text: move: have things moving

too big

textmode/textscroll/move.s

@@ -1,7 +1,13 @@
 
 CH	= $24
 CV	= $25
+BASL	= $28
+BASH	= $29
+SEEDL	= $4E
 
+DRAW_PAGE	= $FF
+
+PAGE0		= $C054
 
 HGR		= $F3E2
 SETTXT		= $FB39
@@ -10,6 +16,7 @@ STORADV		= $FBF0		; store A at (BASL),CH, advancing CH, trash Y
 MON_VTAB	= $FC22		; VTAB to CV
 VTABZ		= $FC24		; VTAB to value in A
 HOME		= $FC58
+WAIT    = $FCA8                 ;; delay 1/2(26+27A+5A^2) us
 
 COUT	= $FDED
 COUT1	= $FDF0
@@ -20,6 +27,9 @@ xpos	= $2100
 
 move:
 	jsr	HGR
+
+	sta	DRAW_PAGE
+
 	jsr	SETTXT
 
 
@@ -30,14 +40,16 @@ next_text:
 	bne	not_new
 
 new_text:
-	lda	#30
+	jsr	random8
+	and	#$1f
+	adc	#$4
 	sta	xpos,X
 
-	txa
+	jsr	random8
+	and	#$f
 	sta	ypos,X
 
 
-
 not_new:
 	lda	xpos,X
 	sta	CH
@@ -46,19 +58,27 @@ not_new:
 
 	jsr	MON_VTAB
 
+	lda	BASH
+	clc
+	adc	DRAW_PAGE
+	sta	BASH
+
 	txa
 	pha
 
 	ldx	#0
-big_loop:
+print_loop:
 	lda	text,X
 
-	bmi	big_done
+	php
 
 	ora	#$80
 	jsr	STORADV
 	inx
-	bne	big_loop
+
+	plp
+
+	bpl	print_loop
 
 big_done:
 
@@ -71,10 +91,61 @@ big_done:
 	cpx	#20
 	bne	next_text
 
-	jsr	HOME
+flip_pages:
+	ldx	#0
+
+	lda     DRAW_PAGE
+	beq	done_page
+	inx
+done_page:
+	ldy	PAGE0,X         ; set display page to PAGE1 or PAGE2
+
+	eor	#$4             ; flip draw page between $400/$800
+        sta	DRAW_PAGE
+
+	clc
+	adc	#$4
+	sta	BASH
+	lda	#$0
+	sta	BASL
+
+clear_screen_outer:
+	ldy	#$f8
+clear_screen_inner:
+	lda	#$A0		; space char
+	sta	(BASL),Y	; 100 101 110 111
+	dey
+	cpy	#$FF
+	bne	clear_screen_inner
+	inc	BASH
+	lda	BASH
+	and	#$3
+	bne	clear_screen_outer
+
+	lda	#$50
+	jsr	WAIT
 
 	jmp	next_frame
 
+
+	;=============================
+        ; random8
+        ;=============================
+        ; 8-bit 6502 Random Number Generator
+        ; Linear feedback shift register PRNG by White Flame
+        ; http://codebase64.org/doku.php?id=base:small_fast_8-bit_prng
+
+random8:
+        lda     SEEDL                                                   ; 2
+        beq     doEor                                                   ; 2
+        asl                                                             ; 1
+        beq     noEor   ; if the input was $80, skip the EOR            ; 2
+        bcc     noEor                                                   ; 2
+doEor:  eor     #$1d                                                    ; 2
+noEor:  sta     SEEDL                                                   ; 2
+	rts
+
+
 text:
 	.byte "HELL",'O'|$80