void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
  if (huart->Instance == huart1.Instance)
  {
      // Don't overwrite existing data.
      if (((_RxHead + 1) % BUFFER_SIZE) != _RxTail)
      {
          // Check for sysex.
          if (_SysexReceived == 0)
          {
              if (_RxByte == 0xF0)
              {
                  _RxBuffer[_RxHead] = _RxByte;
                  _RxHead = (_RxHead + 1) % BUFFER_SIZE;
                  _SysexReceived = 1;
              }

              // No sysex, skip active sensing/timing.
              else if ((_RxByte != 0xF8) && (_RxByte != 0xFE))
              {
                  // Add byte.
                  _RxBuffer[_RxHead] = _RxByte;
                  _RxHead = (_RxHead + 1) % BUFFER_SIZE;
              }
          }
          else if (_SysexReceived < MAX_SYSEX_LENGTH)
          {
              // Sysex: add byte.
              _RxBuffer[_RxHead] = _RxByte;
              _RxHead = (_RxHead + 1) % BUFFER_SIZE;
              _SysexReceived = (_RxByte == 0xF7) ? 0 : _SysexReceived + 1;
          }
          else // SysexReceived >= (or ==) MAX_SYSEX_LENGTH
          {
              // Too long message, only write last 0x7F.
              if (_RxByte == 0xF7)
              {
                  _RxBuffer[_RxHead] = _RxByte;
                  _RxHead = (_RxHead + 1) % BUFFER_SIZE;
                  _SysexReceived = 0;
              }
          }

#ifdef __BUFFER_DEBUG
          __ReceivedBufferData[__ReceivedIndex] = _RxByte;
          __ReceivedBufferHead[__ReceivedIndex] = _RxHead;
          __ReceivedBufferTail[__ReceivedIndex] = _RxTail;
          __ReceivedBufferSysex[__ReceivedIndex] = _SysexReceived;
          __ReceivedIndex++;
          if (__ReceivedIndex == __RECEIVED_BUFFER_SIZE)
          {
              __ReceivedIndex = 0;
              __ReceivedRounds++;
          }
#endif
      }
      else
      {
          _Error_Handler(__FILE__, __LINE__);
      }
   }
}