format binary
use32
org 0x100000

MB_HEADER_MAGIC      equ 0x1BADB002
MB_PAGE_ALIGN        equ (1 shl 0)
MB_MEMORY_INFO       equ (1 shl 1)
MB_VIDEO_REQUEST     equ (1 shl 2)
MB_AOUT_KLUDGE       equ (1 shl 16)
MB_HEADER_FLAGS      equ MB_PAGE_ALIGN or MB_MEMORY_INFO or MB_VIDEO_REQUEST
MB_HEADER_FLAGS      equ MB_PAGE_ALIGN or MB_MEMORY_INFO or MB_VIDEO_REQUEST or MB_AOUT_KLUDGE
MB_CHECKSUM          equ -(MB_HEADER_MAGIC + MB_HEADER_FLAGS)

;; safe modes according to https://wiki.osdev.org/VESA_Video_Modes
VWIDTH  equ 80 ; 640/720
VHEIGHT equ 25 ; 480
VDEPTH  equ 0  ; 24/32, zero in textmode

multiboot:
	dd MB_HEADER_MAGIC
	dd MB_HEADER_FLAGS
	dd MB_CHECKSUM
	dd multiboot	; header address
	dd 0x100000	; load address
	dd bss_start	; load end address
	dd bss_end	; bss end address
	dd start	; entry address

	dd 1	; video mode_type (0:fb, 1:txt) (set flags[2]!)
	dd VWIDTH	; video width
	dd VHEIGHT	; video height
	dd VDEPTH	; video depth

start:
	; Setup stack
	mov ebp, stack_top
	mov esp, stack_top

	;push ebx ; mboot info struct addr
	;push eax ; 0x2BADB002

	mov [mbootmagic], eax
	;mov [mbootaddr], ebx

	call con_disable_cursor
	call conclear

	mov esi, msg.roskainiting
	call conwriteln


hang:
	;cli
	.loop:
		;hlt
		jmp .loop

;give character in AL
conputchar:
	mov ah, [txtbuf.col]
	mov dx, ax
	; dx has the whole character cell now
	xor eax, eax
	mov al, [txtbuf.y]
	mov bl, 80
	mul bl
	movzx bx, [txtbuf.x]
	add ax, bx
	add ax, ax
	add eax, 0xb8000
	mov [eax], dx
	cmp bl, 79
	je connewline
	inc bl
	mov [txtbuf.x], bl
	ret
conwriteln:
	lodsb
	cmp al, 0
	je connewline
	call conputchar
	jmp conwriteln
connewline:
	mov [txtbuf.x], 0
	mov al, [txtbuf.y]
	cmp al, 24
	je conscroll
	inc al
	mov [txtbuf.y], al
	ret
conscroll:
	ret

conclear:
	mov ecx, 80*25
	mov edi, 0xb8000
	mov ah, 0x07
	mov al, 0
	rep stosw
	mov [txtbuf.col], ah
	mov [txtbuf.x], 0
	mov [txtbuf.y], 0
	ret

con_disable_cursor:
	mov dx, 0x3D4
	mov al, 0xA	; low cursor shape register
	out dx, al

	inc dx
	mov al, 0x20	; bits 6-7 unused, bit 5 disables the cursor, bits 0-4 control the cursor shape
	out dx, al
	ret

mbootaddr: dd 0
mbootmagic: dd 0
txtbuf:
	.x db 0
	.y db 0
	.col db 0x07 ;gray on black

fb:
	.addr dd 0
	.pitch dd 0
	.width dd 0
	.height dd 0
	.depth db 0
	.bytespp db 0
	.rpos db 0
	;.rmasksize db 0
	.gpos db 0
	;.gmasksize db 0
	.bpos db 0
	;.bmasksize db 0

msg:
	.roskainiting db "rOSka initializing...", 0

align 4096
bss_start:
align 4096
stack_bottom:
rb 16384
stack_top:
bss_end: