527 lines
19 KiB
NASM
527 lines
19 KiB
NASM
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; ;;
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;; "BootProg" Loader v 1.5 by Alexey Frunze (c) 2000-2015 ;;
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;; 2-clause BSD license. ;;
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;; ;;
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;; ;;
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;; This is a version of boot12.asm fully ready for a 1.44MB 3"5 floppy. ;;
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;; ;;
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;; ;;
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;; How to Compile: ;;
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;; ~~~~~~~~~~~~~~~ ;;
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;; nasm flp144.asm -f bin -o flp144.bin ;;
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;; ;;
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;; ;;
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;; Features: ;;
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;; ~~~~~~~~~ ;;
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;; - FAT12 supported ;;
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;; ;;
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;; - Loads a 16-bit executable file in the MS-DOS .COM or .EXE format ;;
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;; from the root directory of a disk and transfers control to it ;;
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;; (the "ProgramName" variable holds the name of the file to be loaded) ;;
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;; ;;
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;; - Prints an error if the file isn't found or couldn't be read ;;
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;; (the "RE" message stands for "Read Error", ;;
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;; the "NF" message stands for "file Not Found") ;;
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;; and waits for a key to be pressed, then executes the Int 19h ;;
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;; instruction and lets the BIOS continue bootstrap. ;;
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;; ;;
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;; ;;
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;; Known Limitations: ;;
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;; ~~~~~~~~~~~~~~~~~~ ;;
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;; - Works only on the 1st MBR partition which must be a PRI DOS partition ;;
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;; with FAT12 (File System ID: 1) ;;
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;; ;;
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;; ;;
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;; Known Bugs: ;;
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;; ~~~~~~~~~~~ ;;
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;; - All bugs are fixed as far as I know. The boot sector has been tested ;;
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;; on the following types of diskettes: ;;
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;; - 360KB 5"25 ;;
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;; - 1.2MB 5"25 ;;
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;; - 1.44MB 3"5 ;;
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;; ;;
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;; ;;
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;; Memory Layout: ;;
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;; ~~~~~~~~~~~~~~ ;;
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;; The diagram below shows the typical memory layout. The actual location ;;
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;; of the boot sector and its stack may be lower than A0000H if the BIOS ;;
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;; reserves memory for its Extended BIOS Data Area just below A0000H and ;;
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;; reports less than 640 KB of RAM via its Int 12H function. ;;
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;; ;;
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;; physical address ;;
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;; +------------------------+ 00000H ;;
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;; | Interrupt Vector Table | ;;
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;; +------------------------+ 00400H ;;
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;; | BIOS Data Area | ;;
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;; +------------------------+ 00500H ;;
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;; | PrtScr Status / Unused | ;;
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;; +------------------------+ 00600H ;;
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;; | Loaded Image | ;;
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;; +------------------------+ nnnnnH ;;
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;; | Available Memory | ;;
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;; +------------------------+ A0000H - 512 - 2KB ;;
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;; | 2KB Boot Stack | ;;
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;; +------------------------+ A0000H - 512 ;;
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;; | Boot Sector | ;;
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;; +------------------------+ A0000H ;;
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;; | Video RAM | ;;
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;; ;;
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;; ;;
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;; Boot Image Startup (register values): ;;
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;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
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;; dl = BIOS boot drive number (e.g. 0, 80H) ;;
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;; cs:ip = program entry point ;;
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;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
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;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
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;; EXE program defaults: ds = es = 50h, other stuff depends on EXE header ;;
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;; Magic numbers: ;;
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;; si = 16381 (prime number 2**14-3) ;;
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;; di = 32749 (prime number 2**15-19) ;;
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;; bp = 65521 (prime number 2**16-15) ;;
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;; The magic numbers let the program know whether it has been loaded by ;;
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;; this boot sector or by MS-DOS, which may be handy for universal, bare- ;;
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;; metal and MS-DOS programs. ;;
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;; ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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[BITS 16]
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;;? equ 0
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ImageLoadSeg equ 60h ; <=07Fh because of "push byte ImageLoadSeg" instructions
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[SECTION .text]
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[ORG 0]
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Boot sector starts here ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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jmp short start ; MS-DOS/Windows checks for this jump
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nop
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bsOemName DB "BootProg" ; 0x03
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;;;;;;;;;;;;;;;;;;;;;
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;; BPB starts here ;;
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;;;;;;;;;;;;;;;;;;;;;
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bpbBytesPerSector DW 512 ; 0x0B
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bpbSectorsPerCluster DB 1 ; 0x0D
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bpbReservedSectors DW 1 ; 0x0E
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bpbNumberOfFATs DB 2 ; 0x10
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bpbRootEntries DW 224 ; 0x11
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bpbTotalSectors DW 2880 ; 0x13
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bpbMedia DB 0F0h ; 0x15
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bpbSectorsPerFAT DW 9 ; 0x16
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bpbSectorsPerTrack DW 18 ; 0x18
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bpbHeadsPerCylinder DW 2 ; 0x1A
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bpbHiddenSectors DD 0 ; 0x1C
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bpbTotalSectorsBig DD 0 ; 0x20
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;;;;;;;;;;;;;;;;;;;
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;; BPB ends here ;;
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;;;;;;;;;;;;;;;;;;;
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bsDriveNumber DB 0 ; 0x24
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bsUnused DB 0 ; 0x25
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bsExtBootSignature DB 29H ; 0x26
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bsSerialNumber DD 11223344h ; 0x27
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bsVolumeLabel DB "NO NAME " ; 0x2B
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bsFileSystem DB "FAT12 " ; 0x36
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Boot sector code starts here ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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start:
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cld
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; How much RAM is there? ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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int 12h ; get conventional memory size (in KBs)
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shl ax, 6 ; and convert it to 16-byte paragraphs
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Reserve memory for the boot sector and its stack ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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sub ax, 512 / 16 ; reserve 512 bytes for the boot sector code
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mov es, ax ; es:0 -> top - 512
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sub ax, 2048 / 16 ; reserve 2048 bytes for the stack
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mov ss, ax ; ss:0 -> top - 512 - 2048
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mov sp, 2048 ; 2048 bytes for the stack
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Copy ourselves to top of memory ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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mov cx, 256
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mov si, 7C00h
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xor di, di
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mov ds, di
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rep movsw
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;;;;;;;;;;;;;;;;;;;;;;
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;; Jump to the copy ;;
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;;;;;;;;;;;;;;;;;;;;;;
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push es
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push byte main
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retf
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main:
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push cs
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pop ds
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mov [bsDriveNumber], dl ; store BIOS boot drive number
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Reserve memory for the FAT12 image (6KB max) ;;
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;; and load it in its entirety ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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mov ax, [bpbBytesPerSector]
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shr ax, 4 ; ax = sector size in paragraphs
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mov cx, [bpbSectorsPerFAT] ; cx = FAT size in sectors
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mul cx ; ax = FAT size in paragraphs
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mov di, ss
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sub di, ax
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mov es, di
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xor bx, bx ; es:bx -> buffer for the FAT
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mov ax, [bpbHiddenSectors]
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mov dx, [bpbHiddenSectors+2]
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add ax, [bpbReservedSectors]
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adc dx, bx ; dx:ax = LBA
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call ReadSector
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Reserve memory for the root directory ;;
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;; and load it in its entirety ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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mov bx, ax
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mov di, dx ; save LBA to di:bx
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mov ax, 32
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mov si, [bpbRootEntries]
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mul si
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div word [bpbBytesPerSector]
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mov cx, ax ; cx = root directory size in sectors
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mov al, [bpbNumberOfFATs]
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cbw
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mul word [bpbSectorsPerFAT]
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add ax, bx
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adc dx, di ; dx:ax = LBA
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push es ; push FAT segment (2nd parameter)
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push byte ImageLoadSeg
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pop es
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xor bx, bx ; es:bx -> buffer for root directory
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call ReadSector
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add ax, cx
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adc dx, bx ; adjust LBA for cluster data
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push dx
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push ax ; push LBA for data (1st parameter)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Look for the COM/EXE file to load and run ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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mov di, bx ; es:di -> root entries array
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mov dx, si ; dx = number of root entries
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mov si, ProgramName ; ds:si -> program name
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Looks for a file/dir by its name ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Input: DS:SI -> file name (11 chars) ;;
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;; ES:DI -> root directory array ;;
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;; DX = number of root entries ;;
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;; Output: SI = cluster number ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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FindName:
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mov cx, 11
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FindNameCycle:
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cmp byte [es:di], ch
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je FindNameFailed ; end of root directory
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pusha
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repe cmpsb
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popa
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je FindNameFound
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add di, 32
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dec dx
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jnz FindNameCycle ; next root entry
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FindNameFailed:
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jmp ErrFind
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FindNameFound:
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mov si, [es:di+1Ah] ; si = cluster no.
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;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Load the entire file ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;
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ReadNextCluster:
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Reads a FAT12 cluster ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Inout: ES:BX -> buffer ;;
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;; SI = cluster no ;;
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;; Output: SI = next cluster ;;
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;; ES:BX -> next addr ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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ReadCluster:
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mov bp, sp
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lea ax, [si-2]
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xor ch, ch
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mov cl, [bpbSectorsPerCluster]
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; cx = sector count
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mul cx
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add ax, [bp]
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adc dx, [bp+1*2]
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; dx:ax = LBA
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call ReadSector
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mov ax, [bpbBytesPerSector]
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shr ax, 4 ; ax = paragraphs per sector
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mul cx ; ax = paragraphs read
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mov cx, es
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add cx, ax
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mov es, cx ; es:bx updated
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mov ax, 3
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mul si
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shr ax, 1
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xchg ax, si ; si = cluster * 3 / 2
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push ds
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mov ds, [bp+2*2] ; ds = FAT segment
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mov si, [si] ; si = next cluster
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pop ds
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jnc ReadClusterEven
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shr si, 4
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ReadClusterEven:
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and si, 0FFFh ; mask cluster value
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ReadClusterDone:
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cmp si, 0FF8h
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jc ReadNextCluster ; if not End Of File
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Type detection, .COM or .EXE? ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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push byte ImageLoadSeg
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pop ds
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mov ax, ds ; ax=ds=seg the file is loaded to
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cmp word [0], 5A4Dh ; "MZ" signature?
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je RelocateEXE ; yes, it's an EXE program
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Setup and run a .COM program ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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sub ax, 10h ; "org 100h" stuff :)
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mov es, ax
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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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push es
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push word 100h
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jmp short Run
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Relocate, setup and run a .EXE program ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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RelocateEXE:
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add ax, [08h] ; ax = image base
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mov cx, [06h] ; cx = reloc items
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mov bx, [18h] ; bx = reloc table pointer
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jcxz RelocationDone
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ReloCycle:
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mov di, [bx] ; di = item ofs
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mov dx, [bx+2] ; dx = item seg (rel)
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add dx, ax ; dx = item seg (abs)
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push ds
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mov ds, dx ; ds = dx
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add [di], ax ; fixup
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pop ds
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add bx, 4 ; point to next entry
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loop ReloCycle
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RelocationDone:
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mov bx, ax
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add bx, [0Eh]
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mov ss, bx ; ss for EXE
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mov sp, [10h] ; sp for EXE
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add ax, [16h] ; cs
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push ax
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push word [14h] ; ip
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Run:
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mov dl, [cs:bsDriveNumber] ; pass the BIOS boot drive
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Set the magic numbers so the program knows that it ;;
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;; has been loaded by this bootsector and not by MS-DOS ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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mov si, 16381 ; prime number 2**14-3
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mov di, 32749 ; prime number 2**15-19
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mov bp, 65521 ; prime number 2**16-15
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; All done, transfer control to the program now ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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retf
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Reads a sector using BIOS Int 13h fn 2 ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Input: DX:AX = LBA ;;
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;; CX = sector count ;;
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;; ES:BX -> buffer address ;;
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;; Output: CF = 1 if error ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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ReadSector:
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pusha
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ReadSectorNext:
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mov di, 5 ; attempts to read
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ReadSectorRetry:
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pusha
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div word [bpbSectorsPerTrack]
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; ax = LBA / SPT
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; dx = LBA % SPT = sector - 1
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mov cx, dx
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inc cx
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; cx = sector no.
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xor dx, dx
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div word [bpbHeadsPerCylinder]
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; ax = (LBA / SPT) / HPC = cylinder
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; dx = (LBA / SPT) % HPC = head
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mov ch, al
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; ch = LSB 0...7 of cylinder no.
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shl ah, 6
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or cl, ah
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; cl = MSB 8...9 of cylinder no. + sector no.
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mov dh, dl
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; dh = head no.
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mov dl, [bsDriveNumber]
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; dl = drive no.
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mov ax, 201h
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; al = sector count = 1
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; ah = 2 = read function no.
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int 13h ; read sectors
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jnc ReadSectorDone ; CF = 0 if no error
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xor ah, ah ; ah = 0 = reset function
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int 13h ; reset drive
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popa
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dec di
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jnz ReadSectorRetry ; extra attempt
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jmp short ErrRead
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ReadSectorDone:
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popa
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dec cx
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jz ReadSectorDone2 ; last sector
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add bx, [bpbBytesPerSector] ; adjust offset for next sector
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add ax, 1
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adc dx, 0 ; adjust LBA for next sector
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jmp short ReadSectorNext
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ReadSectorDone2:
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popa
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ret
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;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Error Messaging Code ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;
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ErrRead:
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mov si, MsgErrRead
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jmp short Error
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ErrFind:
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mov si, MsgErrFind
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Error:
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mov ah, 0Eh
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mov bx, 7
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lodsb
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int 10h ; 1st char
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lodsb
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int 10h ; 2nd char
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xor ah, ah
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int 16h ; wait for a key...
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mov dl, [bsDriveNumber] ; restore BIOS boot drive number
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int 19h ; bootstrap
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;;;;;;;;;;;;;;;;;;;;;;
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;; String constants ;;
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;;;;;;;;;;;;;;;;;;;;;;
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MsgErrRead db "RE"
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MsgErrFind db "NF"
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Fill free space with zeroes ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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times (512-13-($-$$)) db 0
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Name of the file to load and run ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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ProgramName db "FORTH COM" ; name and extension each must be
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; padded with spaces (11 bytes total)
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;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; End of the sector ID ;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;
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dw 0AA55h ; BIOS checks for this ID
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