From 5b704045633baa5be2842031dd35c8861c246cd6 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Wed, 24 Jul 2019 18:02:38 +0200
Subject: [PATCH] IEC turnaround move to proper (I hope...) places

---
 c64/kernal/chkinout.s                     |  3 ---
 c64/kernal/iec/iec_turnaround_to_listen.s | 15 ++++++++++-----
 c64/kernal/iec/iec_turnaround_to_talk.s   | 10 ++++++++--
 c64/kernal/iec/iec_tx_command.s           |  8 +-------
 c64/kernal/iec/iec_tx_command_finalize.s  | 20 ++++++++++++++++++++
 c64/kernal/load.s                         |  9 +++------
 c64/kernal/second.s                       | 12 ++++++++++--
 c64/kernal/talk.s                         |  2 --
 c64/kernal/tksa.s                         | 19 +++++++++++++++----
 c64/kernal/unlsn.s                        |  8 +++++---
 c64/kernal/untlk.s                        |  9 +++++----
 11 files changed, 77 insertions(+), 38 deletions(-)
 create mode 100644 c64/kernal/iec/iec_tx_command_finalize.s

diff --git a/c64/kernal/chkinout.s b/c64/kernal/chkinout.s
index d384b975..9a267264 100644
--- a/c64/kernal/chkinout.s
+++ b/c64/kernal/chkinout.s
@@ -52,9 +52,6 @@ chkin:
 	jsr tksa
 	bcs chkinout_end
 
-	jsr iec_turnaround_to_listen ;; XXX shouldn't this be sent by TALK/TKSA???
-	bcs chkinout_end
-
 chkin_set_device:
 	lda FAT,Y
 	sta DFLTN
diff --git a/c64/kernal/iec/iec_turnaround_to_listen.s b/c64/kernal/iec/iec_turnaround_to_listen.s
index 1033b720..0e66047a 100644
--- a/c64/kernal/iec/iec_turnaround_to_listen.s
+++ b/c64/kernal/iec/iec_turnaround_to_listen.s
@@ -4,6 +4,12 @@
 
 iec_turnaround_to_listen:
 
+	;; Store .X and .Y on the stack - preserve them
+	txa
+	pha
+	tya
+	pha
+
 	;; Timing is critical here - execute on disabled IRQs
 	php
 	sei
@@ -20,14 +26,13 @@ iec_turnaround_to_listen:
 	dex
 	bne -
 
-	;; Timeout
+	;; Timeout - XXX what errors do original Kernal report?
 	plp
-	sec
-	rts
+	jmp iec_return_DEVICE_NOT_FOUND
 
 	;; CLK is pulled by the device, OK
 *
 	plp
-	clc
-	rts
+	jmp iec_return_success
+
 
diff --git a/c64/kernal/iec/iec_turnaround_to_talk.s b/c64/kernal/iec/iec_turnaround_to_talk.s
index c24639d2..666c89e2 100644
--- a/c64/kernal/iec/iec_turnaround_to_talk.s
+++ b/c64/kernal/iec/iec_turnaround_to_talk.s
@@ -4,6 +4,12 @@
 
 iec_turnaround_to_talk:
 
+	;; Store .X and .Y on the stack - preserve them
+	txa
+	pha
+	tya
+	pha
+
 	;; Timing is critical here - execute on disabled IRQs
 	php
 	sei
@@ -19,5 +25,5 @@ iec_turnaround_to_talk:
 	jsr iec_pull_clk_release_data
 
 	plp
-	clc
-	rts
+	jmp iec_return_success
+
diff --git a/c64/kernal/iec/iec_tx_command.s b/c64/kernal/iec/iec_tx_command.s
index 153d0f6e..0e27f6af 100644
--- a/c64/kernal/iec/iec_tx_command.s
+++ b/c64/kernal/iec/iec_tx_command.s
@@ -55,12 +55,6 @@ iec_tx_command:
 
 	jmp iec_return_DEVICE_NOT_FOUND
 *
-	;; All done
-	
-	;; XXX All the documentation says we should release ATN at this point, but when I do so
-	;; the turnaround mechanism does not work. Why???
-	;; jsr iec_wait20us
-	;; jsr iec_set_idle
+	;; Done
 
 	jmp iec_return_success
-
diff --git a/c64/kernal/iec/iec_tx_command_finalize.s b/c64/kernal/iec/iec_tx_command_finalize.s
new file mode 100644
index 00000000..91ef8446
--- /dev/null
+++ b/c64/kernal/iec/iec_tx_command_finalize.s
@@ -0,0 +1,20 @@
+
+;; Routine to finalize these IEC commands which do not end in turnaround
+;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
+
+
+iec_tx_command_finalize:
+
+	;; Store .X and .Y on the stack - preserve them
+	txa
+	pha
+	tya
+	pha
+
+	;; Give device some time to complete command reception, release ATN,
+	;; give it some time again before (possible) next command
+	jsr iec_wait20us
+	jsr iec_set_idle
+	jsr iec_wait20us
+
+	jmp iec_return_success
diff --git a/c64/kernal/load.s b/c64/kernal/load.s
index 9675f2df..e83d3a6b 100644
--- a/c64/kernal/load.s
+++ b/c64/kernal/load.s
@@ -63,8 +63,9 @@ load:
 	bcs lvs_device_not_found_error
 
 	;; Open channel #0 (p16)
-	lda #$00
-	jsr tksa
+	lda #$F0 ; $F0 for TKSA + 0 for channel number
+	sta BSOUR
+	jsr iec_tx_command
 	bcs lvs_load_verify_error
 
 	;; Send filename (p16)
@@ -155,10 +156,6 @@ load_loop:
 	;; Command drive to stop talking and to close the file
 	jsr untlk
 
-	;; Turnaround to talker - according to https://www.pagetable.com/?p=1135
-	;; the turnaround only happens after a command
-	jsr iec_turnaround_to_talk
-
 	lda current_device_number
 	jsr listen
 
diff --git a/c64/kernal/second.s b/c64/kernal/second.s
index 53d1391e..819fdc24 100644
--- a/c64/kernal/second.s
+++ b/c64/kernal/second.s
@@ -12,7 +12,15 @@
 
 second:
 
-	and #$1F ; make sure bits encoding the command are cleared out
+	;; Due to TKSA/SECOND command encoding (see https://www.pagetable.com/?p=1031),
+	;; allowed channels are 0-15; report error if out of range
+	cmp #$10
+	bcs kernalerror_FILE_NOT_INPUT
+
 	ora #$60
 	sta BSOUR
-	jmp iec_tx_command
+	jsr iec_tx_command
+	bcs + ; branch if error
+	jmp iec_tx_command_finalize
+*
+	rts
diff --git a/c64/kernal/talk.s b/c64/kernal/talk.s
index 3952ed0c..46c26c35 100644
--- a/c64/kernal/talk.s
+++ b/c64/kernal/talk.s
@@ -10,8 +10,6 @@
 ;;
 
 
-;; XXX shouldn't this do a turnaround?
-
 talk:
 
 	;; First check whether device number is correct
diff --git a/c64/kernal/tksa.s b/c64/kernal/tksa.s
index d003cfbb..06953f7d 100644
--- a/c64/kernal/tksa.s
+++ b/c64/kernal/tksa.s
@@ -10,12 +10,23 @@
 ;;
 
 
-;; XXX shouldn't this do a turnaround?
-
 tksa:
 
-	and #$1F ; make sure bits encoding the command are cleared out
+	;; Due to TKSA/SECOND command encoding (see https://www.pagetable.com/?p=1031),
+	;; allowed channels are 0-15; report error if out of range
+	cmp #$10
+	bcs kernalerror_FILE_NOT_INPUT
+
 	ora #$F0
 	sta BSOUR
-	jmp iec_tx_command
+	jsr iec_tx_command
+	bcs + ; branch if error
+	;; XXX - is it really the right place to do a turnaround? I've got some doubts
+	;; (it forces us to send the TKSA command 'manually' sometimes), but
+	;; Luigi Di Fraia (https://luigidifraia.wordpress.com/2017/06/27/codebase64-on-the-kernal-behaviour/)
+	;; claims TKSA Kernal routine actually does the turnaround
+	jmp iec_turnaround_to_listen
+*
+	rts
+
 
diff --git a/c64/kernal/unlsn.s b/c64/kernal/unlsn.s
index 32f0b0f5..5aa2cfdc 100644
--- a/c64/kernal/unlsn.s
+++ b/c64/kernal/unlsn.s
@@ -23,6 +23,8 @@ unlsn:
 	;; Buffer empty, send the command
 	lda #$3F
 	sta BSOUR
-	jmp iec_tx_command
-
-
+	jsr iec_tx_command
+	bcs + ; branch if error
+	jmp iec_tx_command_finalize
+*
+	rts
diff --git a/c64/kernal/untlk.s b/c64/kernal/untlk.s
index 7f421bb7..4ec846a8 100644
--- a/c64/kernal/untlk.s
+++ b/c64/kernal/untlk.s
@@ -10,11 +10,12 @@
 ;;
 
 
-;; XXX shouldn't this do a turnaround?
-
 untlk:
 
 	lda #$5F
 	sta BSOUR
-	jmp iec_tx_command
-
+	jsr iec_tx_command
+	bcs + ; branch if error
+	jmp iec_turnaround_to_listen
+*
+	rts