# File              : entry.S
# Author            : Robin Krens <robin@robinkrens.nl>
# Date              : 07.06.2022
# Last Modified Date: 07.06.2022
# Last Modified By  : Robin Krens <robin@robinkrens.nl>

.org	0
.code16

.extern	main
.extern _stext
.extern _etext
.extern _sdata
.extern _edata
.extern scroll_video

.global _start
.global dummyS_isr

_start:
	# reset flags and registers
	cli
	cld
	xor %ax,%ax
	mov %ax,%bx
	mov %ax,%bp
	mov %ax,%ss
	
	# set correct segment (use at
	# position 0x2000 + 0 + IP
	mov $0x2000, %bx
	mov %bx, %cs
	xor %bx, %bx

	# set stack pointer for wonderswan
	# color
	mov $0xFE00 - 2,%ax
	mov %ax,%sp
	
copy_to_ram:
	mov $_etext, %ax
	# set data segment to ROM bank
	mov $0x2000, %bx
	mov %bx, %ds
	mov %ax, %si
	mov $_sdata, %bx
	mov %bx, %di
	# calculate size
	mov $_edata, %ax
	mov $_sdata, %bx
	sub %bx, %ax
	mov %ax, %cx
	rep movsb
	# reset data segment to RAM
	xor %ax, %ax
	mov %ax, %ds


	# jump to C
	call main

dummyS_isr:
	push %ax
	call scroll_video
	;xor %ax, %ax
	;in $0x12, %al
	;inc %al
	;out %al, $0x12
	pop %ax
	iret

	# should not be here
loop:	nop
	jmp loop