From b965e035f92f7cd1c705824b30a87ec2f6f2b948 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Wed, 7 Oct 2020 16:02:07 +0200
Subject: [PATCH] documentation update, small Ultimate 64 code tweaks

---
 CONFIG.md                                    |  2 +-
 src/basic/basic_commands_01/cmd_fast_slow.s  |  3 +--
 src/kernal/iec_fast/jiffydos_load.s          |  8 +++----
 src/kernal/iec_fast/jiffydos_prepare.s       | 11 +++++-----
 src/kernal/iec_fast/jiffydos_preserve_bits.s | 23 ++++++++++++++++++++
 5 files changed, 33 insertions(+), 14 deletions(-)
 create mode 100644 src/kernal/iec_fast/jiffydos_preserve_bits.s

diff --git a/CONFIG.md b/CONFIG.md
index 064877d1..68fa3e88 100644
--- a/CONFIG.md
+++ b/CONFIG.md
@@ -139,7 +139,7 @@ Needs about 430 bytes in KERNAL segment. If unsure - enable.
 
 ### `IEC_JIFFYDOS_BLANK`
 
-Causes screen blanking during JiffyDOS file loading to increase performance.
+Causes screen blanking during JiffyDOS file loading to increase performance. On Ultimate 64 motherboard, if possible, screen blanking is substituted by disabling badlines.
 
 ## Tape deck
 
diff --git a/src/basic/basic_commands_01/cmd_fast_slow.s b/src/basic/basic_commands_01/cmd_fast_slow.s
index 3faff194..7b7adb86 100644
--- a/src/basic/basic_commands_01/cmd_fast_slow.s
+++ b/src/basic/basic_commands_01/cmd_fast_slow.s
@@ -20,7 +20,6 @@ cmd_slow:
 
 cmd_slow_fast_common:
 
-	sta U64_TURBOBIT                   ; only bit 0 matters
 	sta U64_TURBOCTL
 	rts
 
@@ -29,7 +28,7 @@ cmd_fast:
 	lda #$0F                           ; for U64_TURBOCTL - badlines, 48MHz
 	sta SCPU_SPEED_TURBO               ; any value will do
 
-	bne cmd_slow_fast_common           ; bramnch always
+	bne cmd_slow_fast_common           ; branch always
 
 } else ifdef CONFIG_PLATFORM_COMMODORE_64 {
 
diff --git a/src/kernal/iec_fast/jiffydos_load.s b/src/kernal/iec_fast/jiffydos_load.s
index 7ff2392d..04251a54 100644
--- a/src/kernal/iec_fast/jiffydos_load.s
+++ b/src/kernal/iec_fast/jiffydos_load.s
@@ -29,6 +29,8 @@ jiffydos_load:
 
 !ifdef CONFIG_MB_U64 {
 
+	; XXX implement for non-blank mode, use jiffydos_prepare_no_preserve_bits
+
 	; Check if turbo register is available
 	lda U64_TURBOCTL
 	cmp #$FF
@@ -52,10 +54,7 @@ jiffydos_load:
 	jsr screen_off
 @2:
 	; Preserve 3 lowest bits of CIA2_PRA  XXX deduplicate this
-
-	lda CIA2_PRA
-	and #%00000111
-	sta C3PO
+	jsr jiffydos_preserve_bits
 
 } else {
 
@@ -66,7 +65,6 @@ jiffydos_load:
 @2:
 
 }
-
 	; A trick to shorten EAL update time
 	ldy #$FF
 
diff --git a/src/kernal/iec_fast/jiffydos_prepare.s b/src/kernal/iec_fast/jiffydos_prepare.s
index 244fb5f0..cf939906 100644
--- a/src/kernal/iec_fast/jiffydos_prepare.s
+++ b/src/kernal/iec_fast/jiffydos_prepare.s
@@ -12,12 +12,11 @@
 
 jiffydos_prepare:
 
-	; We need to preserve 3 lowest bits of CIA2_PRA, they contain important
-	; data - fortunately, the bits are never changed by external devices
-	; Use C3PO for this, as afterwards we have to set there 0 nevertheless
-	lda CIA2_PRA
-	and #%00000111
-	sta C3PO
+	jsr jiffydos_preserve_bits
+
+	; FALLTROUGH
+
+jiffydos_prepare_no_preserve_bits:
 
 	; Hide sprites; JiffyDOS timing regime is very strict, before transmitting
 	; anything we need to make sure nothing will steal the cycles
diff --git a/src/kernal/iec_fast/jiffydos_preserve_bits.s b/src/kernal/iec_fast/jiffydos_preserve_bits.s
new file mode 100644
index 00000000..8a18019d
--- /dev/null
+++ b/src/kernal/iec_fast/jiffydos_preserve_bits.s
@@ -0,0 +1,23 @@
+;; #LAYOUT# STD *        #TAKE
+;; #LAYOUT# *   KERNAL_0 #TAKE
+;; #LAYOUT# *   *        #IGNORE
+
+;
+; JiffyDOS transfer preparation routine
+;
+
+
+!ifdef CONFIG_IEC_JIFFYDOS {
+
+
+jiffydos_preserve_bits:
+
+	; We need to preserve 3 lowest bits of CIA2_PRA, they contain important
+	; data - fortunately, the bits are never changed by external devices
+	; Use C3PO for this, as afterwards we have to set there 0 nevertheless
+	lda CIA2_PRA
+	and #%00000111
+	sta C3PO
+
+	rts
+}