From a1d3c74a0d1f201db005f8164f39deaf05a6be08 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Sat, 22 Jun 2019 15:52:09 +0200
Subject: [PATCH] more IEC work - the turnaround seems to work now

---
 ...lease_atn_clock.s => iec_pull_data_release_atn_clk.s} | 0
 c64/kernal/iec_release_atn.s                             | 8 ++++++++
 c64/kernal/iec_tx_command.s                              | 9 ++++++---
 c64/kernal/iec_tx_common.s                               | 2 +-
 c64/kernal/iec_tx_eoi.s                                  | 3 +++
 5 files changed, 18 insertions(+), 4 deletions(-)
 rename c64/kernal/{iec_pull_data_release_atn_clock.s => iec_pull_data_release_atn_clk.s} (100%)
 create mode 100644 c64/kernal/iec_release_atn.s

diff --git a/c64/kernal/iec_pull_data_release_atn_clock.s b/c64/kernal/iec_pull_data_release_atn_clk.s
similarity index 100%
rename from c64/kernal/iec_pull_data_release_atn_clock.s
rename to c64/kernal/iec_pull_data_release_atn_clk.s
diff --git a/c64/kernal/iec_release_atn.s b/c64/kernal/iec_release_atn.s
new file mode 100644
index 00000000..194f3856
--- /dev/null
+++ b/c64/kernal/iec_release_atn.s
@@ -0,0 +1,8 @@
+
+iec_release_atn:
+
+	lda CI2PRA
+	and #$FF - BIT_CI2PRA_ATN_OUT    ; release
+	sta CI2PRA
+	rts
+
diff --git a/c64/kernal/iec_tx_command.s b/c64/kernal/iec_tx_command.s
index ca50f4a2..526ae80a 100644
--- a/c64/kernal/iec_tx_command.s
+++ b/c64/kernal/iec_tx_command.s
@@ -57,9 +57,12 @@ iec_tx_command:
 	jsr iec_set_idle
 	jmp kernalerror_DEVICE_NOT_FOUND
 *
-	;; All done - before exiting wait a moment and restore bus to idle state
-	jsr iec_wait20us
-	jsr iec_set_idle
+	;; 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
 
 	clc
 	rts
diff --git a/c64/kernal/iec_tx_common.s b/c64/kernal/iec_tx_common.s
index 73753f72..a9652d6b 100644
--- a/c64/kernal/iec_tx_common.s
+++ b/c64/kernal/iec_tx_common.s
@@ -43,7 +43,7 @@ iec_tx_common_bit_is_sent:
 	;; Pull CLK for 20us again, before sending the next bit
 	;; or performing any other action
 	jsr iec_pull_clk_release_data
-	jsr iec_wait20us
+	jsr iec_wait20us ; XXX this might be an overkill, there is a lot of code besides this wait here - few NOPs might be enough
 
 	;; More bits to send?
 	dex
diff --git a/c64/kernal/iec_tx_eoi.s b/c64/kernal/iec_tx_eoi.s
index 76169af3..5cae87f2 100644
--- a/c64/kernal/iec_tx_eoi.s
+++ b/c64/kernal/iec_tx_eoi.s
@@ -1,6 +1,9 @@
 
 iec_tx_eoi:
 
+	;; Releasing ATN needed due to current iec_tx_command implementation
+	jsr iec_release_atn
+
 	;; Wait at least 256 usec
 	jsr iec_wait100us
 	jsr iec_wait100us