From 6d521967e5c47c16dd13321236f4993527c69d4a Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Fri, 12 Jul 2019 23:09:27 +0200
Subject: [PATCH] implemented CIOUT routine

---
 c64/basic/,aliases.s  |  2 ++
 c64/kernal/,aliases.s |  2 ++
 c64/kernal/ciout.s    | 28 ++++++++++++++++++++++++++++
 c64/kernal/unlsn.s    | 15 ++++++++++++++-
 4 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/c64/basic/,aliases.s b/c64/basic/,aliases.s
index 8a4733fc..a9898755 100644
--- a/c64/basic/,aliases.s
+++ b/c64/basic/,aliases.s
@@ -57,6 +57,8 @@
 	; Keys down clears bits. STOP=bit 7, C= bit 6, SPACE bit 4, CTRL bit 2
 	.alias BUCKYSTATUS $91
 	.alias load_or_verify_flag $93
+	.alias C3PO  $94 ; flag - is BSOUR content valid
+	.alias BSOUR $95 ; serial bus buffered output byte
 	.alias current_file_num $98
 	.alias LDTND $98 ; number of entries in LAT / FAT / SAT tables
 	.alias DFLTN $99
diff --git a/c64/kernal/,aliases.s b/c64/kernal/,aliases.s
index 3f6150db..e5616ae3 100644
--- a/c64/kernal/,aliases.s
+++ b/c64/kernal/,aliases.s
@@ -8,6 +8,8 @@
 	; Keys down clears bits. STOP=bit 7, C= bit 6, SPACE bit 4, CTRL bit 2
 	.alias BUCKYSTATUS $91
 	.alias kernal_load_or_verify_flag $93
+	.alias C3PO  $94 ; flag - is BSOUR content valid
+	.alias BSOUR $95 ; serial bus buffered output byte
 	.alias current_file_num $98
 	.alias LDTND $98 ; number of entries in LAT / FAT / SAT tables
 	.alias DFLTN $99
diff --git a/c64/kernal/ciout.s b/c64/kernal/ciout.s
index e389806a..cc6f666a 100644
--- a/c64/kernal/ciout.s
+++ b/c64/kernal/ciout.s
@@ -1,3 +1,31 @@
 ; Function defined on pp272-273 of C64 Programmers Reference Guide
 ciout:
+
+	;; This routine is documented in 'Compute's Mapping the Commodore 64', page 224
+
+	pha
+	lda C3PO
+	bne ciout_send_byte
+	
+	;; Nothing to send - set buffer as valid, store byte there
+	inc
+	sta C3PO
+	
+	;; Clear carry flag to indicate success
+	clc
+	
+ciout_store_in_buffer:
+
+	;; Store in the buffer data to be sent next, return
+	pla
+	sta BSOUR
 	rts
+	
+ciout_send_byte:
+
+	;; Send previous data
+	lda BSOUR
+	clc ; don't send with EOI
+	jsr iec_tx_byte
+	jmp ciout_store_in_buffer
+
diff --git a/c64/kernal/unlsn.s b/c64/kernal/unlsn.s
index 24180aa5..8dc84fcf 100644
--- a/c64/kernal/unlsn.s
+++ b/c64/kernal/unlsn.s
@@ -2,7 +2,20 @@
 
 unlsn:
 
-	;; This trivial routine is documented in 'Compute's Mapping the Commodore 64', page 224
+	;; This routine is documented in 'Compute's Mapping the Commodore 64', page 224
+	
+	;; First check whether we have something to be sent in the buffer
+	lda C3PO
+	beq +
+	lda BSOUR
+	sec ; send it with EOI
+	jsr iec_tx_byte		; XXX what about the status of this operation?
+	;; Mark the buffer as invalid
+	lda #$00
+	sta C3PO
+*
+	;; Buffer empty send the command
 	lda #$3F
 	jmp iec_tx_command
 
+