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Code: Select all

some_label  DB 45h

   mov si,OFFSET some_label
   mov al,cs:[si]
   mov al,cs:[some_label]

Code: Select all

%define store_location 0x1000
%define drive 0x80
%define code_sector_location 2 ;This is index 0 so we are actually pointing to sector 1.

bits 16
org 0x7c00

jmp start

start:

	mov ax, cs	;AX points to CS 0x7c0
	mov ds, ax	;DS points to 0x7c0
	mov es, ax	;ES contains what is on 0x7c0

	mov al, 03h	;Text mode 25x80
	mov ah, 0
	int 10h
	
	mov ax, store_location
	mov es, ax	;Point ES to store_location (top of our stack)
	mov cl, code_sector_location
	mov al, 3	;Number of sectors to read

	call read_sectors	;Load sectors and put them into RAM address of store_location

	jmp store_location:0000	;Far jump to offset 0000 to the segment in RAM where we have stored our program code after reading from it disk
	
	
read_sectors:
	mov bx, 0
	mov dl, drive
	mov dh, 0	;Head to read
	mov ch, 0	;Track to read
	mov ah, 2	;To read sectors
	int 0x13
	jc error_reading
	ret
	error_reading:
		mov si, error_msg
		call print
		mov ah, 0	;Wait for key press
		int 16h
		int 19h		;Reboot but leave memory to where is pointing

print:
	pusha	;Store all general-purpose registers on the stack
	mov bp, sp	;Allocates in stack program variables
	iterate:
		lodsb	;Loads 8bit byte address to work with strings
		or al, al	;Logic or to check if string already reached its end "0"
		jz done_writing
		mov ah, 0x0e	;To print character into screen
		mov bx, 0
		int 10h
		jmp iterate
	done_writing:
		mov sp, bp	;Get variables out of stack
		popa		;Retrieve all general-purpose registers of the stack with order LIFO ignoring SP
		ret

error_msg db "An error occurred while reading sectors and loading them into RAM ", 10, 13, 0

times 510 - ($-$$) db 0
dw 0xaa55

Code: Select all

[bits 16]
[org 0]

start:
	mov ax, cs ;AX points to CS (0)
	mov ds, ax ;Data segment is now pointing to (0)
	mov es, ax ;ES points to (0) too

	
mov si, A
call print
mov si, B
call print
mov si, C
call print
mov si, D
call print
mov si, E
call print
mov si, F
call print
mov si, G
call print
mov si, H
call print
mov si, I
call print
mov si, J
call print
mov si, K
call print
mov si, L
call print
mov si, M
call print
mov si, N
call print
mov si, O
call print
mov si, P
call print
mov si, Q
call print


mov ah, 0	;Wait for key press
int 16h
int 19h		;Reboot but leave memory to where is pointing so we can continue with our normal boot

print:
	pusha	;Store all general-purpose registers on the stack
	mov bp, sp	;Allocates in stack program variables
	iterate:
		lodsb	;Loads 8bit byte address from SI register to work with strings
		or al, al	;Logic or to check if string already reached its end "0"
		jz done_writing
		mov ah, 0x0e	;To print character into screen
		mov bx, 0
		int 10h
		jmp iterate
	done_writing:
		mov sp, bp	;Get variables out of stack
		popa		;Retrieve all general-purpose registers of the stack with order LIFO ignoring SP
		ret 

A db    "           ___     ___     ___     ___     ___     ___     ___     ___ ", 10,13,0
B db    "       ___/   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \___", 10,13,0
C db    "      /   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \ ", 10,13,0
D db    "      \___/   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \___/ ", 10,13,0
E db    "      /   \___/                                                   \___/   \ ", 10,13,0
F db    "      \___/                                                           \___/ ", 10,13,0
G db    "      /   \                                                           /   \ ", 10,13,0
H db    "      \___/                Welcome to my bootloader!                  \___/ ", 10,13,0
I db    "      /   \                   Under construction                      /   \ ", 10,13,0
J db    "      \___/                                                           \___/", 10,13,0
K db    "      /   \                Press any key to continue                  /   \ ", 10,13,0
L db    "      \___/                   with normal boot.                       \___/ ", 10,13,0
M db    "      /   \___                                                     ___/   \ ", 10,13,0
N db    "      \___/   \___     ___     ___     ___     ___     ___     ___/   \___/ ", 10,13,0
O db    "      /   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \ ", 10,13,0
P db    "      \___/   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \___/ ", 10,13,0
Q db    "          \___/   \___/   \___/   \___/   \___/   \___/   \___/   \___/ ", 10,13,0

Code: Select all

%define store_location 0x1000
%define drive 0x80
%define code_sector_location 1 ;This is index 0 so we are actually pointing to sector 1.

bits 16
org 0x7c00

jmp start

start:

   mov ax, cs   ;AX points to CS 0x7c0
   mov ds, ax   ;DS points to 0x7c0
   mov es, ax   ;ES contains what is on 0x7c0

   mov al, 03h   ;Text mode 25x80
   mov ah, 0
   int 10h
   
   mov ax, store_location
   mov ds, ax	;We will print our read sector from DS:SI so we need DS to point to the correct location
   mov es, ax   ;Point ES to store_location (top of our stack)
   mov cl, code_sector_location
   mov al, 1   ;Number of sectors to read

   call read_sectors   ;Load sectors and put them into RAM address of store_location
 
   
   mov si, 0           ;ds:si = address of first byte of loaded sector
   mov cx, 8           ;cx = number of lines to dump to screen (64 bytes per line * 8 lines = 512 bytes). The loop will execute 8 times

read_sectors:
   mov bx, 0
   mov dl, drive
   mov dh, 0   ;Head to read
   mov ch, 0   ;Track to read
   mov ah, 2   ;To read sectors
   int 0x13
   jc error_reading
   ret
   error_reading:
      mov si, error_msg
      call print
      mov ah, 0   ;Wait for key press
      int 16h
      int 19h      ;Reboot but leave memory to where is pointing   
   
print_line:
    call print_data
    loop print_line
	
	mov ah, 0   ;Wait for key press
      int 16h
      int 19h      ;Reboot but leave memory to where is pointing
	
print_data:
    push cx					;Store cx current value so we can still count the lines to print when we get out of our next loop of printing 64 characters
    mov cx,64               ;Loop 64 times
    cld						;Clear direction flag to read DS:SI string from left to right.
next_char:
    lodsb
	cmp al, ' '              ;Can the byte be displayed as ACSII?
    jbe .badChar            ; no, too low or space, use '.' instead
    cmp al, 0x7F             ;Can the byte be displayed as ACSII?
    jb .doChar              ; yes
                            ; no, too high or delete, use '.' instead
.badChar:
    mov al,'.'
.doChar:
    mov ah,0x0E
    int 0x10
    loop next_char
done:
    mov ax, 0x0E0A           ;Newline
    int 0x10
    mov ax, 0x0E0D           ;Carriage return
    int 0x10

    pop cx
    ret

print:
   pusha   ;Store all general-purpose registers on the stack
   mov bp, sp   ;Allocates in stack program variables
   iterate:
      lodsb   ;Loads 8bit byte address to work with strings
      or al, al   ;Logic or to check if string already reached its end "0"
      jz done_writing
      mov ah, 0x0e   ;To print character into screen
      mov bx, 0
      int 10h
      jmp iterate
   done_writing:
      mov sp, bp   ;Get variables out of stack
      popa      ;Retrieve all general-purpose registers of the stack with order LIFO ignoring SP
      ret

error_msg db "An error occurred while reading sectors and loading them into RAM ", 10, 13, 0

times 510 - ($-$$) db 0
dw 0xaa55