Begin work on filesystem support

Makefile

@@ -9,7 +9,7 @@ all: ponydos.img
 ponydos.img: ponydos.bin wallpaper.bin
 	rw -i /dev/zero -o $@ -c 1440K
 	rw -i ponydos.bin -o $@
-	rw -i wallpaper.bin -o $@ -O 512
+	rw -i wallpaper.bin -o $@ -O 1024
 
 .asm.bin:
 	$(NASM) -fbin -o $@ $<

filesystem.asm

@@ -0,0 +1,14 @@
+; TODO: have tooling for this
+
+; 128 sector files, starting at 2
+
+; dirent:
+;  2 bytes size in 512B sectors, 0 for end of listing
+;  30 bytes null-terminated name
+
+wallpaper:
+	dw 8
+	db 'wallpaper.bin', 0
+	times 512+32-($-$$) db 0
+
+times 1024-($-$$) db 0

ponydos.asm

@@ -8,12 +8,14 @@ ROWS equ 25
 
 WALLPAPER equ 0x500
 
+DIRENTS equ 0x2000
+DIRENT_SIZE equ 32
+FILE_MAX_SIZE equ 128
+
 jmp 0:start
 start:
 	cld
 
-	cli
-
 	; Set up segments and stack
 	mov ax, cs
 	mov ds, ax
@@ -21,12 +23,10 @@ start:
 	mov ss, ax
 	mov sp, $$
 
-	sti
-
 	; Clear BSS
+	;xor al, al
 	mov di, _bss_start
 	mov cx, _bss_end - _bss_start
-	xor al, al
 	rep stosb
 
 	mov [boot_disk], dl
@@ -65,11 +65,11 @@ initialize_mouse:
 	.done:
 
 load_wallpaper:
-	mov ax, 1
-	mov bl, [boot_disk]
-	mov cx, 8
-	mov di, WALLPAPER
+	mov si, wallpaper_name
+	call open_file
+	mov bx, WALLPAPER
 	call read_sectors
+	; TODO: error management? Surely this works...
 
 initialize_screen:
 	; Disable text cursor
@@ -164,35 +164,31 @@ flip_mouse_cursor:
 
 ; in:
 ;  ax = LBA of first sector
-;  bl = drive number
+;;  bl = drive number
 ;  cx = number of sectors to read (must be at least 1)
-;  es:di = output buffer
+;  es:bx = output buffer
 read_sectors:
 	push ax
 	push cx
-	push di
+	push bx
 
 	.loop:
 		call read_sector
 		inc ax
-		add di, 512
+		add bx, 512
 		loop .loop
 
-	pop di
+	pop bx
 	pop cx
 	pop ax
 	ret
 
 ; in:
-;  ax = LBA of first sector
-;  bl = drive number
-;  es:di = output buffer
-read_sector:
-	push ax
-	push bx
-	push cx
-	push dx
-
+;  ax = LBA of sector
+; out:
+;  cx, dx = appropriately set for int 0x13
+;  ax clobbered
+prepare_geometry:
 	mov cx, 18
 	div cx
 
@@ -209,10 +205,19 @@ read_sector:
 	mov ch, al
 
 	; dl = drive number
-	mov dl, bl
+	mov dl, [boot_disk]
+	ret
 
-	; es:bx = output buffer
-	mov bx, di
+; in:
+;  ax = LBA of first sector
+;;  bl = drive number, use [boot_disk] for now
+;  es:bx = output buffer
+read_sector:
+	push ax
+	push cx
+	push dx
+
+	call prepare_geometry
 
 	.retry:
 	mov ax, 0x0201 ; read one sector
@@ -221,7 +226,6 @@ read_sector:
 
 	pop dx
 	pop cx
-	pop bx
 	pop ax
 	ret
 
@@ -233,6 +237,112 @@ read_sector:
 		int 0x10
 		jmp .retry
 
+; in:
+;  ax = LBA of first sector
+;;  bl = drive number, use [boot_disk] for now
+;  es:bx = input buffer
+write_sector:
+	push ax
+	push cx
+	push dx
+
+	call prepare_geometry
+
+	.retry:
+	mov ax, 0x0301 ; write one sector
+	int 0x13
+	jc .error
+
+	pop dx
+	pop cx
+	pop ax
+	ret
+
+	.error:
+		xor ah, ah
+		int 0x10
+		jmp .retry
+
+; ------------------------------------------------------------------
+; Filesystem
+; ------------------------------------------------------------------
+
+wallpaper_name: db 'wallpaper.bin', 0
+
+; in:
+;  es:si = file name
+; out:
+;  ax = LBA of first sector, 0 if no space left
+;  cx = length in sectors
+open_file:
+	push si
+	push di
+	push bx
+
+	; Stolen from https://stackoverflow.com/a/72746473, get strlen in cx
+	mov di, si
+	mov cx, -1
+	xor ax, ax
+	repne scasb
+	not cx
+	dec cx
+
+	;mov ax, 1
+	mov al, 1
+	mov bx, DIRENTS
+	call read_sector
+
+	mov ax, 2
+	mov di, bx
+	.loop:
+		cmp word [di], 0
+		je .create_file
+
+		inc di
+		inc di
+
+		push cx
+		push di
+		push si
+		repe cmpsb
+		pop si
+		pop di
+		pop cx
+		je .success
+
+		add ax, FILE_MAX_SIZE
+		add di, DIRENT_SIZE - 2
+		cmp di, DIRENTS + 0x200
+		jl .loop
+
+	.error:
+	xor ax, ax
+	; Return with mangled cx
+	.success:
+	mov cx, [di - 2]
+	.return:
+	pop bx
+	pop di
+	pop si
+	ret
+
+	.create_file:
+		; TODO: zero out the sector for this file?
+		inc word [di]
+		inc di
+		inc di
+		rep movsb
+		
+		push ax
+		mov ax, 1
+		;mov bx, DIRENTS
+		call write_sector
+		pop ax
+		
+		;mov cx, 1
+		mov cl, 1
+		jmp .return
+
 ; ------------------------------------------------------------------
 ; Mouse callback
 ; ------------------------------------------------------------------
@@ -315,6 +425,7 @@ mouse_handler:
 ; Debug routines
 ; ------------------------------------------------------------------
 
+%if 0
 hexprint16:
 	xchg ah, al
 	call hexprint8
@@ -347,15 +458,19 @@ hexprint4:
 hang:
 	hlt
 	jmp hang
+%endif
 
 ; ------------------------------------------------------------------
 ; Padding and boot sector signature
 ; ------------------------------------------------------------------
 
 times 510-($-$$) db 0
+
 db 0x55
 db 0xaa
 
+%include "filesystem.asm"
+
 ; ------------------------------------------------------------------
 ; Zero-initialized variables
 ; ------------------------------------------------------------------
@@ -372,4 +487,4 @@ mouse_row resw 1
 
 boot_disk resb 1
 
-_bss_end:
+_bss_end: