rcl dx, 1
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jmp l02
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l02e:
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; dx:ax is now sector num in data area
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mov cx, [bp+bpb_sc]
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xor ch, ch
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; dx:ax is now sector num in data area
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mov cx, [bp+bpb.clustersects]
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xor ch, ch
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call readd
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call readd
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xchg di, cx
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mov cl, 5
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sal di, cl
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add bx, di
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xchg di, cx
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mov cl, 5
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sal di, cl
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add bx, di
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pop dx
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pop ax
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pop dx
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pop ax
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ret
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ret
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; Load root directory
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loadr:
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%ifdef FAT32
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mov ax, 2
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xor dx, dx
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jmp load
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%else
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mov ax, [bp+bpb_rde]
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mov cl, 4
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shr ax, cl
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mov cx, ax
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xor ax, ax
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xor dx, dx
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mov bx, 0x07C0
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jmp readr
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%endif
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; Load root directory
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loadr: mov ax, [bp+bpb.direntries]
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mov cl, 4
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shr ax, cl
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mov cx, ax
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xor ax, ax
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xor dx, dx
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mov bx, 0x07C0
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jmp readr
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; Load file identified by fsattr
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; Directory data is expected at 0x07C00
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loadf: mov si, (0x7C00-0x20)
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sloop: add si, 0x20
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; check if entry is valid
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mov al, [si]
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; unallocated direntry
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test al, al
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jnz ($+5)
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call errcll
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; deleted files
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cmp al, 0xE2
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je sloop
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; check attr
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mov al, [si+11]
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and al, 0x5C
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cmp al, ah
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jne sloop
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mov ax, [si+0x1A]
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mov dx, [si+0x14]
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; Load file identified by fsattr
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; Directory data is expected at 0x07C00
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loadf: mov si, (0x7C00-0x20)
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sloop: add si, 0x20
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; check if entry is valid
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mov al, [si]
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; unallocated direntry
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test al, al
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jnz ($+5)
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call errcll
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; deleted files
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cmp al, 0xE2
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je sloop
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; check attr
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mov al, [si+11]
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and al, 0x5C
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cmp al, ah
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jne sloop
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mov ax, [si+0x1A]
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mov dx, [si+0x14]
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; Load cluster chain DX:AX to 0x07C00
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load: mov bx, 0x07C0
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lloop: call readc
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call next
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%ifdef FAT12
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cmp word ax, 0x0FF8
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%endif
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%ifdef FAT16
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cmp word ax, 0xFFF8
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%endif
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%ifdef FAT32
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cmp word dx, 0x0FFF
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%endif
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jc lloop
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ret
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; Load cluster chain DX:AX to 0x07C00
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load: mov bx, 0x07C0
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lloop: call readc
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call next
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%ifdef FAT12
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cmp word ax, 0x0FF8
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%endif
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%ifdef FAT16
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cmp word ax, 0xFFF8
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%endif
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jc lloop
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ret
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main: ; Set up BP to point to BPB
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; Relative addressing saves one instruction byte per access
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mov bp, bpb
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; Save DL contents
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mov [bp+bpb7_dn], dl
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main: ; Set up BP to point to BPB
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; Relative addressing saves one instruction byte per access
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mov bp, params
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; Save DL contents
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mov [bp+bpb.drivenum], dl
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; load root directory
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call loadr
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; search for first system directory
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mov ah, 0x14
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call loadf
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; search for first system file
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mov ah, 0x04
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call loadf
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; load root directory
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call loadr
|
||||
|
||||
; restore drive number
|
||||
mov dl, [bp+bpb7_dn]
|
||||
; search for first system directory
|
||||
mov ah, 0x14
|
||||
call loadf
|
||||
; search for first system file
|
||||
mov ah, 0x04
|
||||
call loadf
|
||||
|
||||
; restore potential partition table
|
||||
pop si
|
||||
pop ds
|
||||
; restore drive number
|
||||
mov dl, [bp+bpb.drivenum]
|
||||
|
||||
jmp 0x7C00
|
||||
; restore potential partition table
|
||||
pop si
|
||||
pop ds
|
||||
|
||||
; Padding and signature
|
||||
times (0x1FE - ($-$$)) db 0
|
||||
dw 0xAA55
|
||||
jmp 0x7C00
|
||||
|
||||
; Padding and signature
|
||||
times (0x1FE - ($-$$)) db 0
|
||||
dw 0xAA55
|
||||
buf:
|
||||
|
||||
46
inc/bpb.asm
46
inc/bpb.asm
@ -1,29 +1,17 @@
|
||||
; DOS 3.31 Bios Parameter Block
|
||||
bpb_ss: equ 0x00 ; WORD sector size
|
||||
bpb_sc: equ 0x02 ; BYTE sector / cluster
|
||||
bpb_rsc: equ 0x03 ; WORD reserved sector count
|
||||
bpb_fn: equ 0x05 ; BYTE fat number
|
||||
bpb_rde: equ 0x06 ; WORD root dir entries
|
||||
bpb_ts: equ 0x08 ; WORD total sectors
|
||||
bpb_md: equ 0x0A ; BYTE media descriptor
|
||||
bpb_sf: equ 0x0B ; WORD sectors / fat
|
||||
bpb_spt: equ 0x0D ; WORD sectors per track
|
||||
bpb_nos: equ 0x0F ; WORD number of sides
|
||||
bpb_po: equ 0x11 ; DWORD partition offset
|
||||
bpb_lts: equ 0x15 ; DWORD large total sectors
|
||||
|
||||
; DOS 4.0 Extended Bios Parameter Block
|
||||
bpb4_dn: equ 0x19 ; BYTE drive number
|
||||
bpb4_sig: equ 0x1B ; BYTE 29h
|
||||
bpb4_ser: equ 0x1C ; DWORD serial
|
||||
|
||||
; DOS 7.1 Extended Bios Parameter Block
|
||||
bpb7_lsf: equ 0x19 ; DWORD large sectors / fat
|
||||
bpb7_rdc: equ 0x21 ; DWORD root directory cluster
|
||||
bpb7_fsc: equ 0x25 ; WORD fsinfo sector
|
||||
bpb7_bsc: equ 0x27 ; WORD backup boot sector
|
||||
bpb7_dn: equ 0x35 ; BYTE drive number
|
||||
bpb7_sig: equ 0x37 ; BYTE 28h or 29h
|
||||
bpb7_ser: equ 0x38 ; DWORD serial
|
||||
|
||||
bpb_len: equ 0x4F
|
||||
struc bpb
|
||||
.sectorsize: resw 1 ; WORD sector size
|
||||
.clustersects: resb 1 ; BYTE sector / cluster
|
||||
.reservedsects: resw 1 ; WORD reserved sector count
|
||||
.fatnumber: resb 1 ; BYTE fat number
|
||||
.direntries: resw 1 ; WORD root dir entries
|
||||
.total: resw 1 ; WORD total sectors
|
||||
.mediadesc: resb 1 ; BYTE media descriptor
|
||||
.fatsectors: resw 1 ; WORD sectors / fat
|
||||
.tracksectors: resw 1 ; WORD sectors per track
|
||||
.heads: resw 1 ; WORD number of sides
|
||||
.sectoroffset: resd 1 ; DWORD partition offset
|
||||
.longtotal: resd 1 ; DWORD large total sectors
|
||||
.drivenum: resb 1 ; BYTE drive number
|
||||
.signature: resb 1 ; BYTE 28h
|
||||
.serial: resd 1 ; DWORD serial
|
||||
endstruc
|
||||
|
||||
Loading…
Reference in New Issue
Block a user