%include "bootdef.inc"

[bits 16]

org BOOT_STAGE2_ADD


;k now read root directory
	mov	bx, BOOT_ROOT_SEG
	mov	ds, bx
	xor	si, si			;k now ds:si points to beginning of root directory
	mov	es, si
	mov	cx, 224			;max root entries
loop_compare:
	mov	di, kernel
	push	cx
	push	si			;save pointer to root dir entry
	mov	cx, 11
loop_name:
	cmpsb
	loopz	loop_name
	jnz	goon			;cx didn't get to zero, bad file
	pop	si
	pop	cx
	jmp	found_file		;good file, ds:si points to start of root directory entry
goon:
	pop	si
	pop	cx
	loop	loop_compare

error:
	jmp	$			;halt! no kernel file found!

found_file:				;ds:si points to root dir entry of kernel file
	mov	ax, [ds:si+26]
	mov	bx, BOOT_FAT_SEG
	mov	ds, bx			;ds points to beginning of FAT
	mov	edi, BOOT_KERNEL_ADD

readkernel_loop:
	cmp	ax, 0xff7
	jg	readkernel_done
	push	ax
	call	getCHSfromCluster
	mov	ax, 0x0201
	mov	dl, 0			;[brDrive]
	mov	bx, BOOT_KERNEL_SEG
	mov	es, bx
	xor	bx, bx
	int	0x13
	mov	cx, 256
	xor	ax, ax
	mov	es, ax
	mov	esi, BOOT_KERNEL_SEG*16
copykernel_loop:
	mov	ax, [es:esi]
	mov	[es:edi], ax
	inc	esi
	inc	esi
	inc	edi
	inc	edi
	loop	copykernel_loop

	pop	ax			;current logical cluster #

	mov	cx, ax			;cx=logical cluster
	mov	dx, 3
	mul	dx
	shr	ax, 1			;ax=logical cluster * 3 / 2
	mov	si, ax
	test	cl, 1			;is bit0 set?
	jnz	odd_cluster
even_cluster:
	lodsw
	and	ax, 0x0fff
	jmp	got_cluster
odd_cluster:
	lodsw
	shr	ax, 4
got_cluster:
	jmp	readkernel_loop

readkernel_done:

	jmp	go_pm

;------------------------------------------------------
getCHSfromCluster:
	;input: ax=lba of sector on floppy (0-2879)
	add	ax, 31			;convert logical cluster# to lba#
	xor	dx, dx			;lba->chs
	mov	bx, 18
	div	bx
	inc	dx
	mov	cl, dl			;sector# (1-18)
	xor	dx, dx
	mov	bx, 2
	div	bx
	mov	ch, al			;cylinder# (0-79)
	mov	dh, dl			;head# (0-1)
	ret


;-------------------------------------------------------
gdtr:
	dw	gdt_end-gdt-1
	dd	gdt
gdt:
	dd	0
	dd	0

KERNEL_CODE equ $-gdt
	db	0xff		;limit	7:0
	db	0xff		;limit	15:8
	db	0x00		;base	7:0
	db	0x00		;base	15:8
	db	0x00		;base	23:16
	db	0x9a		;access
	db	0xcf		;flags / limit 19:16
	db	0x00		;base	31:24

KERNEL_DATA equ $-gdt
	db	0xff		;segment 16 = 4gb data
	db	0xff
	db	0x00
	db	0x00
	db	0x00
	db	0x92
	db	0xcf		;cf
	db	0x00

gdt_end:

go_pm:
	xor	ax, ax
	mov	ds, ax
	lgdt	[gdtr]
	cli
	mov	eax, cr0
	inc	eax
	mov	cr0, eax

	jmp	KERNEL_CODE:pmode

bits 32
pmode:
	mov	ax, KERNEL_DATA
	mov	es, ax
	mov	ds, ax
	jmp	KERNEL_CODE:BOOT_KERNEL_ADD

kernel:	db	"KERNEL  BIN"
k_count: dw	0

times 510-($-$$)	db 0

db	0x55, 0xaa