Improve comments and assertions in stream buffer (#277)

* Improve comments and assertions in stream buffer

* Add back null check instead of assert

* Adding config assert back

stream_buffer.c

@@ -49,7 +49,7 @@
 #undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE /*lint !e961 !e750 !e9021. */
 
 /* If the user has not provided application specific Rx notification macros,
- * or #defined the notification macros away, them provide default implementations
+ * or #defined the notification macros away, then provide default implementations
  * that uses task notifications. */
 /*lint -save -e9026 Function like macros allowed and needed here so they can be overridden. */
 #ifndef sbRECEIVE_COMPLETED
@@ -268,7 +268,6 @@ static void prvInitialiseNewStreamBuffer( StreamBuffer_t * const pxStreamBuffer,
             pucAllocatedMemory = NULL;
         }
 
-
         if( pucAllocatedMemory != NULL )
         {
             prvInitialiseNewStreamBuffer( ( StreamBuffer_t * ) pucAllocatedMemory,       /* Structure at the start of the allocated memory. */ /*lint !e9087 Safe cast as allocated memory is aligned. */ /*lint !e826 Area is not too small and alignment is guaranteed provided malloc() behaves as expected and returns aligned buffer. */
@@ -466,7 +465,7 @@ BaseType_t xStreamBufferSetTriggerLevel( StreamBufferHandle_t xStreamBuffer,
 
     /* The trigger level is the number of bytes that must be in the stream
      * buffer before a task that is waiting for data is unblocked. */
-    if( xTriggerLevel <= pxStreamBuffer->xLength )
+    if( xTriggerLevel < pxStreamBuffer->xLength )
     {
         pxStreamBuffer->xTriggerLevelBytes = xTriggerLevel;
         xReturn = pdPASS;
@@ -525,14 +524,15 @@ size_t xStreamBufferSend( StreamBufferHandle_t xStreamBuffer,
     size_t xReturn, xSpace = 0;
     size_t xRequiredSpace = xDataLengthBytes;
     TimeOut_t xTimeOut;
-
+    size_t xMaxReportedSpace = 0;
-    /* The maximum amount of space a stream buffer will ever report is its length
-     * minus 1. */
-    const size_t xMaxReportedSpace = pxStreamBuffer->xLength - ( size_t ) 1;
 
     configASSERT( pvTxData );
     configASSERT( pxStreamBuffer );
 
+    /* The maximum amount of space a stream buffer will ever report is its length
+     * minus 1. */
+    xMaxReportedSpace = pxStreamBuffer->xLength - ( size_t ) 1;
+
     /* This send function is used to write to both message buffers and stream
      * buffers.  If this is a message buffer then the space needed must be
      * increased by the amount of bytes needed to store the length of the