small cleanup in BASIC, improved cartridge compatibility

c64/basic/init/basic_cold_start_internal.s

@@ -31,6 +31,11 @@ basic_cold_start_internal:
 	lda #>do_ILLEGAL_QUANTITY_error
 	sta USRADD+1
 
+	// Clear the BRK location address
+	lda #$00
+	sta CMP0+0
+	sta CMP0+1
+
 	// Print startup messages
 	jsr INITMSG
 

c64/basic/init/initmsg_real.s

@@ -5,6 +5,10 @@
 
 initmsg_real:
 
+	// Clear the screen first, some cartridges (like IEEE-488) leeave a mess on the screen
+	lda #147
+	jsr JCHROUT
+
 #if CONFIG_BANNER_SIMPLE
 
 	lda #<startup_banner