add a new log level (trace)

src/engine/engine.h

@@ -190,6 +190,7 @@ class DivEngine {
   bool forceMono;
   bool cmdStreamEnabled;
   bool softLocked;
+  int softLockCount;
   int ticks, curRow, curOrder, remainingLoops, nextSpeed;
   double divider;
   int cycles;
@@ -681,6 +682,8 @@ class DivEngine {
       halted(false),
       forceMono(false),
       cmdStreamEnabled(false),
+      softLocked(0),
+      softLockCount(0),
       ticks(0),
       curRow(0),
       curOrder(0),

src/engine/playback.cpp

@@ -1410,6 +1410,7 @@ void DivEngine::nextBuf(float** in, float** out, int inChans, int outChans, unsi
 
   if (softLocked) {
     if (!isBusy.try_lock()) {
+      logV("audio is soft-locked (%d)\n",softLockCount++);
       return;
     }
   } else {