Respect different behaviour of RS and SR flip flops

No more invalid states here.
According to IEC 61131, RS flip flop have dominant reset and SR have
dominant set. This is now implemented.

diff --git a/src/Autopilot/xmlauto.cxx b/src/Autopilot/xmlauto.cxx
index 9c91bff1507f0fa2311efead5e39d23475aaf4f8..189100187dfa28fd20670e606f0e479cfa0dae32 100644 (file)
--- a/src/Autopilot/xmlauto.cxx
+++ b/src/Autopilot/xmlauto.cxx
@@ -918,9 +918,15 @@ void FGXMLAutoLogic::update(double dt)
 }
 
 class FGXMLAutoRSFlipFlop : public FGXMLAutoFlipFlop {
+private:
+  bool _rs;
 public:
   FGXMLAutoRSFlipFlop( SGPropertyNode * node ) :
-    FGXMLAutoFlipFlop( node ) {}
+    FGXMLAutoFlipFlop( node ) {
+      // type exists here, otherwise we were not constructed
+      string val = node->getNode( "type" )->getStringValue();
+      _rs = (val == "RS");
+    }
 
   void updateState( double dt ) {
 
@@ -940,9 +946,13 @@ public:
     // s == false && q == false: no change, keep state
     if( s || r ) {
       bool q = false;
-      if( s ) q = true; // set
-      if( r ) q = false; // reset
-      // s && q: race condition. we let r win
+      if( _rs ) { // RS: reset is dominant
+        if( s ) q = true; // set
+        if( r ) q = false; // reset
+      } else { // SR: set is dominant
+        if( r ) q = false; // reset
+        if( s ) q = true; // set
+      }
       if( inverted ) q = !q;
 
       if ( debug ) cout << "Updating " << get_name() << ":" 
@@ -1374,7 +1384,7 @@ bool FGXMLAutopilot::build( SGPropertyNode_ptr config_props ) {
             string val;
             if( typeNode != NULL ) val = typeNode->getStringValue();
             val = simgear::strutils::strip(val);
-            if( val == "RS" || val =="SR" ) flipFlop      = new FGXMLAutoRSFlipFlop( node );
+            if( val == "RS" || val =="SR" ) flipFlop = new FGXMLAutoRSFlipFlop( node );
             else if( val == "JK" ) flipFlop = new FGXMLAutoJKFlipFlop( node );
             else if( val == "T" ) flipFlop  = new FGXMLAutoTFlipFlop( node );
             else if( val == "D" ) flipFlop  = new FGXMLAutoDFlipFlop( node );