started work on screen scroll

c64/kernal/screen/screen_scroll_up.s

@@ -0,0 +1,239 @@
+
+//
+// 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:
+	rts
+
+screen_scroll_up_if_on_last_line:
+
+	// Colour RAM is always in fixed place, so is easiest
+	// to use to check if we are on the last line.
+	// The last line is at $D800 + 24*40 = $DBC0
+	lda USER+1
+	cmp #>$DBC0
+	bne not_last_line
+
+	lda USER+0
+	cmp #<$DBC0
+	beq is_last_line
+
+	jsr screen_get_current_line_logical_length
+	clc
+	adc USER+0
+	cmp #<$DBE7-1
+	bcc not_last_line
+
+is_last_line:
+
+	dec TBLX
+
+	// 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
+*/