New get_tv module from Stefan Haubenthal.

git-svn-id: svn://svn.cc65.org/cc65/trunk@3830 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/nes/Makefile

@@ -54,6 +54,7 @@ OBJS =  _scrsize.o      \
         crt0.o          \
         ctype.o         \
         cvline.o        \
+        get_tv.o        \
         gotox.o         \
         gotoxy.o        \
         gotoy.o         \

libsrc/nes/get_tv.s

@@ -0,0 +1,37 @@
+;
+; Stefan Haubenthal, 2007-01-21
+;
+; unsigned char __fastcall__ get_tv (void);
+; /* Return the video mode the machine is using */
+;
+
+	.include	"nes.inc"
+	.include	"get_tv.inc"
+	.importzp	tmp1, tmp2
+
+;--------------------------------------------------------------------------
+; _get_tv
+
+.proc	_get_tv
+
+	lda	#TV::NTSC	; assume NTSC
+	tax			; clear
+	sta	tmp1
+	sta	tmp2
+	ldy	tickcount
+wait:	cpy	tickcount
+	beq	wait
+	iny			; next tick
+loop:	cpy	tickcount
+	bne	over
+	inc	tmp1
+	bne	loop
+	inc	tmp2
+	bne	loop
+over:	ldy	tmp2
+	cpy	#9
+	bcc	nopal
+	lda	#TV::PAL	; choose PAL
+nopal:	rts
+
+.endproc