Added VERA peek() and poke() to the cx16 library.

They simplify C programs' direct access to VERA's internal address space.
2019-10-24 05:15:42 -04:00
parent 1074d35a15
commit 9fa90e2265
4 changed files with 74 additions and 5 deletions
--- a/libsrc/cx16/vset.s
+++ b/libsrc/cx16/vset.s
@@ -0,0 +1,20 @@
+;
+; 2019-10-22, Greg King
+;
+; Set the __far__ address that VERA will use for data access.
+; This is a support function for the fastcall functions vpeek() and vpoke().
+;
+
+        .export         vset
+
+        .importzp       sreg
+        .include        "cx16.inc"
+
+
+vset:   ldy     sreg
+        sei                     ; don't let interrupt handlers interfere
+        stz     VERA::CTRL      ; set address for VERA's data port zero
+        sta     VERA::ADDR
+        stx     VERA::ADDR+1
+        sty     VERA::ADDR+2
+        rts