added MEGA65-specific JOYCRSR command

src/basic/basic_commands_04/cmd_joycrsr.s

@@ -0,0 +1,24 @@
+;; #LAYOUT# M65 BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+
+cmd_joycrsr:
+
+	; Make sure we are in MEGA65 native mode
+
+	jsr helper_ensure_native_mode
+
+	; Fetch joystick ID
+
+	jsr fetch_coma_uint8
+	+bcs do_SYNTAX_error
+
+	; Check if joystick ID is valid
+
+	cmp #$03
+	+bcs do_ILLEGAL_QUANTITY_error
+
+	; Set the joystick responsible for moving cursor keys
+
+	sta M65_JOYCRSR    ; XXX consider introducing Kernal call for this 
+	rts

src/basic/basic_commands_04/helper_ensure_native_mode_m65.s

@@ -0,0 +1,10 @@
+;; #LAYOUT# M65 BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+
+helper_ensure_native_mode:
+
+	jsr M65_MODEGET
+	+bcs do_NATIVE_MODE_ONLY_error
+
+	rts