Adds debug log to the common DccDecoder class. (#619)

* Adds debug log to the common DccDecoder class.

* Switches LogRing to assign values forward instead of backward.
It is confusing and unexpected to look at an array in gdb and
see the values in the wrong order.

src/freertos_drivers/common/DccDecoder.hxx

@@ -198,6 +198,10 @@ private:
         inputData_->flush();
     };
 
+#ifdef DCC_DECODER_DEBUG
+    LogRing<uint16_t, 256> debugLog_;
+#endif
+
     typedef DCCPacket input_data_type;
     DeviceBuffer<DCCPacket> *inputData_ {
         DeviceBuffer<DCCPacket>::create(Module::Q_SIZE)};
@@ -291,6 +295,11 @@ __attribute__((optimize("-O3"))) void DccDecoder<Module>::interrupt_handler()
         // Debug::DccDecodeInterrupts::toggle();
         uint32_t raw_new_value = Module::get_capture_counter();
         uint32_t old_value = lastTimerValue_;
+#ifdef DCC_DECODER_DEBUG
+        debugLog_.add(0);
+        debugLog_.add(old_value);
+        debugLog_.add(raw_new_value);
+#endif
         if (raw_new_value > old_value) {
             // Timer has overflowed.
             if (nextSample_ < old_value) {
@@ -311,6 +320,9 @@ __attribute__((optimize("-O3"))) void DccDecoder<Module>::interrupt_handler()
             nextSample_ -= Module::SAMPLE_PERIOD_CLOCKS;
         }
         uint32_t new_value = old_value - raw_new_value;
+#ifdef DCC_DECODER_DEBUG
+        debugLog_.add(new_value);
+#endif        
         bool cutout_just_finished = false;
         decoder_.process_data(new_value);
         if (decoder_.before_dcc_cutout())

src/freertos_drivers/common/SimpleLog.hxx

@@ -64,24 +64,22 @@ private:
 /// Actual class that keeps 8 log entries of one byte each.
 typedef SimpleLog<uint64_t> LogBuffer;
 
-
 /// Alternative for hundreds of entries.
-template<class T, int N> class LogRing {
+template <class T, int N> class LogRing
+{
 public:
-    void add(T data) {
-        data_[next_] = data;
-        last_ = data_ + next_;
-        if (next_) {
-            --next_;
-        } else {
-            next_ = N-1;
+    void add(T data)
+    {
+        data_[next_++] = data;
+        if (next_ >= N)
+        {
+            next_ = 0;
         }
     }
-    
+
 private:
     T data_[N];
-    unsigned next_{N};
-    T* last_{data_};
+    unsigned next_ {0};
 };
 
 #endif // _FREERTOS_DRIVERS_COMMON_SIMPLELOG_HXX_