provided screen scroll up unofficial routine

c64/kernal/screen/screen_scroll_delay.s

@@ -0,0 +1,40 @@
+
+//
+// Handles CTRL and NO_SCRL during screen scroll
+//
+
+
+screen_scroll_delay:
+
+#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_delay_done
+
+	ldy #$09
+!:
+	ldx #$FF
+	jsr wait_x_bars
+	dey
+	bne !-
+
+screen_scroll_delay_done:
+	
+	rts