Lots more comments in sniffer code, a few fixes in sniffer code too.

re/sniffer/snifferitem.cpp

@@ -30,18 +30,37 @@ float SnifferItem::getDelta() const
     return ((float)(mCurrentTime-mLastTime))/1000000;
 }
 
+//Get a data byte by index 0-7 (but not more than the length of the actual frame)
 int SnifferItem::getData(uchar i) const
 {
-    return (i>=mCurrent.len) ? -1 : ((uchar*) &mCurrent.data)[i];
+    return (i >= mCurrent.len) ? -1 : ((uchar*) &mCurrent.data)[i];
 }
 
+//Return whether a given data byte (by index 0-7) has incremented, deincremented, or stayed the same
+//since the last message
+//The If checks first that we aren't past the actual data length
+// then checks whether lastMarker shows that some bits have changed in the previous 200ms cycle
+// then we check if the byte in mNotch has bits set and if it does we say nothing changed (notched out)
 dc SnifferItem::dataChange(uchar i) const
 {
-    if(     i<mCurrent.len &&
-            ((uchar*) &mLastMarker.data)[i] &&
-            !((uchar*) &mNotch)[i] )
+    if (i >= mCurrent.len) return dc::NO;
+
+    uchar notch = ((uchar*) &mNotch)[i];
+    uchar byt = ((uchar*) &mCurrent.data)[i];
+    uchar last = ((uchar*) &mLast.data)[i];
+    uchar lastMark = ((uchar*) &mLastMarker.data)[i];
+    if( lastMark )
     {
-        return ((uchar*) &mCurrent.data)[i] >= ((uchar*) &mLast.data)[i] ? dc::INC : dc::DEINC;
+        if (!notch) //if no notching is set
+            return (byt >= last ? dc::INC : dc::DEINC);
+        else //mNotch contained a bit pattern so use masks and do things more complicated
+        {
+            byt &= ~notch; //mask off bits that were notched
+            if (byt == 0) return dc::NO; //and if result is null then nothing changed (other than maybe notched bits and they don't count)
+            last &= ~notch; //need to mask last too
+            if (last == byt) return dc::NO;
+            return (byt >= last ? dc::INC : dc::DEINC); //then compare the masked copies to see which way the bit(s) went
+        }
     }
 
     return dc::NO;
@@ -52,6 +71,7 @@ int SnifferItem::elapsed() const
     return mTime.elapsed();
 }
 
+//called when a new frame comes in that matches our same ID
 void SnifferItem::update(const CANFrame& pFrame)
 {
     /* copy current to last */
@@ -64,23 +84,28 @@ void SnifferItem::update(const CANFrame& pFrame)
     mCurrentTime = pFrame.timestamp;
 
     /* update marker */
-    mMarker.data |= mLast.data ^ mCurrent.data;
+    //We "OR" our stored marker with the changed bits.
+    //this accumulates changed bits into the marker
+    mMarker.data |= mLast.data ^ mCurrent.data; //XOR causes only changed bits to be 1's
     mMarker.len  |= mLast.len ^ mCurrent.len;
 
     /* restart timeout */
     mTime.restart();
 }
 
+//Called in refresh from the model. Interval about 200ms currently.
+//So, this means the marker only accumulates for 200ms then resets
 void SnifferItem::updateMarker()
 {
     mLastMarker = mMarker;
     mMarker = {0, 0};
 }
 
+//Notch or un-notch this snifferitem / frame
 void SnifferItem::notch(bool pNotch)
 {
     if(pNotch)
-        mNotch |= mLastMarker.data;
+        mNotch |= mLastMarker.data; //add changed bits to notch value
     else
         mNotch = 0;
 }

re/sniffer/sniffermodel.cpp

@@ -154,7 +154,7 @@ void SnifferModel::clear()
     endResetModel();
 }
 
-
+//Called from window with a timer (currently 200ms)
 void SnifferModel::refresh()
 {
     QMap<quint32, SnifferItem*>::iterator i;