Documentation.

src/emucore/tia/frame-manager/FrameLayoutDetector.cxx

@@ -22,10 +22,17 @@
  * Misc. numeric constants used in the algorithm.
  */
 enum Metrics: uInt32 {
+  // ideal frame heights
   frameLinesNTSC            = 262,
   frameLinesPAL             = 312,
+
+  // number of scanlines to wait for vsync to start and stop (exceeding ideal frame height)
   waitForVsync              = 100,
+
+  // tolerance window around ideal frame size for TV mode detection
   tvModeDetectionTolerance  = 20,
+
+  // these frames will not be considered for detection
   initialGarbageFrames      = TIAConstants::initialGarbageFrames
 };
 

src/emucore/tia/frame-manager/YStartDetector.cxx

@@ -22,15 +22,27 @@
  * Misc. numeric constants used in the algorithm.
  */
 enum Metrics: uInt32 {
+  // ideal world frame sizes
   frameLinesNTSC            = 262,
   frameLinesPAL             = 312,
+
+  // the ideal vblank zone
   vblankNTSC                = 37,
   vblankPAL                 = 45,
+
+  // number of scanlines to wait for vsync to start (exceeding after the ideal frame size) and stop
   waitForVsync              = 50,
-  tvModeDetectionTolerance  = 20,
+
+  // max lines underscan
   maxUnderscan              = 10,
+
+  // max lines deviations from detected ystart before we switch back to floating
   maxVblankViolations       = 2,
+
+  // switch to fixed mode after this number of stable frames (+1)
   minStableVblankFrames     = 1,
+
+  // no transitions to fixed mode will happend during those
   initialGarbageFrames      = TIAConstants::initialGarbageFrames
 };
 

src/emucore/tia/frame-manager/YStartDetector.hxx

@@ -32,50 +32,116 @@ class YStartDetector: public AbstractFrameManager {
 
   public:
 
+    /**
+     * Getter for the detected ystart value
+     */
     uInt32 detectedYStart() const;
 
+    /**
+     * We require frame layout to be set from outside.
+     */
     void setLayout(FrameLayout layout) override { this->layout(layout); }
 
   protected:
 
+    /**
+     * We need to track vsync changes.
+     */
     void onSetVsync() override;
 
+    /**
+     * Reset hook.
+     */
     void onReset() override;
 
+    /**
+     * The workhorse.
+     */
     void onNextLine() override;
 
   private:
 
+    /**
+     * Our various states.
+     */
     enum State {
+      // Wait for vsync on
       waitForVsyncStart,
+
+      // Wait for vsync off
       waitForVsyncEnd,
+
+      // Wait for the visible frame to start
       waitForFrameStart
     };
 
+    /**
+     * Have we settled on a frame start?
+     */
     enum VblankMode {
+      // We have settled on a frame start and have some hysteresis before we return to floating
       locked,
+
+      // We are actively looking for the frame to start
       floating
     };
 
   private:
 
+    /**
+     * Side effects for state transitions.
+     */
     void setState(State state);
 
+    /**
+     * Perform detection and decide whether the frame starts now.
+     */
     bool shouldTransitionToFrame();
 
   private:
 
+    /**
+     * State.
+     */
     State myState;
 
+    /**
+     * locked / floating
+     */
     VblankMode myVblankMode;
 
+    /**
+     * Counts the scanlines that we wait for vsync to start.
+     */
     uInt32 myLinesWaitingForVsyncToStart;
 
+    /**
+     * The number of lines we are currently waiting for the frame to start (and vblank to end).
+     */
     uInt32 myCurrentVblankLines;
+
+    /**
+     * The number of vblank lines on the last frame.
+     */
     uInt32 myLastVblankLines;
+
+    /**
+     * Count "vblank violations" in fixed mode (the number of consecutive frames where ystart
+     * differs from the previously detected value). Once a trip point is reached, we transition
+     * back to floating mode.
+     */
     uInt32 myVblankViolations;
+
+    /**
+     * The number of frames in floating mode with stable ystart. Once a trip point is reacted,
+     * we transition to fixed mode
+     */
     uInt32 myStableVblankFrames;
 
+    /**
+     * Tracks deviations from the determined ystart value during a fixed mode frame in order to
+     * avoid double counting.
+     */
     bool myVblankViolated;
 
   private: