size-optimized screen clearing

c64/kernal/screen/clear_screen_real.s

@@ -7,60 +7,4 @@
 
 
 clear_screen_real:
-
+	rts
-	// Clear the line link table - cheecked on original ROMs,
-	// the highest bit set means that the line is NOT a logical
-	// continuation of the previous one
-
-	lda #$80
-	ldy #24	
-!:
-	sta LDTBL,y
-	dey
-	bpl !-
-
-	// YYY flow can probably be size-optimized by calling screen_clear_line in a loop
-
-	// Clear screen character RAM. Unfortunately, the HIBASE value is not on the zero page,
-	// we will reuse PNT (it will be overridden in a moment nevertheless) as the pointer
-
-	iny                                // sets .Y to 0
-	sty PNT+0
-	lda HIBASE
-	sta PNT+1	
-
-	ldx #$03                           // countdown for pages to update
-
-clear_screen_loop:
-
-	ldy #$00
-	lda #$20                           // space character screen code
-!:
-	sta (PNT),y
-	iny
-	cpy #250                           // clear 250 bytes only, do not cross 1000 bytes barrier
-	bne !-
-
-	lda PNT+0
-	clc
-	adc #250
-	sta PNT+0
-	bcc !+
-	inc PNT+1
-!:
-	dex
-	bpl clear_screen_loop
-
-	// Now clear the colour RAM - .Y is now 250, make use of this fact
-
-	lda COLOR
-!:
-	sta $D800 - 1 + 250 * 0, y
-	sta $D800 - 1 + 250 * 1, y
-	sta $D800 - 1 + 250 * 2, y
-	sta $D800 - 1 + 250 * 3, y
-	dey
-	bne !-
-
-	// Fall to cursor home routine
-	jmp cursor_home

c64/kernal/screen/e544.clear_screen.jmp.s

@@ -1,11 +0,0 @@
-
-//
-// Clear screen and initialise line link table, described in:
-//
-// - [CM64] Computes Mapping the Commodore 64 - pages 215-216
-//
-
-
-clear_screen:
-
-    jmp clear_screen_real

c64/kernal/screen/e544.clear_screen.s

@@ -0,0 +1,30 @@
+
+//
+// Clear screen and initialise line link table, described in:
+//
+// - [CM64] Computes Mapping the Commodore 64 - pages 215-216
+//
+
+
+clear_screen:
+
+	// Clear the line link table - cheecked on original ROMs,
+	// the highest bit set means that the line is NOT a logical
+	// continuation of the previous one
+
+	lda #$80
+	ldy #24	
+!:
+	sta LDTBL,y
+	dey
+	bpl !-
+
+	// Clear all the rows
+	ldx #24
+!:
+	jsr screen_clear_line
+	dex
+	bpl !-
+
+	// Fall to cursor home routine
+	jmp cursor_home