more comments, slightly safer IEC

c64/kernal/fda3.ioinit.s

@@ -1,4 +1,13 @@
-; Function defined on pp272-273 of C64 Programmers Reference Guide
+
+;;
+;; Official Kernal routine, described in:
+;;
+;; - [RG64] C64 Programmer's Reference Guide   - page 285
+;; - [CM64] Compute's Mapping the Commodore 64 - page 238
+;;
+;; CPU registers that has to be preserved (see [RG64]): none
+;;
+
 ioinit:
 
 	; Set $00/$01 port mode and value