example_boot_sector

org 0x7c00				; Tell assembler to correct the offsets

;
;	Main method
;	Prints welcome and exit messages
;

;mov bx, HELLO_MSG
;call PRINT_NWLN
;
mov bx, PRINTING_HEX_MSG_1
call PRINT

mov dx, 0x1fb6
call PRINT_HEX_NWLN

mov bx, PRINTING_HEX_MSG_2
call PRINT

mov dx, 0xdead
call PRINT_HEX_NWLN
;
;mov ax, 0x4000
;mov bx, 0
;mov es, ax
;mov dh, 2
;call READ_DISK
;
;mov bx, GOODBYE_MSG
;call PRINT

jmp $					; Hang

;
;	Print Newline
;	Wrapper for print function
;	Appends newline
;

PRINT_NWLN:
	call PRINT
	push bx
	mov bx, NWLN
	call PRINT
	pop bx
	ret

;
;	Print function
;	Takes parameters via bx
;	Returns nothing
;	Preserves registers
;
;	Prints out the null terminated
;	string stored at address in bx
;

PRINT:
	pusha
	mov ah, 0x0e			; scrolling teletype bios routine
.eval_char:
	mov cx, [bx]
	test cl, cl				; check to see if string has terminated
	je .done
	mov al, cl
	int 0x10				; interrupt prints to screen
	add bx, 1				; move to the next character
	jmp .eval_char
.done:
	popa
	ret

;
;	Wrapper for PrintHex
;	Appends newline
;

PRINT_HEX_NWLN:
	call PRINT_HEX
	push bx
	mov bx, NWLN
	call PRINT
	pop bx
	ret

;
;	PrintHex function
;	Takes parameters via dx
;	Returns nothing
;	Preserves registers
;	Uses global HEX_VALUE
;	
;	Prints out the hexidecimal 
;	stored in the dx register
;

PRINT_HEX:
	pusha				; setup registers
	mov ax, 0xf000
	mov cl, 12
	mov bx, HEX_VALUE
	add bx, 2
.adjust_hex_value:
	push dx				; save original value for later use
	and dx, ax			; isolate four appropriate bits
	shr dx, cl
	cmp dx, 0xa
	jl .was_just_digit
	add dx, 39			; some number voodoo for ascii
.was_just_digit:
	add [bx], dx		; edit character the bytes in bx represent
	shr ax, 4			; increment to next bits
	sub cl, 4
	add bx, 1
	pop dx
	test ax, ax
	jne .adjust_hex_value
	mov bx, HEX_VALUE
	call PRINT
    mov bx, HEX_VALUE
    add bx, 2
	mov cx, '0'
	mov [bx], cx
	add bx, 1
	mov [bx], cx
	add bx, 1
	mov [bx], cx
	add bx, 1
	mov [bx], cx
	add bx, 1
	popa
	ret

HEX_VALUE:
	db '0x0000',0

;
;	ReadDisk option
;	Takes number of sectors to read via dh
;	Returns nothing
;	Does not preserve registers
;	Reads in a number of sectors from
;	the boot medium, immediately following
;	the boot sector itself
;	Loads the sectors to ES:BX
;
;
;READ_DISK:
;
;	push bx					; inform user of disk read
;	mov bx, DISK_LOADING_MSG
;	call PRINT_NWLN
;	pop bx
;
;	push dx
;	mov ah, 0x02			; BIOS read sector function
;	mov al, dh				; reads DH sectors
;	mov ch, 0x00			; cylinder 0
;	mov dh, 0x00			; head 0
;	mov cl, 0x02			; sector 2
;
;	int 0x013
;
;	jc .disk_error			; if carry flag set, jump to error handler
;
;	pop dx					; restore original dx
;	cmp dh, al				; if sectors read != sectors requested:
;	jne .disk_error			;	jump to error handler
;	
;	mov bx, DISK_SUCCESS_MSG
;	call PRINT_NWLN
;
;	ret
;.disk_error:
;	mov bx, DISK_ERROR_MSG_1	; inform user of failure
;	call PRINT
;	mov bh, 0
;	mov bl, al
;	call PRINT_HEX
;	mov bx, DISK_ERROR_MSG_2
;	call PRINT_NWLN
;	jmp $						; Hang on error
;
;
;	Globals
;

NWLN:
	db 0xa,0xd,0

PRINTING_HEX_MSG_1:
	db 'Currently printing a hex number...Should be 0x1fb6: ',0

PRINTING_HEX_MSG_2:
	db 'Currently printing a hex number...Should be 0x9c1a: ',0

;DISK_LOADING_MSG:
;	db 'Reading sectors from disk...',0
;
;DISK_ERROR_MSG_1:
;	db 'Disk read error!',0xa,0xd,'Read failed after ',0
;
;DISK_ERROR_MSG_2:
;	db ' sectors were read',0
;
;DISK_SUCCESS_MSG:
;	db 'Sectors read to memory',0
;
;HELLO_MSG:
;	db 'Salutations. Welcome to NimbOS.',0
;
;GOODBYE_MSG:
;	db 'Farewell. Until next time.',0
;
;
;	Magic number and padding
;

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

;
;	Added a byte of gibberish to read from
;

times 256 dw 0xabab
times 256 dw 0xcdcd