Created a target and a library for the Commander X16 prototype computer.

libsrc/cx16/get_tv.s

@@ -0,0 +1,31 @@
+;
+; 2019-09-20, Greg King
+;
+; unsigned char get_tv (void);
+; /* Return the video mode the machine is using. */
+;
+
+        .export         _get_tv
+
+        .include        "cx16.inc"
+
+
+.proc   _get_tv
+        php
+        sei                             ; Don't let interrupts interfere
+
+        ; Point to the video output register.
+
+        stz     VERA::CTRL              ; Use port 0
+        lda     #<VERA::COMPOSER::VIDEO
+        ldx     #>VERA::COMPOSER::VIDEO
+        ldy     #^VERA::COMPOSER::VIDEO
+        sta     VERA::ADDR
+        stx     VERA::ADDR+1
+        sty     VERA::ADDR+2
+
+        lda     VERA::DATA0
+        plp                             ; Re-enable interrupts
+        and     #$07                    ; Get the type of output signal
+        rts
+.endproc