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/vpeek.s
+++ b/libsrc/cx16/vpeek.s
@@ -0,0 +1,19 @@
+;
+; 2019-10-22, Greg King
+;
+; unsigned char fastcall vpeek (unsigned long addr);
+; /* Get a byte from a location in VERA's internal address space. */
+;
+
+        .export         _vpeek
+
+        .import         vset
+        .include        "cx16.inc"
+
+
+_vpeek: php                     ; (vset blocks interrupts)
+        jsr     vset            ; put VERA's address
+        ldx     #>$0000
+        lda     VERA::DATA0     ; read VERA port zero
+        plp
+        rts