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

They simplify C programs' direct access to VERA's internal address space.

include/cx16.h

@@ -144,9 +144,10 @@ struct __emul {
     unsigned char       debug;          /* Boolean: debugging enabled */
     unsigned char       vera_action;    /* Boolean: displaying VERA activity */
     unsigned char       keyboard;       /* Boolean: displaying typed keys */
-    unsigned char       echo;           /* Boolean: Kernal output echoed to host */
+    unsigned char       echo;           /* How Kernal output should be echoed to host */
     unsigned char       save_on_exit;   /* Boolean: save SD card when quitting */
-    unsigned char       unused[0xD - 0x5];
+    unsigned char       gif_method;     /* How GIF movie is being recorded */
+    unsigned char       unused[0xD - 0x6];
     unsigned char       keymap;         /* Keyboard layout number */
        const char       detect[2];      /* "16" if running on x16emu */
 };
@@ -173,16 +174,24 @@ signed char get_ostype (void);
 ** Positive -- release build
 */
 
-void __fastcall__ set_tv (unsigned char);
-/* Set the video mode the machine will use.
+void __fastcall__ set_tv (unsigned char type);
+/* Set the video type that the machine will use.
 ** Call with a TV_xx constant.
 */
 
-unsigned char __fastcall__ videomode (unsigned char Mode);
+unsigned char __fastcall__ videomode (unsigned char mode);
 /* Set the video mode, return the old mode. Call with one of the VIDEOMODE_xx
 ** constants.
 */
 
+unsigned char __fastcall__ vpeek (unsigned long addr);
+/* Get a byte from a location in VERA's internal address space. */
+
+void __fastcall__ vpoke (unsigned char data, unsigned long addr);
+/* Put a byte into a location in VERA's internal address space.
+** (addr is second instead of first for the sake of code efficiency.)
+*/
+
 
 
 /* End of cX16.h */

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

libsrc/cx16/vpoke.s

@@ -0,0 +1,21 @@
+;
+; 2019-10-22, Greg King
+;
+; void fastcall vpoke (unsigned char data, unsigned long addr);
+; /* Put a byte into a location in VERA's internal address space.
+; ** (addr is second instead of first for the sake of code efficiency.)
+; */
+;
+
+        .export         _vpoke
+
+        .import         vset, popa
+        .include        "cx16.inc"
+
+
+_vpoke: php                     ; (vset blocks interrupts)
+        jsr     vset            ; put VERA's address
+        jsr     popa
+        sta     VERA::DATA0     ; write data to VERA port zero
+        plp
+        rts

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