From c84091291ae1f9eabbe6c1887e0f5473ddc58dbb Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Sun, 5 Jan 2020 18:06:25 +0100
Subject: [PATCH] screen scroll rework finished

---
 c64/kernal/screen/screen_scroll_up.s | 200 ++++++++++-----------------
 1 file changed, 71 insertions(+), 129 deletions(-)

diff --git a/c64/kernal/screen/screen_scroll_up.s b/c64/kernal/screen/screen_scroll_up.s
index d50f2304..74cfdf82 100644
--- a/c64/kernal/screen/screen_scroll_up.s
+++ b/c64/kernal/screen/screen_scroll_up.s
@@ -6,18 +6,6 @@
 
 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
 
@@ -62,14 +50,76 @@ screen_scroll_up_delay_done:
 	lda #$80
 	sta LDTBL+24
 
-	// Now, we need to scroll both screen memory and color memory
+	// Preserve SAL and EAL
 
+	lda SAL+0
+	pha
+	lda SAL+1
+	pha	
+	lda EAL+0
+	pha
+	lda EAL+1
+	pha
 
+	// Now, we need to scroll both screen memory and color memory; first create start/end pointers
 
-	// YYY implement
+	lda HIBASE
+	sta SAL+1
+	sta EAL+1
 
+	lda #>$D800
+	sta PNT+1
+	sta USER+1
 
+	lda #$00
+	sta EAL+0
+	sta USER+0
+	lda #40
+	sta SAL+0
+	sta PNT+0
 
+	// Now copy, SAL->EAL, PNT->USER, in a loop
+
+	ldy #$00
+
+screen_scroll_up_loop:
+
+	lda (SAL),  y
+	sta (EAL),  y
+	lda (PNT),  y
+	sta (USER), y
+
+	// Check if this was the last byte (last destination byte for color copy is #DBBF)
+
+	cpy #$BF
+	bne !+                             // definitely not the last byte
+	lda USER+1
+	cmp #$DB
+	beq screen_scroll_up_loop_done
+!:
+	// Increment .Y, possibly advance pointers
+
+	iny
+	bne screen_scroll_up_loop
+
+	inc SAL+1
+	inc EAL+1
+	inc USER+1
+	inc PNT+1
+	bne screen_scroll_up_loop          // branch alwayys
+
+screen_scroll_up_loop_done:
+
+	// Restore SAL and EAL
+	
+ 	pla
+ 	sta EAL+1
+ 	pla
+ 	sta EAL+0
+ 	pla
+ 	sta SAL+1
+ 	pla
+ 	sta SAL+0
 
 	// Clear the newly introduced line
 
@@ -83,22 +133,15 @@ screen_scroll_up_delay_done:
 	// If the first line is linked, scroll once more
 
 	bit LDTBL+0
-	bpl screen_scroll_up_next
+#if CONFIG_KEYBOARD_C128 || CONFIG_KEYBOARD_C65
+	bpl_far screen_scroll_up
+#else
+	bpl screen_scroll_up
+#endif
 
-	// Restore SAL and EAL
-	
- 	pla
- 	sta EAL+1
- 	pla
- 	sta EAL+0
- 	pla
- 	sta SAL+1
- 	pla
- 	sta SAL+0
+ 	// Recalculate PNT and USER
 
- 	// Return
-
-	rts
+	jmp screen_calculate_PNT_USER
 
 
 
@@ -135,105 +178,4 @@ is_last_line:
 
 	// FALLTHROUGH to screen_scroll_up
 
-
-
-scroll_screen_up:
-
-	// Preserve EAL
-	lda EAL+0
-	pha
-	lda EAL+1
-	pha	
-
-	// Now scroll the whole screen up either one or two lines
-	// based on whether the first screen line is linked or not.
-
-	// Get pointers to start of screen + colour RAM
-	lda HIBASE
-	sta PNT+1
-	sta SAL+1
-	lda #>$D800
-	sta USER+1
-	sta EAL+1
-	lda #$00
-	sta PNT+0
-	sta USER+0
-	
-	//  Get pointers to screen/colour RAM source
-	lda LDTBL+0
-	bmi !+
-	lda #40
-	.byte $2C 		// BIT $nnnn to skip next instruction
-!:
-	lda #80
-	sta SAL+0
-	sta EAL+0
-
-	//  Copy first three pages
-	ldy #$00
-	ldx #3
-scroll_copy_loop:
-	lda (EAL),y
-	sta (USER),y
-	lda (SAL),y
-	sta (PNT),y
-
-	iny
-	bne scroll_copy_loop
-
-	inc SAL+1
-	inc PNT+1
-	inc EAL+1
-	inc USER+1
-	dex
-	bne scroll_copy_loop
-
-	// Copy last partial page
-	// We need to copy 1000-(3*256)-line length
-	// = 232 - line length
-	lda SAL+0
-	lda #232
-	sec
-	sbc SAL+0
-	tax
-scroll_copy_loop2:
- 	lda (EAL),y
- 	sta (USER),y
- 	lda (SAL),y
- 	sta (PNT),y
- 	iny
- 	dex
- 	bne scroll_copy_loop2
-
- 	// Restore EAL
- 	pla
- 	sta EAL+1
- 	pla
- 	sta EAL+0
-
-	// Fill in scrolled up area
-	ldx SAL+0
-scroll_copy_loop3:
-	lda COLOR
-	sta (USER),y
-	lda #$20
-	sta (PNT),y
-	iny
-	dex
-	bne scroll_copy_loop3
-
-	// Shift line linkage list
-	ldy #0
-	ldx #24
-link_copy:
-	lda LDTBL+1,y
-	sta LDTBL+0,y
-	iny
-	dex
-	bne link_copy
-	// Clear line link flag of last line
-	stx LDTBL+24
-
-	// Restore correct line pointers
-	jmp screen_calculate_line_pointer
 */
\ No newline at end of file