Fix nasa#55, add timeout to SB receive

Apps should not pend forever on software bus receive, because
they should also periodically check CFE_ES_RunLoop even if no
commands were received.

fsw/src/sample_app.c

@@ -82,8 +82,14 @@ void SAMPLE_APP_Main(void)
         */
         CFE_ES_PerfLogExit(SAMPLE_APP_PERF_ID);
 
-        /* Pend on receipt of command packet */
-        status = CFE_SB_ReceiveBuffer(&SBBufPtr, SAMPLE_APP_Data.CommandPipe, CFE_SB_PEND_FOREVER);
+        /*
+         * Pend on receipt of command packet
+         *
+         * Note that apps should not wait forever here, to ensure
+         * that the status of CFE_ES_RunLoop() is also checked periodically,
+         * even if no software bus messages arrive.
+         */
+        status = CFE_SB_ReceiveBuffer(&SBBufPtr, SAMPLE_APP_Data.CommandPipe, SAMPLE_APP_SB_WAIT_PERIOD);
 
         /*
         ** Performance Log Entry Stamp
@@ -94,8 +100,9 @@ void SAMPLE_APP_Main(void)
         {
             SAMPLE_APP_ProcessCommandPacket(SBBufPtr);
         }
-        else
+        else if (status != CFE_SB_TIME_OUT)
         {
+            /* Timeout is normal if no activity, but anything else constitutes a real error */
             CFE_EVS_SendEvent(SAMPLE_APP_PIPE_ERR_EID, CFE_EVS_EventType_ERROR,
                               "SAMPLE APP: SB Pipe Read Error, App Will Exit");
 

fsw/src/sample_app.h

@@ -53,6 +53,17 @@
 #define SAMPLE_APP_TABLE_OUT_OF_RANGE_ERR_CODE -1
 
 #define SAMPLE_APP_TBL_ELEMENT_1_MAX 10
+
+/**
+ * \brief Amount of time to wait in CFE_SB_RecieveBuffer
+ *
+ * Applications need to wait for messages to arrive on the Software Bus,
+ * but this wait should be time limited to ensure that the app also
+ * periodically checks the status of CFE_ES_RunLoop(), in case an
+ * administrative command comes in.
+ */
+#define SAMPLE_APP_SB_WAIT_PERIOD 1000
+
 /************************************************************************
 ** Type Definitions
 *************************************************************************/