bits 16 org 0x500 jmp main ; Global Descriptor Table gdt: dd 0 dd 0 dw 0xffff dw 0 db 0 db 10011010b db 11001111b db 0 dw 0xffff dw 0 db 0 db 10010010b db 11001111b db 0 gdt_descriptor: dw gdt_descriptor - gdt - 1 dd gdt ; Data BytesPerSector dw 512 RootEntries dw 224 SectorsPerTrack dw 18 HeadsPerCylinder dw 2 DriveNumber db 0xFF filename db "KERNEL BIN" filesize dd 0 err_notfound db "ERROR: Kernel file not found", 13, 10, 0 err_floppy db "ERROR: Floppy disk failure", 13, 10, 0 cluster dw 0 pointer dw 0 msg_ax db "AX:", 0 msg_bx db "BX:", 0 msg_cx db "CX:", 0 msg_dx db "DX:", 0 msg_sp db "SP:", 0 msg_bp db "BP:", 0 msg_si db "SI:", 0 msg_di db "DI:", 0 msg_ip db "IP:", 0 msg_es db "ES:", 0 msg_cs db "CS:", 0 msg_ss db "SS:", 0 msg_ds db "DS:", 0 msg_fs db "FS:", 0 msg_gs db "GS:", 0 msg_tab db " ", 0 msg_nl db 13, 10, 0 ; Code main: ; Setting up registers cli xor ax, ax mov ds, ax mov es, ax mov ax, 0x9000 mov ss, ax mov sp, 0xffff sti ; Loading the GDT lgdt [gdt_descriptor] ; Enable A20 in al, 0x92 test al, 2 jnz a20ok or al, 2 and al, 0xfe out 0x92, al a20ok: cmp dl, [DriveNumber] je drive_number_ok mov [DriveNumber], dl mov ah, 8 push ax push bx push cx push dx push es push di pushf int 0x13 popf pop di pop es pop dx pop cx pop bx pop ax jmp ent_pmode ; SKIPPING EVERTHING BELOW jc fatal_disk_error and cx, 0x3f mov [SectorsPerTrack], cx movzx dx, dh add dx, 1 mov [HeadsPerCylinder], dx drive_number_ok: mov eax, 0 floppy_ok: mov ax, 19 ; NumberOfFATs * SectorsPerFAT + ReservedSectors call l2hts mov si, buffer mov bx, ds mov es, bx mov bx, si mov ah, 0x2 ; Param for int 0x13: read floppy sectors mov al, 14 ; Read 14 of them pusha read_root_dir: popa pusha stc int 0x13 jnc search_dir ; If OK, skip ahead call reset_floppy ; Else, reset the floppy controller and try again jnc read_root_dir ; Floppy reset OK? jmp fatal_disk_error ; If not, fatal double error search_dir: popa mov ax, ds ; Root dir is now in [0x2e00] mov es, ax ; Set DI to this info mov di, buffer mov cx, word [RootEntries] mov ax, 0 next_root_entry: xchg cx, dx ; We use 'cx' in the inner loop mov si, filename mov cx, 11 rep cmpsb je found_file_to_load add ax, 32 mov di, buffer add di, ax xchg dx, cx ; loop next_root_entry dec cx jnz next_root_entry mov si, err_notfound call print_string16 jmp reboot found_file_to_load: mov ax, word [es:di + 0xF] ; Offset 11 + 15 = 26 mov word [cluster], ax mov ax, 1 ; Sector 1 call l2hts mov di, buffer mov bx, di mov ah, 0x2 ; int 0x13 parameters: read (FAT) sectors mov al, 9 ; all 9 sectors of first FAT pusha read_fat: popa pusha stc int 0x13 jnc read_fat_ok ; If it went OK, skip ahead call reset_floppy ; Else, reset floppy controller and try again jnc read_fat ; Floppy reset OK? fatal_disk_error: mov si, err_floppy ; If not, print message and reboot call print_string16 jmp reboot ; FATAL DOUBLE ERROR read_fat_ok: popa mov ax, 0x3000 ; Where we'll load the boot1 stage mov es, ax mov bx, 0x0000 mov ah, 0x2 ; int 0x13 parameters: read floppy mov al, 1 xor ecx, ecx push ecx push ax load_file_sector: mov ax, word [cluster] add ax, 31 call l2hts mov ax, 0x3000 mov es, ax mov bx, word [pointer] pop ax push ax stc int 0x13 jnc calculate_next_cluster ; If there's no error call reset_floppy ; Else, reset floppy and try again jmp load_file_sector calculate_next_cluster: pop ax pop ecx inc ecx push ecx push ax mov ax, [cluster] mov dx, 0 mov bx, 3 mul bx mov bx, 2 div bx ; 'dx' = [cluster] mod 2 mov si, buffer add si, ax ; 'ax' = word in FAT for the 12 bit entry mov ax, word[ds:si] or dx, dx jz even ; If [cluster] is even, drop last 4 bits of word ; with next cluster; if odd, drop first 4 bits odd: shr ax, 4 ; Shift out first 4 bits jmp short next_cluster_cont even: and ax, 0xfff ; Mask out last 4 bits next_cluster_cont: mov word [cluster], ax cmp ax, 0xff8 jae end add word [pointer], 512 jmp load_file_sector end: pop ax pop ecx mov dword [filesize], ecx ent_pmode: ; Clear the screen push ax mov ah, 0 mov al, 3 int 0x10 pop ax ; Print the segments push si mov si, msg_ax call print_string16 push ax call print_hex_word pop ax mov si, msg_tab call print_string16 mov si, msg_bx call print_string16 push bx call print_hex_word pop bx mov si, msg_tab call print_string16 mov si, msg_cx call print_string16 push cx call print_hex_word pop cx mov si, msg_nl call print_string16 mov si, msg_dx call print_string16 push dx call print_hex_word pop dx mov si, msg_tab call print_string16 mov si, msg_sp call print_string16 push sp call print_hex_word pop sp mov si, msg_tab call print_string16 mov si, msg_bp call print_string16 push bp call print_hex_word pop bp mov si, msg_nl call print_string16 mov si, msg_si call print_string16 call print_hex_word pop si mov si, msg_tab call print_string16 mov si, msg_di call print_string16 push di call print_hex_word pop di mov si, msg_tab call print_string16 mov si, msg_ip call print_string16 push word buffer call print_hex_word pop si mov si, msg_nl call print_string16 mov si, msg_es call print_string16 push es call print_hex_word pop es mov si, msg_tab call print_string16 mov si, msg_cs call print_string16 push cs call print_hex_word pop ax mov si, msg_tab call print_string16 mov si, msg_ss call print_string16 push ss call print_hex_word pop ss mov si, msg_nl call print_string16 mov si, msg_ds call print_string16 push ds call print_hex_word pop ds mov si, msg_tab call print_string16 mov si, msg_fs call print_string16 push fs call print_hex_word pop fs mov si, msg_tab call print_string16 mov si, msg_gs call print_string16 push gs call print_hex_word pop gs ; Wait for a keystroke mov ax, 0 int 0x16 ; Entering protected mode cli mov eax, cr0 or eax, 1 mov cr0, eax jmp 0x8:pmain ; COMPUTER REBOOTS AFTER THIS INSTRUCTION cli hlt ; Reset floppy controller reset_floppy: push ax push dx mov ax, 0 mov dl, 0 stc int 0x13 pop dx pop ax ret ; Reboot reboot: mov ah, 0 int 0x16 ; Wait for keystroke cli int 0x19 ; Reboot ; Logical to head track sector ; IN: ax(logical sector); OUT: correct registers for int 13 l2hts: push bx push ax mov bx, ax mov dx, 0 div word [SectorsPerTrack] add dl, 1 mov cl, dl mov ax, bx mov dx, 0 div word [SectorsPerTrack] mov dx, 0 div word [HeadsPerCylinder] mov dh, dl mov ch, al mov dl, byte [DriveNumber] pop ax pop bx ret ; Print String ; IN: si(string location; OUT: print_string16: mov ah, 0xe .loop: lodsb or al, al jz .done int 0x10 jmp .loop .done: ret ; Print HEX value print_hex_word: pusha ; Save all registers, 16 bytes total mov bp, sp ; BP=SP, on 8086 can't use sp in memory operand mov cx, 0x0404 ; CH = number of nibbles to process = 4 (4*4=16 bits) ; CL = Number of bits to rotate each iteration = 4 (a nibble) mov dx, [bp+18] ; DX = word parameter on stack at [bp+18] to print mov bx, 13 ; BX = page / foreground attr is at [bp+20] .loop: rol dx, cl ; Roll 4 bits left. Lower nibble is value to print mov ax, 0x0e0f ; AH=0E (BIOS tty print),AL=mask to get lower nibble and al, dl ; AL=copy of lower nibble add al, 0x90 ; Work as if we are packed BCD daa ; Decimal adjust after add. ; If nibble in AL was between 0 and 9, then CF=0 and ; AL=0x90 to 0x99 ; If nibble in AL was between A and F, then CF=1 and ; AL=0x00 to 0x05 adc al, 0x40 ; AL=0xD0 to 0xD9 ; or AL=0x41 to 0x46 daa ; AL=0x30 to 0x39 (ASCII '0' to '9') ; or AL=0x41 to 0x46 (ASCII 'A' to 'F') int 0x10 ; Print ASCII character in AL dec ch jnz .loop ; Go back if more nibbles to process popa ; Restore all the registers ret ; Protected mode code bits 32 %include "vga.inc" msg_p db "Hey! It works!", 10, 0 pmain: mov ax, 0x10 mov ds, ax mov ss, ax mov es, ax mov esp, 0x90000 call clear_screen mov ebx, msg_p call print_string cli hlt mov eax, dword [filesize] movzx ebx, word [BytesPerSector] mul ebx mov ebx, 4 div ebx cld mov esi, 0x30000 mov edi, 0x100000 mov ecx, eax rep movsd call 0x8:0x100000 cli hlt buffer: