From 2e9bada1f20b645ea94343adaf03d85da15a1d45 Mon Sep 17 00:00:00 2001
From: baktrasf <zylon@post.cz>
Date: Wed, 23 Dec 2020 23:35:09 +0100
Subject: [PATCH] Atari 5200 OS header refinements

---
 doc/atari5200.sgml     | 10 ++++++++++
 include/_atari5200os.h | 18 +++++++++---------
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/doc/atari5200.sgml b/doc/atari5200.sgml
index 032b0ef6c..2ec3d08f0 100644
--- a/doc/atari5200.sgml
+++ b/doc/atari5200.sgml
@@ -73,7 +73,17 @@ Special locations:
 
 Programs containing Atari 5200 specific code may use the <tt/atari5200.h/ header file.
 
+This also includes access to operating system locations (e.g. hardware shadow registers) by a structure called
+"<tt/OS/".
+The names are the usual ones you can find in system reference manuals. Example:
 
+<tscreen><verb>
+...
+    OS.sdmctl = 0x00;                       // screen off
+    OS.color4 = 14;                         // white frame
+... tics = OS.rtclok[1]                     // get ticks
+</verb></tscreen>
+ 
 <sect1>Atari 5200 specific functions<p>
 
 <itemize>
diff --git a/include/_atari5200os.h b/include/_atari5200os.h
index 77ccf14ed..db0f7f0c9 100644
--- a/include/_atari5200os.h
+++ b/include/_atari5200os.h
@@ -49,12 +49,12 @@ struct __os {
     unsigned char pcolr1;            // = $09       PM color 1
     unsigned char pcolr2;            // = $0A       PM color 2
     unsigned char pcolr3;            // = $0B       PM color 3
-    unsigned char color0;            // = $0C       PF Color 0
-    unsigned char color1;            // = $0D       PF Color 1
-    unsigned char color2;            // = $0E       PF Color 2
-    unsigned char color3;            // = $0F       PF Color 3
-    unsigned char color4;            // = $10       PF Color 4
-    unsigned char __filler[0xEF];    // = $11-$FF   Filler
+    unsigned char color0;            // = $0C       PF color 0
+    unsigned char color1;            // = $0D       PF color 1
+    unsigned char color2;            // = $0E       PF color 2
+    unsigned char color3;            // = $0F       PF color 3
+    unsigned char color4;            // = $10       PF color 4
+    unsigned char _free_1[0xEF];     // = $11-$FF   User space
     
     /*Stack*/
     unsigned char stack[0x100];      // = $100-$1FF Stack
@@ -65,9 +65,9 @@ struct __os {
     void (*vvblkd)(void);            // = $204      Deferred VBI vector
     void (*vdslst)(void);            // = $206      DLI vector
     void (*vkeybd)(void);            // = $208      Keyboard IRQ vector
-    void (*vkeypd)(void);            // = $20A      Keypad continue vector
+    void (*vkeypd)(void);            // = $20A      Keyboard continuation vector
     void (*vbrkky)(void);            // = $20C      Break key interrupt vector
-    void (*vbreak)(void);            // = $20E      Break instruction interrupt vector
+    void (*vbreak)(void);            // = $20E      BRK instruction interrupt vector
     void (*vserin)(void);            // = $210      Serial input ready vector
     void (*vseror)(void);            // = $212      Serial output data needed vector
     void (*vseroc)(void);            // = $214      Serial output completed vector
@@ -77,4 +77,4 @@ struct __os {
     
 };
 
-#endif
\ No newline at end of file
+#endif