New get_tv function from Stefan Haubenthal

git-svn-id: svn://svn.cc65.org/cc65/trunk@3230 b7a2c559-68d2-44c3-8de9-860c34a00d81

diff --git a/libsrc/vic20/get_tv.s b/libsrc/vic20/get_tv.s
new file mode 100644 (file)
index 0000000..13c5c42
--- /dev/null
+++ b/libsrc/vic20/get_tv.s
@@ -0,0 +1,33 @@
+;
+; Stefan Haubenthal, 2004-10-07
+; Based on code from Pu-239
+;
+; unsigned char __fastcall__ get_tv (void);
+; /* Return the video mode the machine is using */
+;
+
+       .export         _get_tv
+
+       .include        "vic20.inc"
+
+
+;--------------------------------------------------------------------------
+; _get_tv
+
+.proc  _get_tv
+
+NTSC_LINES = 261
+       ; detect the system
+       lda     #0
+       tax
+@L0:   ldy     VIC_HLINE
+       cpy     #1
+       bne     @L0             ; wait for line 1
+@L1:   ldy     VIC_HLINE
+       beq     @L2             ; line 0 reached -> NTSC
+       cpy     #NTSC_LINES/2+2
+       bne     @L1
+       lda     #1
+@L2:   rts                     ; system detected: 0 for NTSC, 1 for PAL
+
+.endproc