Fix #38: Add union for proper TLM buffer alignment

Put the HkTlm buffer into a union to ensure it is aligned
appropriately for conversion to a CFE_SB_Msg_t type.

Author: jphickey

fsw/src/sample_app.c

@@ -174,7 +174,7 @@ int32 SAMPLE_AppInit( void )
     /*
     ** Initialize housekeeping packet (clear user data area).
     */
-    CFE_SB_InitMsg(&SAMPLE_AppData.HkBuf,
+    CFE_SB_InitMsg(&SAMPLE_AppData.HkBuf.MsgHdr,
                    SAMPLE_APP_HK_TLM_MID,
                    sizeof(SAMPLE_AppData.HkBuf),
                    true);
@@ -356,14 +356,14 @@ int32 SAMPLE_ReportHousekeeping( const CCSDS_CommandPacket_t *Msg )
     /*
     ** Get command execution counters...
     */
-    SAMPLE_AppData.HkBuf.Payload.CommandErrorCounter = SAMPLE_AppData.ErrCounter;
-    SAMPLE_AppData.HkBuf.Payload.CommandCounter = SAMPLE_AppData.CmdCounter;
+    SAMPLE_AppData.HkBuf.HkTlm.Payload.CommandErrorCounter = SAMPLE_AppData.ErrCounter;
+    SAMPLE_AppData.HkBuf.HkTlm.Payload.CommandCounter = SAMPLE_AppData.CmdCounter;
 
     /*
     ** Send housekeeping telemetry packet...
     */
-    CFE_SB_TimeStampMsg(&SAMPLE_AppData.HkBuf);
-    CFE_SB_SendMsg(&SAMPLE_AppData.HkBuf);
+    CFE_SB_TimeStampMsg(&SAMPLE_AppData.HkBuf.MsgHdr);
+    CFE_SB_SendMsg(&SAMPLE_AppData.HkBuf.MsgHdr);
 
     /*
     ** Manage any pending table loads, validations, etc.

fsw/src/sample_app.h

@@ -56,6 +56,17 @@
 /************************************************************************
 ** Type Definitions
 *************************************************************************/
+
+/*
+ * Buffer to hold telemetry data prior to sending
+ * Defined as a union to ensure proper alignment for a CFE_SB_Msg_t type
+ */
+typedef union
+{
+    CFE_SB_Msg_t        MsgHdr;
+    SAMPLE_HkTlm_t      HkTlm;
+} SAMPLE_HkBuffer_t;
+
 /*
 ** Global Data
 */
@@ -70,7 +81,7 @@ typedef struct
     /*
     ** Housekeeping telemetry packet...
     */
-    SAMPLE_HkTlm_t        HkBuf;
+    SAMPLE_HkBuffer_t     HkBuf;
 
     /*
     ** Run Status variable used in the main processing loop