From 7455b795859e0251e79bc20a3915061cdaa1d32e Mon Sep 17 00:00:00 2001
From: d0p1 <contact@d0p1.eu>
Date: Wed, 27 May 2020 18:36:29 +0200
Subject: [PATCH] wip: load kernel from FAT

---
 Makefile      |  12 +++--
 boot/floppy.s | 130 ++++++++++++++++++++++++++++++++++----------------
 kern/kernel.s |   1 +
 3 files changed, 96 insertions(+), 47 deletions(-)

diff --git a/Makefile b/Makefile
index 261883c..37fe02e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,9 @@
-all: stupid.img
+all: stupid.img kern.bin
 
 stupid.img: floppy.bin kern.bin
-	cat $^ /dev/zero | dd of=$@ bs=512 count=2880
+	mkdosfs -F 12 -C $@ 1440
+	dd status=noxfer conv=notrunc if=floppy.bin of=$@
+	mcopy -i $@ kern.bin ::kern.sys
 
 floppy.bin: boot/floppy.s
 	nasm -fbin -o $@ $^
@@ -10,10 +12,10 @@ kern.bin: kern/kernel.s
 	nasm -fbin -o $@ $^
 
 clean:
-	rm floppy.bin kern.bin
+	rm -rf floppy.bin kern.bin
 
-fclean:
-	rm stupid.img
+fclean: clean
+	rm -rf stupid.img
 
 re: fclean all
 
diff --git a/boot/floppy.s b/boot/floppy.s
index 69d9108..52f5c49 100644
--- a/boot/floppy.s
+++ b/boot/floppy.s
@@ -9,25 +9,65 @@
 	;; -----------------------------------------------------------
 	db "StupidOS"
 
-	dw 512 			; bytes per sector
-	db 1			; sector per cluster
-	dw 1			; reserved sector
-	db 2			; number of FATs
-	dw 224			; root entries
-	dw 2400			; total sector
-	db 0xF9			; media descriptor type
-	dw 7			; sectors per FAT
-	dw 15			; sectors per track
-	dw 2			; heads per cylinder
-	dd 0			; hidden sectors
-	dd 0			; total sector big
-	db 0			; drive number
-	db 0			; unused
-	db 0x29 		; drive signature (0x29 = floppy) 
-	dd 0x00000000		; serial number (ignore)
-	db 'STUPID DISK'	; volume label
-	db 'FAT12   '		; filesystem type
+bpb_bytes_per_sector	dw 512 			; bytes per sector
+bpb_sectors_per_cluster	db 1			; sector per cluster
+bpb_reserved_sectors	dw 1			; reserved sector
+bpb_number_of_fats	db 2			; number of FATs
+bpb_root_entries	dw 224			; root entries
+bpb_total_sectors	dw 2880			; total sector
+bpb_media		db 0xF0			; media descriptor type
+bpb_sectors_per_fat	dw 9			; sectors per FAT
+bpb_sectors_per_track	dw 18			; sectors per track
+bpb_heads_per_cylinder	dw 2			; heads per cylinder
+bpb_hidden_sectors	dd 0			; hidden sectors
+bpb_total_sector_big	dd 0			; total sector big
+bpb_drive_number	db 0			; drive number
+bpb_unused		db 0			; unused
+bpb_signature		db 0x29 		; drive signature (0x29 = floppy) 
+bpb_serial_number	dd 0x00000000		; serial number (ignore)
+bpb_volume_label	db 'STUPID DISK'	; volume label
+bpb_filesystem		db 'FAT12   '		; filesystem type
+
+	;; -----------------------------------------------------------
+	;; entry
+	;; -----------------------------------------------------------
+entry:
+	xor ax, ax
+	mov ds, ax
+
+	mov si, msg_boot
+	call boot_print
+	mov si, msg_copyright
+	call boot_print
+reset_disk:
+	xor ah, ah
+	xor dl, dl
+	int 0x13
+	jc reset_disk
+
+	;; load kernel from FAT
+	;; store size of root dir in cx
+	xor cx, cx
+	xor dx, dx
+	mov ax, 0x0020
+	mul word [bpb_root_entries]
+	div word [bpb_bytes_per_sector]
+	xchg ax, cx
+
+	;; store loc of root directory in ax
+	mov al, byte [bpb_number_of_fats]
+	mul word [bpb_sectors_per_fat]
+	add ax, word [bpb_reserved_sectors]
+	;; mov word [datasec], ax
+	;; mov word [datasec], cx
 	
+	mov bx, 0x0200
+	
+hang:
+	jmp hang
+	cli
+	hlt
+
 	;; -----------------------------------------------------------
 	;; Print string using bios interrupt
 	;; -----------------------------------------------------------
@@ -45,36 +85,42 @@ boot_print:
 	popa
 	ret
 
+fatal_error:
+	pusha
+	mov cx, si
+	mov si, msg_error
+	call boot_print
+	mov si, cx
+	call boot_print
+	mov si, msg_press_any_key
+	call boot_print
+	xor ax, ax
+	int 0x16		; wait keypressed 
+	int 0x19		; reboot
+	popa
+	ret
+
+disk_read_sector:
+	pusha
+	
+	popa
+	ret
+	
 	;; -----------------------------------------------------------
 	;; Variables
 	;; -----------------------------------------------------------
-	copyright db "Copyright (c) d0p1", 13, 10, 0
-	err_disk_reset db "Error reseting disk..retry", 13, 10, 0
+	msg_boot db "StupidOS - Bootloader", 13, 10, 0
+	msg_copyright db "Copyright (c) d0p1", 13, 10, 0
+	msg_press_any_key db "Press any key...", 13, 10, 0
+
+	msg_error db "[ERROR] ", 0
+	err_kern_not_found db "KERNEL.BIN not found...", 13, 10, 0
+
+	kernel_filename db "KERNEL  BIN"
 
 	;; -----------------------------------------------------------
-	;; entry
+	;; End
 	;; -----------------------------------------------------------
-entry:
-	xor ax, ax
-	mov ds, ax
-
-	mov si, copyright
-	call boot_print
-reset_disk:
-	xor ah, ah
-	xor dl, dl
-	int 0x13
-	jnc .reset_disk_end
-	mov si, err_disk_reset
-	call boot_print
-	jmp reset_disk
-.reset_disk_end:
-	
-hang:
-	jmp hang
-	cli
-	hlt
-
 	times 510-($-$$) db 0
 	db 0x55
 	db 0xAA
diff --git a/kern/kernel.s b/kern/kernel.s
index e69de29..8a93847 100644
--- a/kern/kernel.s
+++ b/kern/kernel.s
@@ -0,0 +1 @@
+[BITS 16]