Pave way for supporting FAT16 and FAT12
This commit is contained in:
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e34accfcff
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31
Makefile
31
Makefile
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@ -48,20 +48,41 @@ vga11.com: cp437.bin
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%.bs: boot/%.asm
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$(NASM) $(NASM_ARGS) -o $@ $<
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# Special case: variations of FAT vbr
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fat1.bs: boot/fat.asm
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$(NASM) $(NASM_ARGS) -DFAT12 -DCHS -o $@ $<
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fat4.bs: boot/fat.asm
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$(NASM) $(NASM_ARGS) -DFAT16 -DCHS -o $@ $<
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fat6.bs: boot/fat.asm
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$(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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fdimage.img: fat.bs $(DISTFILES)
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mformat -C -i $@ -f $(FLOPPY) -B fat.bs ::
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mcopy -i $@ $(DISTFILES) ::
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fdimage.img: fat1.bs $(DISTFILES)
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mformat -C -i $@ -f $(FLOPPY) -B fat1.bs ::
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mmd -i $@ ::rdos
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mcopy -i $@ $(DISTFILES) ::rdos
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mattrib -i $@ +s ::rdos ::rdos/kernel.bs
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hdimage.img: mbr.bs fdimage.img
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cat mbr.bs fdimage.img >$@
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part.img: fat32.bs $(DISTFILES)
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part.img: fatc.bs $(DISTFILES)
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dd if=/dev/zero bs=1024 count=33k of=$@
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mformat -i $@ -F -B fat32.bs ::
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mformat -i $@ -F -B fatc.bs ::
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mmd -i $@ ::rdos
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mcopy -i $@ $(DISTFILES) ::rdos
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mattrib -i $@ +s ::rdos ::rdos/kernel.bs
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498
boot/fat.asm
498
boot/fat.asm
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@ -1,293 +1,289 @@
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; Bootsector for FAT12 filesystems
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; Memory layout:
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; 0000-03FF IVT
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; 0400-0500 Bios data area
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; 0501-0600 Stack for us
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; 0600-0800 This code
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org 0x0600
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; 0800-0A00 Buffer for disk
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buf: equ 0x0800
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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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jmp near init
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org 0x0800
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jmp short init
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nop
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; current cluster number
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cclus: dw 0
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; sector number in cluster
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csec: dw 0
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%include "inc/bpb.asm"
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times (0x0B - ($-$$)) db 0
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; BIOS PARAMETER BLOCK
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fdc: ; sector size
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.ss: dw 0x200
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; sectors per cluster
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.sc: db 2
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; reserved sector count
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.rsc: dw 1
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.fn: ; number of file allocation tables
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db 2
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.rde: ; number of root directory entries
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dw 0x70
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.ts: ; total number of sectors
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dw 720
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.mid: db 0xFD
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.sf: dw 2
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.spt: dw 9
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.nos: dw 2
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.po: dd 0
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.lrgts: ; large sector count - relevant if .ts is 0
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dd 0
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bpb: equ 0x080B
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; mformat keeps writing until here
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; if we place init earlier, code gets overwritten
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; this also marks the end for the BPB
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times (62 - ($-$$)) nop
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; Area for BPB
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times ( 0x5A - ($-$$) ) 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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; save potential partition table entry
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push ds
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push si
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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, 0x0600
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; Relocate and jump
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mov di, sp
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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 0:main
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jmp 0x0:main
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; Set adress for sector read/write
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; Number is relative to current partition
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; IN dx:ax sector number
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seek: push ax
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push dx
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push ds
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push cs
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pop ds
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; add partition offset (required for HDD)
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add ax, [fdc.po]
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adc dx, [fdc.po+2]
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; ax:temp = (lba / spt)
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; dx:sector = (lba % spt) + 1
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div word [fdc.spt]
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inc dx
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; Sector number (bits 0-5) into CL
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; This is blindly assumed to never exeed 63
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mov byte [.cl], dl
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; ax:cylinder = (tmp / heads)
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; dx:head = (tmp % heads)
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xor dx, dx
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div word [fdc.nos]
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; Cylinder number bit 0-7 into CH
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mov byte [.ch], al
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; Head number into DL
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mov byte [.dh], dl
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; Bits 8-9 of cylinder number into bits 6-7 of CL
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and ah, 0x03
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ror ah, 1
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ror ah, 1
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or byte [.cl], ah
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pop ds
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pop dx
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pop ax
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ret
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.cl: db 0
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.ch: db 0
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.dl: db 0
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.dh: db 0
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%include "inc/booterr.asm"
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; Read sector into ES:BX
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; Sector number has been previously set with seek
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read: 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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push dx
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; ah = int13 subfunction 2
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; al = read 1 sector
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mov ax, 0x0201
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; load seek data into registers
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mov cx, word [cs:seek.cl]
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mov dx, word [cs:seek.dl]
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int 0x13
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int 3
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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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; Get start sector of root dirrectory
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; OUT ax sector number
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dirsec: ; Multiply sectors per fat with number of fats
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mov ax, [cs:fdc.sf]
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mul byte [cs:fdc.fn]
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; Add number of reserved sectors
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add ax, [cs:fdc.rsc]
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ret
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; Get root directory length in sectors
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; OUT cx sectors
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dirlen: push ax
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mov ax, [cs:fdc.rde]
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mov di, [bp+bpb_rde]
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mov cl, 4
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shr ax, cl ; 32 bytes per entry
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mov cx, ax
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pop ax
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ret
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; Get first sector of data area
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; OUT ax sector number
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clusec: push cx
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call dirsec
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call dirlen
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add ax, cx
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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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ret: ret
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; Get total number of sectors
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; OUT: dx:ax number of sectors
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secnum: xor dx, dx
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mov ax, [cs:fdc.ts]
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test ax, ax
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jnz ret
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mov ax, [cs:fdc.lrgts]
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mov dx, [cs:fdc.lrgts+2]
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ret
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; Get number of clusters
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; OUT: ax number of clusters
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; Cant overflow for FAT16 :P
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clunum: push cx
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push dx
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call clusec
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mov cx, ax
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call secnum
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sub ax, cx
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sbb dx, 0
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mov cl, byte [cs:fdc.sc]
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xor ch, ch
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div cx
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pop dx
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pop cx
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ret
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; Scan current buffer for matching file
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; IN ds = cs
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; es = cs
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; OUT bx start cluster if file found
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; trashed if no match
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; carry is set if no file was found
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scadir:
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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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push si
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mov si, buf
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mov cx, 0x10
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.loop: push cx
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push si
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mov bx, [si+0x1A]
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mov di, .name
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mov cx, 11
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repe cmpsb
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pop si
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xor ch, ch
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mov cl, byte [bp+bpb_fn]
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fatlp: add ax, [bp+bpb7_lsf]
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adc dx, [bp+bpb7_lsf+2]
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loop fatlp
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pop cx
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je .found
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add si, 0x20
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loop .loop
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stc
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.found: pop si
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pop cx
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ret
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.name: db "HELLO "
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.ext: db "COM"
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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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fopen:
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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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; dword target buffer: BX:0
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push bx
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push cs
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; word sector number
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push cx
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; size & passing
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mov di, 0x10
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push di
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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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add sp, di
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ret
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%endif
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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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push ds
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push es
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cmp word [cclus], 0
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jne .err
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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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call dirsec
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call dirlen
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.loop: xor dx, dx
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mov bx, buf
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call seek
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call read
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call scadir
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jnc .found
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inc ax
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loop .loop
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.err: stc
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jmp .ret
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.found: mov [cclus], bx
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mov word [csec], 0
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.ret: pop es
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pop ds
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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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; set up read buffer
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mov es, bx
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xor bx, 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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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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fread: push ax
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push cx
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push dx
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; abort if there is no file opened
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cmp word [cs:cclus], 0
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je .err
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; get start sector for data area
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call clusec
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push ax
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; get current cluster number
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mov ax, [cs:cclus]
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; clusters are 2-indexed
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sub ax, 2
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; multiply that with sectors per cluster
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mov cl, [cs:fdc.sc]
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xor ch, ch
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mul word cx
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; add current cluster offset, cluster start and current sector
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pop cx
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add cx, [cs:csec]
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add ax, cx
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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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; dx:ax now point to the sector that should be read next
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call seek
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call read
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jc .err
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inc word [cs:csec]
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jmp .ret
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.err: ; in case of error, trash current state
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call fclose
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stc
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.ret: pop dx
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pop cx
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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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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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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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pop bx
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; get lower part of cluster number
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pop si
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%ifdef FAT16
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; double
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sal si, 1
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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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%endif
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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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%ifdef FAT16
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; load word from FAT
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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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; load dword from FAT
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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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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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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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pop dx
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pop ax
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ret
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; Reset open file info
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fclose: mov [cclus], bx
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mov word [csec], 0
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; Load root directory
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loadr: mov ax, 2
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xor dx, dx
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jmp load
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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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cmp word dx, 0x0FFF
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jne lloop
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ret
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main: mov [seek.dl], dl ; save drive number
|
||||
main: ; Set up BP to point to BPB
|
||||
; Relative addressing saves one instruction byte per access
|
||||
mov bp, bpb
|
||||
; Save DL contents
|
||||
mov [bp+bpb7_dn], dl
|
||||
|
||||
call fopen
|
||||
mov bx, 0x1100
|
||||
call fread
|
||||
; load root directory
|
||||
call loadr
|
||||
; search for first system directory
|
||||
mov ah, 0x14
|
||||
call loadf
|
||||
; search for first system file
|
||||
mov ah, 0x04
|
||||
call loadf
|
||||
|
||||
mov ax, 0x0100
|
||||
mov ds, ax
|
||||
mov es, ax
|
||||
call 0x100:0x100
|
||||
; restore drive number
|
||||
mov dl, [bp+bpb7_dn]
|
||||
|
||||
.hlt: hlt
|
||||
jmp .hlt
|
||||
; restore potential partition table
|
||||
pop si
|
||||
pop ds
|
||||
|
||||
jmp 0x7C00
|
||||
|
||||
; Padding and signature
|
||||
times (0x1FE - ($-$$)) db 0
|
||||
dw 0xAA55
|
||||
buf:
|
||||
|
|
|
|||
281
boot/fat32.asm
281
boot/fat32.asm
|
|
@ -1,281 +0,0 @@
|
|||
; Bootsector for FAT32 filesystems
|
||||
org 0x0800
|
||||
cpu 8086
|
||||
jmp short init
|
||||
nop
|
||||
|
||||
%include "inc/bpb.asm"
|
||||
|
||||
bpb: equ 0x080B
|
||||
|
||||
; Area for BPB
|
||||
times ( 0x5A - ($-$$) ) db 0
|
||||
|
||||
init: xor ax, ax
|
||||
mov ss, ax
|
||||
mov sp, 0x7C00
|
||||
|
||||
; save potential partition table entry
|
||||
push ds
|
||||
push si
|
||||
|
||||
mov ds, ax
|
||||
mov es, ax
|
||||
|
||||
mov si, 0x7C00
|
||||
mov di, 0x0800
|
||||
mov cx, 0x0100
|
||||
rep movsw
|
||||
jmp 0x0:main
|
||||
|
||||
%include "inc/booterr.asm"
|
||||
|
||||
; offsets relative to FS
|
||||
readd: ; add offset of cluster data area to DX:AX
|
||||
push cx
|
||||
mov di, [bp+bpb_rde]
|
||||
mov cl, 4
|
||||
shr di, cl ; 32 bytes per entry
|
||||
add ax, di
|
||||
adc dx, 0
|
||||
pop cx
|
||||
readr: ; add offset to rootdir to DX:AX (FAT12/FAT16 only)
|
||||
push cx
|
||||
xor ch, ch
|
||||
mov cl, byte [bp+bpb_fn]
|
||||
fatlp: add ax, [bp+bpb7_lsf]
|
||||
adc dx, [bp+bpb7_lsf+2]
|
||||
loop fatlp
|
||||
pop cx
|
||||
readf: ; add offset to FAT table to DX:AX
|
||||
add ax, word [bp+bpb_rsc]
|
||||
adc dx, 0
|
||||
readp: ; read sector DX:AX from partition
|
||||
add ax, word [bp+bpb_po]
|
||||
adc dx, word [bp+bpb_po+2]
|
||||
jc dskerr
|
||||
|
||||
; This jump is overwritten with NOP's if LBA support
|
||||
dskjmp: jmp rchs
|
||||
|
||||
rebios: ; read sector DX:AX from disk
|
||||
; this uses the EBIOS extensions
|
||||
; qword sector number DX:AX
|
||||
push cs
|
||||
push cs
|
||||
push dx
|
||||
push ax
|
||||
|
||||
; dword target buffer: BX:0
|
||||
push bx
|
||||
push cs
|
||||
|
||||
; word sector number
|
||||
push cx
|
||||
|
||||
; size & passing
|
||||
mov di, 0x10
|
||||
push di
|
||||
|
||||
mov si, sp
|
||||
mov ah, 0x42
|
||||
mov dl, [bp+bpb7_dn]
|
||||
stc
|
||||
int 0x13
|
||||
jc dskerr
|
||||
|
||||
add sp, di
|
||||
|
||||
ret
|
||||
|
||||
rchs: ; read sector DX:AX from disk
|
||||
; uses basic CHS disk IO
|
||||
; this cant reliable read over track boundaries
|
||||
; so we read each single sector in loop over CX
|
||||
chslp: push ax
|
||||
push cx
|
||||
push dx
|
||||
push bx
|
||||
|
||||
; calculate CHS data
|
||||
div word [bp+bpb_spt] ; ax:temp = (lba / spt)
|
||||
inc dx ; dx:sector = (lba % spt) + 1
|
||||
mov cl, dl ; sector number
|
||||
xor dx, dx
|
||||
div word [bp+bpb_nos] ; ax:cylinder = (tmp / heads)
|
||||
; dx:head = (tmp % heads)
|
||||
mov ch, al ; cylinder number
|
||||
mov dh, dl ; head number
|
||||
mov dl, [bp+bpb7_dn] ; drive number
|
||||
|
||||
; set up read buffer
|
||||
mov es, bx
|
||||
xor bx, bx
|
||||
|
||||
; call bios
|
||||
mov ax, 0x0201
|
||||
int 0x13
|
||||
jc dskerr
|
||||
|
||||
pop bx
|
||||
pop dx
|
||||
pop cx
|
||||
pop ax
|
||||
|
||||
; increment sector num + write offset
|
||||
add ax, 1
|
||||
adc dx, 0
|
||||
add bx, 0x20
|
||||
; loop on CX
|
||||
loop chslp
|
||||
ret
|
||||
|
||||
; error handling for disk errors
|
||||
dskerr: call errcll
|
||||
|
||||
next: ; Advances DX:AX to next FAT entry
|
||||
push ax
|
||||
push bx
|
||||
|
||||
; shift 2 left for dword-sized FAT entries
|
||||
; shift 9 right for sector size
|
||||
mov cl, 7
|
||||
shftl: clc
|
||||
rcr dx, 1
|
||||
rcr ax, 1
|
||||
loop shftl
|
||||
|
||||
mov bx, 0xA0
|
||||
mov cx, 1
|
||||
call readf
|
||||
|
||||
pop bx
|
||||
|
||||
; get lower part of cluster number
|
||||
pop si
|
||||
; multiply with 4
|
||||
sal si, 1
|
||||
sal si, 1
|
||||
; make sure its within sector range
|
||||
and si, 0x1FF
|
||||
add si, buf
|
||||
; load dword from FAT
|
||||
lodsw
|
||||
mov dx, [si]
|
||||
|
||||
ret
|
||||
|
||||
; reads current cluster into [dest]
|
||||
readc: ; load cluster number
|
||||
push ax
|
||||
push dx
|
||||
|
||||
; subtract the two dummy entries from FAT start
|
||||
sub ax, 2
|
||||
sbb dx, 0
|
||||
|
||||
; convert cluster number to sector number
|
||||
; this is some cheapo multiplication with 2^n
|
||||
mov cl, [bp+bpb_sc]
|
||||
l02: shr cl, 1
|
||||
jz l02e
|
||||
clc
|
||||
rcl ax, 1
|
||||
rcl dx, 1
|
||||
jmp l02
|
||||
l02e:
|
||||
; dx:ax is now sector num in data area
|
||||
mov cx, [bp+bpb_sc]
|
||||
xor ch, ch
|
||||
|
||||
call readd
|
||||
|
||||
xchg di, cx
|
||||
mov cl, 5
|
||||
sal di, cl
|
||||
add bx, di
|
||||
|
||||
pop dx
|
||||
pop ax
|
||||
|
||||
ret
|
||||
|
||||
; Load root directory
|
||||
loadr: mov ax, 2
|
||||
xor dx, dx
|
||||
jmp load
|
||||
|
||||
; Load file identified by fsattr
|
||||
; Directory data is expected at 0x07C00
|
||||
loadf: mov si, (0x7C00-0x20)
|
||||
sloop: add si, 0x20
|
||||
; check if entry is valid
|
||||
mov al, [si]
|
||||
; unallocated direntry
|
||||
test al, al
|
||||
jz fserr
|
||||
; deleted files
|
||||
cmp al, 0xE2
|
||||
je sloop
|
||||
; check attr
|
||||
mov al, [si+11]
|
||||
and al, 0x5C
|
||||
cmp al, ah
|
||||
jne sloop
|
||||
mov ax, [si+0x1A]
|
||||
mov dx, [si+0x14]
|
||||
|
||||
; Load cluster chain DX:AX to 0x07C00
|
||||
load: mov bx, 0x07C0
|
||||
lloop: call readc
|
||||
call next
|
||||
cmp word dx, 0x0FFF
|
||||
jne lloop
|
||||
ret
|
||||
|
||||
main: ; Set up BP to point to BPB
|
||||
; Relative addressing saves one instruction byte per access
|
||||
mov bp, bpb
|
||||
; Save DL contents
|
||||
mov [bp+bpb7_dn], dl
|
||||
|
||||
; EBIOS is ignored for floppies (dl < 80h)
|
||||
test dl, 0x80
|
||||
jz noebio
|
||||
|
||||
; check for EBIOS support
|
||||
mov bx, 0x55AA
|
||||
mov ah, 0x41
|
||||
; set carry to assume failure if int didnt do anything
|
||||
stc
|
||||
int 0x13
|
||||
jc noebio
|
||||
|
||||
; disable CHS routine, fall into LBA routine instead
|
||||
mov word [dskjmp], 0x9090
|
||||
|
||||
noebio: ; load root directory
|
||||
call loadr
|
||||
; search for first system directory
|
||||
mov ah, 0x14
|
||||
call loadf
|
||||
; search for first system file
|
||||
mov ah, 0x04
|
||||
call loadf
|
||||
|
||||
; restore drive number
|
||||
mov dl, [bp+bpb7_dn]
|
||||
|
||||
; restore potential partition table
|
||||
pop si
|
||||
pop ds
|
||||
|
||||
jmp 0x7C00
|
||||
|
||||
; error handling for file not found
|
||||
fserr: call errcll
|
||||
|
||||
; Padding and signature
|
||||
times (0x1FE - ($-$$)) db 0
|
||||
dw 0xAA55
|
||||
buf:
|
||||
Loading…
Reference in New Issue