From 353721067470fa1671a0413944dd38b744e9f0bb Mon Sep 17 00:00:00 2001
From: Christian Groessler <chris@groessler.org>
Date: Tue, 27 Oct 2020 22:25:58 +0100
Subject: [PATCH] add waitvsync() for atari and atari5200

---
 doc/atari.sgml               |  1 +
 doc/atari5200.sgml           |  2 +-
 include/atari.h              |  1 +
 include/atari5200.h          |  3 +++
 libsrc/atari/waitvsync.s     | 15 +++++++++++++++
 libsrc/atari5200/waitvsync.s | 15 +++++++++++++++
 6 files changed, 36 insertions(+), 1 deletion(-)
 create mode 100644 libsrc/atari/waitvsync.s
 create mode 100644 libsrc/atari5200/waitvsync.s

diff --git a/doc/atari.sgml b/doc/atari.sgml
index eecd1b803..7fc929f42 100644
--- a/doc/atari.sgml
+++ b/doc/atari.sgml
@@ -332,6 +332,7 @@ See the <url url="funcref.html" name="function reference"> for declaration and u
 <item>_scroll
 <item>_setcolor
 <item>_setcolor_low
+<item>waitvsync
 </itemize>
 
 
diff --git a/doc/atari5200.sgml b/doc/atari5200.sgml
index 00d3dfbd2..032b0ef6c 100644
--- a/doc/atari5200.sgml
+++ b/doc/atari5200.sgml
@@ -77,7 +77,7 @@ Programs containing Atari 5200 specific code may use the <tt/atari5200.h/ header
 <sect1>Atari 5200 specific functions<p>
 
 <itemize>
-<item>TBD.
+<item>waitvsync
 </itemize>
 
 
diff --git a/include/atari.h b/include/atari.h
index 1a00a4c67..b2fca0b0e 100644
--- a/include/atari.h
+++ b/include/atari.h
@@ -227,6 +227,7 @@ extern unsigned char __fastcall__ _getcolor (unsigned char color_reg);
 /* Other screen functions                                                    */
 /*****************************************************************************/
 
+extern void waitvsync (void);                            /* Wait for start of next frame */
 extern int  __fastcall__ _graphics (unsigned char mode); /* mode value same as in BASIC */
 extern void __fastcall__ _scroll (signed char numlines);
                                           /* numlines > 0  scrolls up */
diff --git a/include/atari5200.h b/include/atari5200.h
index d6c2561b2..9662fe98e 100644
--- a/include/atari5200.h
+++ b/include/atari5200.h
@@ -89,5 +89,8 @@ extern void atr5200std_joy[];        /* referred to by joy_static_stddrv[] */
 */
 #define _bordercolor(color) 0
 
+extern void waitvsync (void);
+/* Wait for start of next frame */
+
 /* End of atari5200.h */
 #endif
diff --git a/libsrc/atari/waitvsync.s b/libsrc/atari/waitvsync.s
new file mode 100644
index 000000000..a19b2375d
--- /dev/null
+++ b/libsrc/atari/waitvsync.s
@@ -0,0 +1,15 @@
+;
+; Written by Christian Groessler <chris@groessler.org>
+;
+; void waitvsync (void);
+;
+
+        .include        "atari.inc"
+        .export         _waitvsync
+
+.proc   _waitvsync
+        lda     RTCLOK+2
+@lp:    cmp     RTCLOK+2
+        beq     @lp
+        rts
+.endproc
diff --git a/libsrc/atari5200/waitvsync.s b/libsrc/atari5200/waitvsync.s
new file mode 100644
index 000000000..9a67c6429
--- /dev/null
+++ b/libsrc/atari5200/waitvsync.s
@@ -0,0 +1,15 @@
+;
+; Written by Christian Groessler <chris@groessler.org>
+;
+; void waitvsync (void);
+;
+
+        .include        "atari5200.inc"
+        .export         _waitvsync
+
+.proc   _waitvsync
+        lda     RTCLOK+1
+@lp:    cmp     RTCLOK+1
+        beq     @lp
+        rts
+.endproc