vbr: read root directory into memory

boot/vbr.asm

@@ -16,8 +16,8 @@ fdc:		; FDC Descriptor as per ECMA-107
   db 0		; number of file allocation tables
 .rde:
   dw 0		; number of root directory entries
-.ts_old:
+.ts:
-  dw 0		; legacy: total number of sectors
+  dw 720	; total number of sectors
 .mi:		; medium identifier
   db 0xFD	; 5.25-inch Double sided, 40 tracks per side, 9 sectors per track (360 KB)
 .sf:		; sectors per fat
@@ -28,8 +28,8 @@ fdc:		; FDC Descriptor as per ECMA-107
   dw 2		; number of sides (heads)
 .po:
   dd 0		; partition offset (in LBA blocks)
-.ts:
+.lrgts:
-  dw 720
+  dw 0
 .drv:
   db 0		; drive number
   db 0
@@ -76,29 +76,60 @@ _startup:
   mul word [fdc.spt] ; number of sectors = number of tracks * sectors per track
   mov [fdc.ts], ax
 .noadjust:
-  mov ax, 0x0500
+  mov ax, 0x0070
   mov es, ax
-  mov bx, 0x0000
+  xor bx, bx
-  mov ax, 1
+  call loadrootdir
-  call loadblk
   call dump
-
-  mov al, [fdc.sc]
-  call print8
 .end:
   hlt
   jmp .end
 
-; Load a cluster from cluster offset
+; Load root directory into memory
-loadcluster:
+; in	es	data segment
+loadrootdir:
+  push bx
+  push cx
+  mov bx, [fdc.ss] ; bytes per sector
+  mov cl, 5
+  shr bx, cl ; div by 2^5, 32 bytes per directory entity
+  mov ax, [fdc.rde] ; number of root directory entities
+  xor dx, dx
+  div bx
+  mov cx, ax
+
+  mov ax, [fdc.sf]
+  mul byte [fdc.fn]
+  add ax, [fdc.rsc]
+
+  xor bx, bx ; load at beginning of es
+.loop:
+  call loadblk
+  loop .loop
+
+  pop cx
+  pop bx
   ret
 
-; Load a single cluster into memory
+; Load a cluster from cluster offset
+; in    ax      cluster number
+;       es:bx   buffer
+loadcl:
+  mov ax, [fdc.sf]
+  mul byte [fdc.fn]
+  add ax, [fdc.rsc]
+  call print16
+  ret
+
+; Load a single block into memory
 ; in    ax      sector number
 ;       es:bx	buffer
 ; out   al      error code,
 ;       carry set if error
 loadblk:
+  push ax
+  push cx
+  push dx
   xor dx, dx
   div word [fdc.spt]    ; ax:temp     = (lba / spt)
   inc dx                ; dx:sector   = (lba % spt) + 1
@@ -111,10 +142,15 @@ loadblk:
   mov dl, [fdc.drv] ; driver number
   mov ax, 0x0201 ; ah=0x02 al=0x01
   int 0x13
+  pop dx
+  pop cx
+  pop ax
+  inc ax
+  add bx, 0x0200
   ret
 
 dump:
-  mov si, 0x0000
+  mov si, bx
   mov cx, 0x10
 .nextline:
   mov ax, si