Implemented clrscr routine for C1P

libsrc/c1p/c1p.inc

@@ -0,0 +1,3 @@
+
+SCRNBASE       := $D000        ; Base of video RAM
+VIDEORAMSIZE   := $0400        ; Size of C1P video RAM (1 kB)

libsrc/c1p/clrscr.s

@@ -0,0 +1,23 @@
+;
+; void clrscr (void);
+;
+        .export         _clrscr
+        .include        "c1p.inc"
+
+; Adapted from the Challenger Character Graphics
+; Reference Manual, "2.3.3 MACHINE LANGUAGE SCREEN CLEAR"
+; This is self-modifying code!
+BANKS = VIDEORAMSIZE / $100
+
+_clrscr:	LDA #$20 ;' '
+		LDY #BANKS
+		LDX #$00
+STALOC:		STA SCRNBASE,X
+		INX
+		BNE STALOC
+		INC STALOC+2
+		DEY
+		BNE STALOC
+		LDA #>(SCRNBASE) ; load high byte
+		STA STALOC+2     ; restore base address
+		RTS