Implement current drive for user programs

kernel/fcb.asm

@@ -1,22 +1,20 @@
-section .bss
-
-		; default drive if field in FCB = 0
-defdrv:		resb 1
-
 section .text
 
-		; Helper function: read the drive number from FCB,
-		; apply default if necessary,
-		; and make it current I/O drive
-_setdrv:	mov dl, [es:bx] ; A=1
-		test dl, dl
-		jnz .nofix
-		mov dl, [defdrv] ; A=0
-		inc dl
-		mov [es:bx], dl ; A=1
-		; now set as current i/o drive
-.nofix:		dec dl ; A=0 for dsksel
-		jmp logdrv
+		; set default drive for current process
+		; IN	dl	drive number
+setdd:		push ds
+		mov ds, [ss:curpsp]
+		mov [PSPDD], dl
+		pop ds
+		ret
+
+		; get default drive for current process
+		; OUT	al	drive number
+getdd:		push ds
+		mov ds, [ss:curpsp]
+		mov al, [PSPDD]
+		pop ds
+		ret
 
 		; Load root directory entry
 		; IN	ax	number of directory entry

kernel/syscall.asm

@@ -31,8 +31,8 @@ stab:	; syscall table
 	dw err, sret ; console status
 	dw err, sret ; return version num
 	dw err, sret ; reset disks
-	dw err, sret ; select disk
-	dw err, sret ; open file
+	dw setdd, sret ; select disk
+	dw err, sretb ; open file
 .end:
 
 section .text
@@ -56,6 +56,9 @@ PSPDS:	resw 1
 PSPBX:	resw 1
 PSPES:	resw 1
 
+	; default drive
+PSPDD:	resb 1
+
 section .text
 
 	; Load current PSP segment into DS