added turnaround to talker to IEC support

c64/kernal/iec_turnaround_to_talk.s

@@ -4,9 +4,15 @@
 
 iec_turnaround_to_talk:
 
-	;; XXX implement this
+	;; First make sure both CLK, DATA and ATN are released at our side
+	jsr iec_release_atn
+	jsr iec_release_clk_data
+
+	;; Wait till device releases CLK line
+	jsr iec_wait_for_clk_release
+
+	;; Pull CLK line, it should be held by talker
+	jsr iec_pull_clk_release_data
 
 	clc
 	rts
-
-

c64/kernal/iec_wait_for_data_pull.s

@@ -0,0 +1,7 @@
+
+iec_wait_for_data_pull:
+	lda CI2PRA
+	;; Check the highest bit, which is DATA IN,
+	;; (highest bit set = negative value)
+	bmi iec_wait_for_data_pull
+	rts

c64/kernal/load.s

@@ -198,16 +198,14 @@ load_done:
 	lda #$0D
 	jsr JCHROUT
 *
-	;; Close file on drive - start by turnaround to talker
+	;; Close file on drive
-	jsr iec_turnaround_to_talk
 
 	;; Command drive to stop talking and to close the file
 	jsr untlk
 
-	;; XXX XXX code below runs into infinite loop - so for now just quit
+	;; Turnaround to talker - according to https://www.pagetable.com/?p=1135
-	clc
+	;; the turnaround only happens after a command
-	cli
+	jsr iec_turnaround_to_talk
-	rts
 
 	lda current_device_number
 	jsr listen