first hack at newfd function: compiles but doesn't work yet

git-svn-id: svn://svn.cc65.org/cc65/trunk@10 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/atari/fdtable.s

@@ -5,9 +5,13 @@
 ;
 
 	.include "atari.inc"
+	.importzp tmp2,ptr4,sp
+	.import	subysp,addysp
 	.export	fdtoiocb
 	.export	fdtoiocb_down
 	.export	fd_table
+	.export	fddecusage
+	.export	newfd
 
 	.data
 
@@ -31,6 +35,7 @@ ft_usa  = 0	; usage counter
 ft_iocb	= 1	; iocb index (0,$10,$20,etc.), $ff for empty entry
 ft_dev  = 2	; device of open iocb
 ft_flag = 3	; flags
+		; lower 3 bits: device number (for R: and D:)
 
 	.code
 
@@ -101,3 +106,124 @@ inval:	ldx	#$ff			; sets N
 	rts
 
 .endproc
+
+; decrements usage counter for fd
+; if 0 reached, it's marked as unused
+; get fd index in tmp2
+; Y register preserved
+.proc	fddecusage
+
+	lda	tmp2			; get fd
+	cmp	#MAX_FD_VAL
+	bcs	ret			; invalid index, do nothing
+	asl	a			; create index into fd table
+	asl	a
+	tax
+	lda	#$ff
+	cmp	fd_table+ft_iocb,x	; entry in use?
+	beq	ret			; no, do nothing
+	lda	fd_table+ft_usa,x	; get usage counter
+	beq	ret			; 0? should not happen
+	sec
+	sbc	#1			; decrement by one
+	sta	fd_table+ft_usa,x
+	bne	ret			; not 0
+	lda	#$ff			; 0, table entry unused now
+	sta	fd_table+ft_iocb,y	; clear table entry
+ret:	rts
+
+.endproc
+
+; newfd
+;
+; called from open() function
+; finds a fd to use for an open request
+; checks whether it's a device or file (file: characters following the ':')
+; files always get an exclusive slot
+; for devices it is checked whether the device is already open, and if yes,
+; a link to this open device is returned
+;
+; Calling paramteter:
+;	AX   - points to filename
+;	Y    - iocb to use (if we need a new open)
+; Return parameters:
+;	tmp2 - fd num
+;	C    - 0/1 for no open needed/open should be performed
+; all registers preserved!
+
+; local variables:
+;   AX     - 0 (A-0,X-1)
+;   Y      - 2
+;   ptr4   - 3,4  (backup)
+;   devnum - 5
+
+loc_A      = 0
+loc_X      = 1
+loc_Y      = 2
+loc_ptr4_l = 3
+loc_ptr4_h = 4
+loc_devnum = 5
+loc_size   = 6
+
+.proc	newfd
+
+	pha
+	txa
+	pha
+	tya
+	pha
+
+	ldy	#loc_size
+	jsr	subysp
+	ldy	#loc_devnum
+	lda	#0
+	sta	(sp),y		; loc_devnum
+	dey
+	lda	ptr4+1
+	sta	(sp),y		; loc_ptr4_h
+	dey
+	lda	ptr4
+	sta	(sp),y		; loc_ptr4_l
+	dey
+	pla
+	sta	(sp),y		; loc_Y
+	dey
+	pla
+	sta	(sp),y		; loc_X
+	sta	ptr4+1
+	dey
+	pla
+	sta	(sp),y		; loc_A
+	sta	ptr4
+
+	; ptr4 points to filename
+
+	ldy	#1
+	lda	#':'
+	cmp	(ptr4),y	; "X:"
+	beq	colon1
+	iny
+	cmp	(ptr4),y	; "Xn:"
+	beq	colon2
+
+	; no colon there!? OK, then we use a fresh iocb....
+
+do_open:nop			; @@@TODO
+	ldy	#loc_size
+	jsr	addysp
+	rts
+
+colon2:	dey
+	tya
+	pha
+	lda	(ptr4),y	; get device number
+	sec
+	sbc	#'0'
+	ldy	#loc_devnum
+	sta	(sp),y		; save it
+	pla
+	tay
+colon1:
+
+.endproc
+