Had to give up on bitfields

src/uas/QGCUASFileManager.cc

@@ -80,7 +80,7 @@ QGCUASFileManager::QGCUASFileManager(QObject* parent, UASInterface* uas, uint8_t
     _systemIdServer = _mav->getUASID();
     
     // Make sure we don't have bad structure packing
-    Q_ASSERT(sizeof(RequestHeader) == 12);
+    Q_ASSERT(sizeof(RequestHeader) == 16);
 }
 
 /// @brief Calculates a 32 bit CRC for the specified request.
@@ -95,6 +95,9 @@ quint32 QGCUASFileManager::crc32(Request* request, unsigned state)
     // Always calculate CRC with 0 initial CRC value
     quint32 crcSave = request->hdr.crc32;
     request->hdr.crc32 = 0;
+    request->hdr.padding[0] = 0;
+    request->hdr.padding[1] = 0;
+    request->hdr.padding[2] = 0;
 
     for (size_t i=0; i < cbData; i++)
         state = crctab[(state ^ data[i]) & 0xff] ^ (state >> 8);

src/uas/QGCUASFileManager.h

@@ -75,16 +75,17 @@ public slots:
 
 protected:
     
-    /// @brief This is the fixed length portion of the protocol data. This structure is layed out such that it should not require
-    /// any special compiler packing to not consume extra space.
+    /// @brief This is the fixed length portion of the protocol data. Trying to pack structures across differing compilers is
+    /// questionable, so we pad the structure ourselves to 32 bit alignment which should get us what we want.
     struct RequestHeader
         {
-            uint16_t        seqNumber;  ///< sequence number for message
-            unsigned int    session:4;  ///< Session id for read and write commands
-            unsigned int    opcode:4;   ///< Command opcode
-            uint8_t         size;       ///< Size of data
-            uint32_t        crc32;      ///< CRC for entire Request structure, with crc32 set to 0
-            uint32_t        offset;     ///< Offsets for List and Read commands
+            uint16_t    seqNumber;  ///< sequence number for message
+            uint8_t     session;    ///< Session id for read and write commands
+            uint8_t     opcode;     ///< Command opcode
+            uint8_t     size;       ///< Size of data
+            uint8_t     padding[3];
+            uint32_t    crc32;      ///< CRC for entire Request structure, with crc32 and padding set to 0
+            uint32_t    offset;     ///< Offsets for List and Read commands
         };
 
     struct Request