ORG 0x7C00
BITS 16
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Bootloader for SingOS
; version 0.1.0.10-exp
;
; Please edit the version number if any changes is made, the last number
; represent the build number. 
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    cli
    jmp long 0x0000:start

start:
    xor ax, ax
    mov ds, ax
    mov es, ax
    mov ss, ax
    mov [disk_identifier], dl

    ; initialize stack
    ; Set up 4K stack after this bootloader
    ; [Remember: Effective Address = Segment*16 + Offset]
    mov ax, 0x7C0   ; Set 'ax' equal to the location of this bootloader divided by 16
    add ax, 0x20     ; Skip over the size of the bootloader divided by 16
    mov ss, ax      ; Set 'ss' to this location (the beginning of our stack region)
    mov sp, 8192    ; Set 'ss:sp' to the top of our 8K stack
    sti
	mov si, message ; Put address of the null-terminated string to output into 'si'
	call print      ; Call our string-printing routine

	mov si, enter_debug_mode
    call print 
    call printCRLF
    %IF 0
    ; here goes wait call, for the user to enter debug mode. 
    ; Wating for 2 seconds: 
    mov ah, 0x86   ; code for waiting interupt call
    mov cx, 0x001e ; high count of microseconds
    mov dx, 0x8480 ; low count
    int 0x15

    .busy_wait_for_key:
    xor ax, ax 
    mov ah, 0x01 ; BIOS call to wait for key
    int 0x16
    jnz debug_mode
    %ENDIF 
    ; entering system check: 
    mov si,  enter_system_check
    
    mov si, sys_check_ok ; Put address of the null-terminated string to output into 'si'
    call print      ; Call our string-printing routine

    mov si, boot_system ; Put address of the null-terminated string to output into 'si'
    call print      ; Call our string-printing routine
    
    ;This goes first as to now overwrite %ah and %al.
    mov ax, 0x0050 
    mov es, ax                  ;Section to write into
    mov ah, 0x2                 ;Read sectors from drive
    mov al, 0x08                ;Number of sectors to read (31 * 512 = 15872 bytes)
    mov ch, 0x0                 ;Low 8 bits of cylinder
    mov cl, 0x11                ;First sector to read (bits 0-5), upper bits of cylinder (bits 6-7)
    mov dh, 0x0                 ;Head number
    mov dl, [disk_identifier]   ;Drive number
    mov bx, 0x0000               ;Offset into section
    int 0x13                    ;Low level disk services

    jnc notcarry
    mov si, error_str
    call print
    jmp endcarrycheck

    notcarry:
    mov si, success_str
    call print
    call printCRLF
    ;call printCRLF
    ;mov ax, cs
    ;call dumpax
    ;mov ax, start
    ;call dumpax
    ;call printCRLF
    
    mov dl, [disk_identifier]
    xor ax, ax
    mov al, dl
    call dumpax
    call printCRLF

    mov ax, 0x50
    mov ds, ax
    mov ax, 89 ; lba adress
    
    jmp 0x50:0x0000   ; Jump to the kernel 

endcarrycheck:  
    cli             ; Clear the Interrupt Flag (disable external interrupts)
    hlt             ; Halt the CPU (until the next external interrupt)

debug_mode: 
    mov si, .welcome_debug
    call print 
    cli             ; Clear the Interrupt Flag (disable external interrupts)
    hlt 

    .welcome_debug db 'This is debug mode', 0

;Routine for printing a 'ax' as hex
dumpax:
	pusha			; save registers
	mov bx, ax
	mov ah, 0xE		; Teletype output

	mov cx, 4		; 4 nipples in a 16 bit word
	.loop:
	rol bx, 4   	; rotate to next nipple
	mov al, bl		; we copy to al because we need to mask only the low 4 bits
	and al, 1111b	; Do the masking
	add al, '0'		; convert to ASCII
	cmp al, '9'		; If we are greater than 9 ascii, we add 7 to make digit 10 be represented as 'A'
	jbe .skip		;  -|-
	add al, 7		;  -|-
	.skip:			;  -|-
	int 0x10		; BIOS call 'output'
	loop .loop

	popa			; restore registers
	ret

printCRLF:
    mov ah, 0xE
    mov al, 13
    int 0x10
    mov al, 10
    int 0x10
    ret

; Routine for outputting string in 'si' register to screen
print:
    mov ah, 0xE     ; Specify 'int 0x10' 'teletype output' function
                    ; [AL = Character, BH = Page Number, BL = Colour (in graphics mode)]
.printchar:
    lodsb           ; Load byte at address SI into AL, and increment SI
    cmp al, 0
    je .done        ; If the character is zero (NUL), stop writing the string
    int 0x10         ; Otherwise, print the character via 'int 0x10'
    jmp .printchar  ; Repeat for the next character
.done:
    ret

data:
    message db 'Bootloader for SingOS! v0.1.0.10-exp',13,10,0
    enter_debug_mode db 'Press d to enter bootloader debug mode',13,10,0
    enter_system_check db 'Performing system check:',13,10,0
    sys_check_ok db 'System check ok', 13, 10, 0
    boot_system db 'Read SingOS from disk', 13, 10, 0
    error_str db 'Error', 0
    success_str db 'Success', 0
    disk_identifier db 0

; Pad to 510 bytes (boot sector size minus 2) with 0s, and finish with the two-byte standard boot signature
times 446-($-$$) db 0 ; First partion entry
db 0x80                 ; active partition
db 0, 0x00, 0x17        ; First sector CHS
db 0x18                 ; Disk type (Other) (Why 18, answer ':' ^ ')' )
db 0xff, 0xff, 0xff     ; Ending CHS values
db 0x18, 0, 0, 0x00        ; Staring LBA
db 0, 0xff, 0xff, 0xff  ; Size

db 0x00 
db 0x0, 0x0, 0x0 
db 0x0 
db 0x0, 0x0, 0x0 
db 0x00, 0x00, 0x00, 0x00 
db 0x0, 0x00, 0x00, 0x00

times 478-($-$$) db 0 ; Third partion entry

times 494-($-$$) db 0 ; Forth partion entry

times 510-($-$$) db 0
dw 0xAA55           ; => 0x55 0xAA (little endian byte order)
; bootloder debug_mode goes here

times 8192-($-$$) db 0

; From Version 0.0.3 we are concatinate the bootloader and the kernel after compile time
;%include "kernel.nasm"

;times 8192-($-$$) db 0 

;80 
;00 01 00 
;00 
;3F 60 21 
;00 00 00 00 
;00 10 09 00

;00 
;FE FF FF 
;EF 
;FE FF FF 
;B0 0E 00 00 
;40 03 00 00 

;00 
;00 00 00 
;00 
;00 00 00 
;00 00 00 00 
;00 00 00 00 

;00 
;00 
;00 00 00 00 
;00 00 00 00 
;00 00 00