Implement boot based on reserved sectors
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parent
74fce7191f
commit
47630b2c03
11
Makefile
11
Makefile
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@ -2,8 +2,11 @@ FLOPPY = 360
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RAM = 0x10000
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BDOSIMG = bdos.bin
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BIOSIMG = bios8086.bin
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PROGRAMS = $(patsubst %.asm,%.com,$(wildcard com/*.asm))
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DISTFILES = bdos.bin $(PROGRAMS)
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DISTFILES = $(PROGRAMS)
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ROMS =
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QEMU_ARCH = $(shell uname -m)
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@ -52,8 +55,10 @@ com/%.com: com/%.asm
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bios%.bin: bios/%.asm
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$(NASM) $(NASM_ARGS) -o $@ $<
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fdimage.img: boot/fat.bs $(DISTFILES)
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mformat -C -i $@ -f $(FLOPPY) -B boot/fat.bs ::
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fdimage.img: boot/fat.bs $(BDOSIMG) $(BIOSIMG) $(DISTFILES)
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mformat -R 9 -C -i $@ -f $(FLOPPY) -B boot/fat.bs ::
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dd if=$(BDOSIMG) bs=512 seek=1 count=4 conv=notrunc of=$@
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dd if=$(BIOSIMG) bs=512 seek=5 count=4 conv=notrunc of=$@
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mcopy -i $@ $(DISTFILES) ::
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hdimage.img: boot/mbr.bs fdimage.img
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@ -23,13 +23,12 @@ JMP NEAR WRITE
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JMP NEAR LISTST
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BOOT:
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MOV AL, 0x19
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MOV AL, 0x86
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CALL MSG
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DB "BIOS 8086", 0
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RET
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DB "BIOS", 0
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WBOOT:
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STC
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JMP (RAM - 0x1000)
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RET
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; CHAR I/O
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140
boot/fat.asm
140
boot/fat.asm
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@ -1,18 +1,11 @@
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; Memory layout:
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%define segment 0x00100
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%define self (0x7C00-(segment<<4)) ; 1 sector
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%define fattab (self+0x200) ; variable size
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%define rootdir 0x00100 ; variable size
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%define prog 0x0F000 ; 4K at the end for OS
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%define prog (RAM-0x1000) ; 4K at the end for OS
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cpu 8086
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org self
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jmp short init
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cluster_offset:
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dw 0
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times (0x0B - ($-$$)) db 0
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fdc:
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@ -70,122 +63,11 @@ main:
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mov es, ax
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mov [fdc.drv], dl ; save drive number in fd
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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, fattab
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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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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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; 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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mov bx, rootdir
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call load_sectors
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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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; Load kernel
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mov ax, 1
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mov cx, 8
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mov dx, 0
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mov bx, prog
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mov ax, kernel_name
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call load_file
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mov bp, 0x3332
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jc error
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mov dl, [fdc.drv]
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; jump into kernel
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jmp segment:prog
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; Load a file into memory
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; IN AX pointer to 8.3 filename
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; ES:BX pointer to target area
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; OUT CF flag set if error
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; DI file size in bytes (<64K)
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load_file:
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mov si, rootdir
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mov cx, [fdc.rde]
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.search:
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push cx
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push si
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mov di, ax
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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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je .read
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add si, 0x20
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loop .search
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xor di, di
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stc
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ret
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.read:
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mov ax, [si+0x1A]
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mov di, [si+0x1C]
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jmp read_clusters
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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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; 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, fattab
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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 read_clusters
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ret
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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, 0x3330
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jnz error
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.loop:
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push ax
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@ -217,10 +99,15 @@ load_sectors:
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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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add ax, 1
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adc dx, 0
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loop .loop
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ret
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mov dl, [fdc.drv]
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; jump into kernel
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jmp segment:(prog+0x0800)
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error:
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mov ax, bp
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@ -233,9 +120,6 @@ error:
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int 0x16
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int 0x19
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kernel_name:
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db "BDOS BIN"
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times (0x1FE - ($-$$)) db 0
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dw 0xAA55
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