more work on external BASIC ROM support

c64/basic/board_m65/mega65_map_helpers.s

@@ -0,0 +1,28 @@
+// #LAYOUT# M65 BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// ROM mapping routines for Mega65
+//
+
+// Available memory maps:
+// - NORMAL  - nothing mapped in (taken from Kernal)
+// - BASIC_1 - for calling KERNAL_1 segment code
+
+
+map_BASIC_1:
+
+	php
+	pha
+	phx
+	phy
+	phz
+
+	lda #$00
+	tay
+	taz
+
+	lda #$20
+	ldx #$42    // 0x4000 <- map 8KB from 0x22000
+
+	jmp map_end