vbr: implement file searching in rootdir
This commit is contained in:
parent
cb3c977286
commit
97fe07a210
180
boot/vbr.asm
180
boot/vbr.asm
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@ -1,4 +1,4 @@
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org 0
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org 0x0500
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fdc: ; FDC Descriptor as per ECMA-107
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jmp _startup
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@ -47,23 +47,21 @@ _startup:
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xor ax, ax
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mov ds, ax
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mov es, ax
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mov ss, ax
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xor sp, sp
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mov cx, 0x0100
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mov si, 0x7C00
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mov di, 0x0500
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rep movsw
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jmp 0x0050:.lowstart
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.lowstart:
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mov ax, cs
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mov ds, ax
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mov ss, ax
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xor sp, sp
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rep movsw ; relocate
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jmp 0x0000:main
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main:
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mov [fdc.drv], dl ; backup drive number
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chs_bios:
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adjustchs:
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mov ah, 0x08
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int 0x13 ; required, QEMU detects 360kB as 1200kB with CHS 80 2 15
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jc chs_print ; skip if function does not exist
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jc loaddir ; skip if function does not exist
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inc dh
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mov [fdc.nos], dh
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mov ax, cx
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@ -77,72 +75,54 @@ chs_bios:
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mul word [fdc.nos] ; number of tracks = number of cylinders * heads
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mul word [fdc.spt] ; number of sectors = number of tracks * sectors per track
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mov [fdc.ts], ax
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jmp chs_print
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chs_print:
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call print_inline
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db "CHS ", 0
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mov ax, [fdc.ts]
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div word [fdc.nos]
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div word [fdc.spt]
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call print_number
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call print_inline
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db ",", 0
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mov ax, [fdc.nos]
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call print_number
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call print_inline
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db ",", 0
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mov ax, [fdc.spt]
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call print_number
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call print_inline
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db 0x0A, 0x0D, 0
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mov ax, 0x0070
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mov es, ax
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xor bx, bx
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call loadrootdir
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call dump
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.end:
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hlt
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jmp .end
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; Load root directory into memory
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; in es data segment
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loadrootdir:
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push bx
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push cx
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mov bx, [fdc.ss] ; bytes per sector
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loaddir:
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mov bx, [fdc.ss] ; bytes per sector
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mov cl, 5
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shr bx, cl ; div by 2^5, 32 bytes per directory entity
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mov ax, [fdc.rde] ; number of root directory entities
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shr bx, cl ; div by 2^5, 32 bytes per directory entity
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mov ax, [fdc.rde] ; number of root directory entities
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xor dx, dx
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div bx
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mov cx, ax
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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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xor bx, bx ; load at beginning of es
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mov cx, ax ; cx = number of rootdir sectors
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mov ax, [fdc.sf] ; sectors per fat
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mul byte [fdc.fn] ; number of fats
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add ax, [fdc.rsc] ; ax = starting sector of rootdir
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mov bx, buffer
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.loop:
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call loadblk
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add bx, buffer
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add ax, 1
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loop .loop
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scandir:
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mov cx, [fdc.rde]
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mov bx, buffer
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.loop:
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push cx
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mov cx, 0x000B
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mov si, bx
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mov di, bootfilename
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repe cmpsb
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pop cx
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pop bx
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ret
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jz found
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add bx, 0x0020 ; 32 bytes per directory entry
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loop .loop
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call print_inline
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db "File not found", 0x0A, 0x0D, 0
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jmp hlt
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found:
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add bx, 26
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mov ax, [bx]
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call print16
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jmp hlt
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hlt:
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hlt
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jmp hlt
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; Load a single block into memory
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; in ax sector number
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; es:bx buffer
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; bx buffer
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; out al error code,
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; carry set if error
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loadblk:
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@ -165,79 +145,41 @@ loadblk:
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pop dx
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pop cx
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pop ax
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inc ax
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add bx, 0x0200
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ret
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.error:
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xor al, al
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xchg al, ah
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call print_inline
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db "disk error ", 0
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call print_number
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call print8
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call print_inline
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db 0x0A, 0x0D, 0
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.hlt:
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hlt
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jmp .hlt
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print_number:
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mov cx, 0x000A
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xor dx, dx
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div cx ; ax = dx:ax / 10, dx = dx:ax % 10
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and ax, ax
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jz .print
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push dx
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call print_number
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pop dx
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.print:
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mov al, dl
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add al, 0x30
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mov ah, 0x0e
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int 0x10
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ret
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print_inline:
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pop si
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push ax
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push bx
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.loop:
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lodsb
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cmp al, 0x00
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je .end
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mov bx, 0x0000
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mov ah, 0x0e
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int 0x10
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cmp al, 0x0D
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jmp .loop
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.end:
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pop bx
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pop ax
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push si
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ret
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jmp hlt
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; in si
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dump:
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mov si, bx
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mov cx, 0x10
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.nextline:
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mov ax, si
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call print16
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mov al, 0x3A
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call printc
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mov al, 0x20
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call printc
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push si
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call print_inline
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db 0x3A, 0x20, 0
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pop si
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push cx
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mov cx, 0x0020
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.words:
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es lodsb
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.bytes:
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lodsb
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call print8
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loop .words
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loop .bytes
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pop cx
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mov al, 0x0A
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call printc
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mov al, 0x0D
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call printc
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push si
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call print_inline
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db 0x0A, 0x0D, 0
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pop si
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loop .nextline
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@ -247,7 +189,7 @@ dump:
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times (0x1F0 - ($-$$)) db 0
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str_bootfile:
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bootfilename:
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db "BOOT"
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times (0x1F8 - ($-$$)) db " "
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db "BIN"
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@ -255,3 +197,5 @@ str_bootfile:
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times (0x1FE - ($-$$)) db 0
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dw 0xAA55
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buffer:
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@ -0,0 +1,66 @@
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; important functions in this file: kprintf
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; write a character to kernel output
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; in: al
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printc:
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push ax
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push bx
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mov bx, 0x0000
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mov ah, 0x0e
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int 0x10
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pop bx
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pop ax
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ret
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; prints a nibble in hex
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; in: al
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print4:
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and al, 0x0F
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add al, 0x30
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cmp al, 0x3a
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jl printc
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add al, 0x07
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jmp printc
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; print a byte
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; in: al
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print8:
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push ax ; avoid destroying ah
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aam 16 ; high nibble moved into ah
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xchg ah,al ; high nibble first
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call print4
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xchg ah,al
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call print4
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pop ax
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ret
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; print a word
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; in: ax
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print16:
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xchg ah,al
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call print8
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xchg ah,al
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call print8
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ret
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; print a inline following its call opcode
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; the string ends with a nullbyte
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; trashes si
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print_inline:
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pop si
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push ax
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push bx
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mov bx, 0x0000
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.loop:
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lodsb
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cmp al, 0x00
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je .end
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mov ah, 0x0e
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int 0x10
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cmp al, 0x0D
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jmp .loop
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.end:
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pop bx
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pop ax
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push si
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ret
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