From 44df124fc7b1d3186a1cef9a692400ca02b8c870 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Sun, 5 Jan 2020 17:27:37 +0100
Subject: [PATCH] started work on screen scroll

---
 c64/kernal/iec/iec_wait1ms.s                  |   6 +-
 .../screen/screen_advance_to_next_line.s      |   3 +-
 ...p_if_on_last_line.s => screen_scroll_up.s} | 107 +++++++++++++++++-
 3 files changed, 108 insertions(+), 8 deletions(-)
 rename c64/kernal/screen/{screen_scroll_up_if_on_last_line.s => screen_scroll_up.s} (59%)

diff --git a/c64/kernal/iec/iec_wait1ms.s b/c64/kernal/iec/iec_wait1ms.s
index 4e81fb14..4e05f18e 100644
--- a/c64/kernal/iec/iec_wait1ms.s
+++ b/c64/kernal/iec/iec_wait1ms.s
@@ -16,9 +16,8 @@ iec_wait1ms:
 	ldx #18 // we probably won't start with the beginning of raster
 
 #endif // CONFIG_IEC
-#if CONFIG_IEC || (!CONFIG_TAPE_NO_MOTOR_CONTROL && (CONFIG_TAPE_TURBO || CONFIG_TAPE_NORMAL))
 
-wait_x_bars: // additional entry point for tape support
+wait_x_bars: // additional entry point for delayy in screen and tape support
              // has to preserve .Y and put .X to 0
 
 	lda VIC_RASTER
@@ -32,6 +31,3 @@ wait_x_bars: // additional entry point for tape support
 iec_wait_rts: // dummy RTS, for very short waits
 
 	rts
-
-
-#endif
diff --git a/c64/kernal/screen/screen_advance_to_next_line.s b/c64/kernal/screen/screen_advance_to_next_line.s
index 0a8f2baa..15a56d60 100644
--- a/c64/kernal/screen/screen_advance_to_next_line.s
+++ b/c64/kernal/screen/screen_advance_to_next_line.s
@@ -4,12 +4,11 @@ screen_advance_to_next_line:
 
 	// Check if we are at the bottom of the screen
 	ldy TBLX
-	cpy #$24
+	cpy #24
 	bne !+
 
 	// We need to scroll the screen up
 	jsr screen_scroll_up
-	skip_2_bytes_trash_nvz
 !:
 	inc TBLX
 
diff --git a/c64/kernal/screen/screen_scroll_up_if_on_last_line.s b/c64/kernal/screen/screen_scroll_up.s
similarity index 59%
rename from c64/kernal/screen/screen_scroll_up_if_on_last_line.s
rename to c64/kernal/screen/screen_scroll_up.s
index 42888bca..d50f2304 100644
--- a/c64/kernal/screen/screen_scroll_up_if_on_last_line.s
+++ b/c64/kernal/screen/screen_scroll_up.s
@@ -1,7 +1,110 @@
 
+//
+// Scroll the whole screen up by 1 logical line
+//
+
+
 screen_scroll_up:
+
+	// Preserve SAL and EAL
+
+	lda SAL+0
+	pha
+	lda SAL+1
+	pha	
+	lda EAL+0
+	pha
+	lda EAL+1
+	pha	
+
+screen_scroll_up_next:
+
+#if CONFIG_KEYBOARD_C128 || CONFIG_KEYBOARD_C65
+
+	// Do not scroll if NO_SCRL is pressed and interrupts are enabled
+!:
+	php
+	pla
+	and #%00000010
+	bne !+                             // branch if IRQs disabled, we cannot detect NO_SCRL status
+
+	lda SHFLAG
+	and #KEY_FLAG_NO_SCRL
+	bne !-
+!:
+#endif
+
+	// Check if CTRL key pressed - if so, perform a delay
+
+	lda SHFLAG
+	and #KEY_FLAG_CTRL
+	beq screen_scroll_up_delay_done
+
+	ldy #$03
+!:
+	ldx #$FF
+	jsr wait_x_bars
+	dey
+	bne !-
+
+screen_scroll_up_delay_done:
+
+	// First scroll the LDTBL (line link table)
+
+	ldy #$00
+!:
+	lda LDTBL+1, y
+	sta LDTBL+0, y
+	iny
+	cpy #24
+	bne !-
+
+	lda #$80
+	sta LDTBL+24
+
+	// Now, we need to scroll both screen memory and color memory
+
+
+
+	// YYY implement
+
+
+
+
+	// Clear the newly introduced line
+
+	ldx #24
+	jsr screen_clear_line
+
+	// Decrement the current physical line number
+
+	dec TBLX
+
+	// If the first line is linked, scroll once more
+
+	bit LDTBL+0
+	bpl screen_scroll_up_next
+
+	// Restore SAL and EAL
+	
+ 	pla
+ 	sta EAL+1
+ 	pla
+ 	sta EAL+0
+ 	pla
+ 	sta SAL+1
+ 	pla
+ 	sta SAL+0
+
+ 	// Return
+
 	rts
 
+
+
+
+
+
 /* YYY disabled for rework, add CTRL and NO_SCROLL support
 
 not_last_line:
@@ -30,7 +133,9 @@ is_last_line:
 
 	dec TBLX
 
-	// FALLTHROUGH
+	// FALLTHROUGH to screen_scroll_up
+
+
 
 scroll_screen_up: