fix some bugs in IEC ATN turnaround

c64/kernal/iec_turnaround_to_listen.s

@@ -2,6 +2,10 @@
 	;;  	pages 7--8.
 	
 iec_turnaround_to_listen:
+
+	jsr printf
+	.byte "DOING TURNAROUND",$0d,0
+	
 	;; Assert data and release clock
 	lda $dd00
 	sta $0420
@@ -12,8 +16,29 @@ iec_turnaround_to_listen:
 	;; Wait for clock line to be asserted by the drive
 *	lda $dd00
 	sta $0421
-	and #$80
+	and #$40
 	bne -
+
+	;;  Wait for clk to be released by the drive to mark ready to talk
+	ldx #$ff
+*	lda $dd00
+	and #$40
+	beq +
+	dex
+	bne -
+
+	jsr printf
+	.byte "TURNAROUND FAILED - FILE NOT FOUND?",$0d,$00
 	
+	;; Timeout = file not found error
+	;; (https://www.pagetable.com/?p=1023)
+	lda #5
+	sec
+	rts
+*
+	jsr printf
+	.byte "TURNAROUND SUCEEDED",$0d,$00
+
+	;; ATN turn around successful
+	cli
 	rts
-