From ae90faf4d6f47a8fe8b94b2c2516cdd28f36debc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Mon, 28 Jun 2021 22:58:11 +0300
Subject: [PATCH] List root directory of the disk

---
 Makefile       |  10 +++-
 bootsector.asm | 123 +++++++++++++++++++++++++++++++++++++++++++++++--
 hexprint.inc   |  32 +++++++++++++
 kernel.asm     |   0
 4 files changed, 160 insertions(+), 5 deletions(-)
 create mode 100644 hexprint.inc
 create mode 100644 kernel.asm

diff --git a/Makefile b/Makefile
index cd02a38..b7c94c3 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,13 @@
 .SUFFIXES:
 .SUFFIXES: .bin .asm
 
-all: bootsector.bin
+all: nor86.img
+
+nor86.img: bootsector.bin kernel.bin
+	rm -f $@
+	mkdosfs -C $@ 1440
+	rw -i bootsector.bin -o $@
+	mcopy -i $@ kernel.bin ::
 
 .asm.bin:
 	nasm -fbin -o $@ $<
@@ -9,7 +15,7 @@ all: bootsector.bin
 clean:
 	rm -f *.bin *.img
 
-run: bootsector.bin
+run: nor86.img
 	qemu-system-i386 -fda $<
 
 .PHONY: all clean run
diff --git a/bootsector.asm b/bootsector.asm
index 5a7e102..040fa1e 100644
--- a/bootsector.asm
+++ b/bootsector.asm
@@ -21,7 +21,7 @@ hiddensectors     dd 0
 totalsectorslarge dd 0
 
 ; EBPB
-drivenumber       db 0 ; useless
+drivenumber       db 0 ; useless on-disk, used as a variable
 reserved          db 0 ; winnt flags
 signature         db 0x29 ; mkdosfs uses this, dunno how 0x28 differs
 serial            dd 0
@@ -32,12 +32,129 @@ _code:
 	jmp 0:_start
 
 _start:
-	mov ax, 0x0e40
-	int 0x10
+	cld
+	; Set up segments
+	mov ax, cs
+	mov ds, ax
+	mov es, ax
+	cli
+	mov ss, ax
+	mov sp, 0x7c00
+	sti
+
+	; Save bootdrive
+	mov [drivenumber], dl
+
+root_dir:
+	; Disk organization:
+	; Reserved sectors (MBR)
+	; FAT1
+	; FAT2
+	; Root dir
+	; → Root dir starts at LBA reservedsectors + fats*sectorsperfat
+	xor ah, ah
+	mov al, [fats]
+	mul word [sectorsperfat]
+	add ax, [reservedsectors]
+	mov [rootdir], ax
+
+	call chs
+
+	mov ah, 2
+	mov al, 14 ; TODO: don't hardcode
+	mov dl, [drivenumber]
+	mov bx, 0x500
+	int 0x13
+
+print_root:
+	mov byte [0x500 + 32*224], 0 ; TODO: don't hardcode
+	mov si, 0x500
+	.entry:
+		cmp byte [si], 0
+		je .end
+
+		test byte [si + 11], 0x08 + 0x10
+		jz .isfile
+
+		add si, 32
+		jmp .entry
+
+	.isfile:
+		mov ah, 0xe
+		mov cx, 8
+		.name:
+			lodsb
+			int 0x10
+			loop .name
+
+		mov al, ' '
+		int 0x10
+
+		mov cx, 3
+		.ext:
+			lodsb
+			int 0x10
+			loop .ext
+
+		mov al, 13
+		int 0x10
+		mov al, 10
+		int 0x10
+
+		add si, 32 - 11
+		jmp .entry
+
+	.end:
 
 hang:
 	hlt
 	jmp hang
 
+chs:
+	push ax
+	push bx
+
+	; Save drive number
+	mov bl, dl
+
+	xor dx, dx
+	; cylinder (track) - head - sector
+	; cylinder = LBA / sectorspertrack / heads
+	; head = LBA / sectorspertrack % heads
+	; sector = LBA % sectorspertrack + 1
+	div word [sectorspertrack]
+	; ax = LBA / sectorspertrack
+	; dx = LBA % sectorspertrack
+
+	; sector
+	mov cl, dl
+	inc cl
+
+	xor dx, dx
+	div word [heads]
+	; ax = LBA / sectorspertrack / heads
+	; dx = LBA / sectorspertrack % heads
+
+	; head
+	mov dh, dl
+
+	; cylinder (track)
+	mov ch, al
+	;shr ax, 1
+	;shr ax, 1
+	;and al, 0xC0
+	;or cl, al
+
+	; Restore drive number
+	mov dl, bl
+
+	pop bx
+	pop ax
+	ret
+
+%include "hexprint.inc"
+
 times 510-($-$$) db 0
 db 0x55, 0xaa
+_end:
+rootdir equ _end
diff --git a/hexprint.inc b/hexprint.inc
new file mode 100644
index 0000000..1315fcd
--- /dev/null
+++ b/hexprint.inc
@@ -0,0 +1,32 @@
+hexprint16:
+	xchg ah, al
+	call hexprint8
+	xchg ah, al
+
+hexprint8:
+	push ax
+	push bx
+	push cx
+	mov cl, al
+	xor bx, bx
+
+	mov ah, 0xe
+	shr al, 1
+	shr al, 1
+	shr al, 1
+	shr al, 1
+	mov bl, al
+	mov al, [.digits + bx]
+	int 0x10
+
+	mov bl, 0xf
+	and bl, cl
+	mov al, [.digits + bx]
+	int 0x10
+
+	pop cx
+	pop bx
+	pop ax
+	ret
+
+	.digits: db '0123456789abcdef'
diff --git a/kernel.asm b/kernel.asm
new file mode 100644
index 0000000..e69de29