Make logging in drive a no-op if drive already logged in

boot/kernel.asm

@@ -29,10 +29,7 @@ print_banner:	mov si, banner
 		sub dl, (0x80-2)
 .k:		mov [defdrv], dl
 
-		call dskrst
-
-		mov dl, [defdrv]
-		call logdrv
+		call logdrv.force
 
 		xor ax, ax
 		xor dx, dx

kernel/drive.asm

@@ -28,38 +28,38 @@ bpb:		resb BPBSIZ4
 
 section .text
 
-dskrst:		call flush
-		mov ax, 0xFFFF
-		mov [dsknum], al
-		mov [dskseek], ax
-		mov [dskseek+2], ax
-		ret
-
 		; log in drive
 		; currently only supports 18 sectors 2 heads floppies
 		; IN	dl	drive number
-logdrv:		push dx
-		call dskrst
+logdrv:		; dont do anything if drive already selected
+		cmp dl, [dsknum]
+		je .ret
+		; clear out current contents
+.force:		push dx
+		call flush
+		mov ax, 0xFFFF
+		mov [dskseek], ax
+		mov [dskseek+2], ax
+		mov byte [dskflag], 0
 		pop dx
-
+		; set current drive number
+		mov [dsknum], dl
+		; save info for bios
 		mov [biosnum], dl
-
+		; load boot sector
 		xor ax, ax
 		xor dx, dx
 		call mapabs
-
 		; copy bios parameter block
 		lea si, [dskbuf+BPBOFF]
 		mov di, bpb
 		mov cx, BPBSIZ4
 		rep movsb
-
 		; make sure partition offset is forced zero
 		xor ax, ax
 		mov [bpb+BPBHS], ax
 		mov [bpb+BPBHS+2], ax
-
-		ret
+.ret:		ret
 
 calchs:		mov bx, (18*2)
 		; dx:ax = linear count, bx = sectors / cylinder