Set ipBUFFER_PADDING to 14 bytes by default on 64 bit targets v2 (Fre…

…eRTOS#1061)

* Set ipBUFFER_PADDING to 14 bytes by default on 64 bit targets v2

* Added U suffix to some literal values like 0xFFFFFFFFU

* Corrected the offset/size table in the comments

* Changes ipBUFFER_PADDING checks after review Monika and Tony

---------

Co-authored-by: Tony Josi <tonyjosi@amazon.com>

source/FreeRTOS_IP_Utils.c

@@ -983,18 +983,28 @@ void vPreCheckConfigs( void )
 
     #if ( configASSERT_DEFINED == 1 )
     {
-        volatile size_t uxSize = sizeof( uintptr_t );
-
-        if( uxSize == 8U )
-        {
-            /* This is a 64-bit platform, make sure there is enough space in
-             * pucEthernetBuffer to store a pointer and also make sure that the value of
-             * ipconfigBUFFER_PADDING is such that (ipconfigBUFFER_PADDING + ipSIZE_OF_ETH_HEADER) is a
-             * 32 bit (4 byte) aligned value, so that when incrementing the ethernet buffer with
-             * (ipconfigBUFFER_PADDING + ipSIZE_OF_ETH_HEADER) bytes it lands in a 32 bit aligned address
-             * which lets us efficiently access 32 bit values later in the packet. */
-            configASSERT( ( ipconfigBUFFER_PADDING >= 14 ) && ( ( ( ( ipconfigBUFFER_PADDING ) + ( ipSIZE_OF_ETH_HEADER ) ) % 4 ) == 0 ) );
-        }
+        size_t uxSize;
+
+        /* Check if ipBUFFER_PADDING has a minimum size, depending on the platform.
+         * See FreeRTOS_IP.h for more details. */
+        #if ( UINTPTR_MAX > 0xFFFFFFFFU )
+
+            /*
+             * This is a 64-bit platform, make sure there is enough space in
+             * pucEthernetBuffer to store a pointer.
+             */
+            configASSERT( ipBUFFER_PADDING >= 14U );
+        #else
+            /* This is a 32-bit platform. */
+            configASSERT( ipBUFFER_PADDING >= 10U );
+        #endif /* UINTPTR_MAX > 0xFFFFFFFFU */
+
+        /*
+         * The size of the Ethernet header (14) plus ipBUFFER_PADDING should be a
+         * multiple of 32 bits, in order to get aligned access to all uint32_t
+         * fields in the protocol headers.
+         */
+        configASSERT( ( ( ( ipSIZE_OF_ETH_HEADER ) + ( ipBUFFER_PADDING ) ) % 4U ) == 0U );
 
         /* LCOV_EXCL_BR_START */
         uxSize = ipconfigNETWORK_MTU;

source/include/FreeRTOS_IP.h

@@ -97,22 +97,30 @@ extern uint32_t ulApplicationGetNextSequenceNumber( uint32_t ulSourceAddress,
  * pointer back to the network buffer.  Should be a multiple of 8 to ensure 8 byte
  * alignment is maintained on architectures that require it.
  *
- * In order to get a 32-bit alignment of network packets, an offset of 2 bytes
- * would be desirable, as defined by ipconfigPACKET_FILLER_SIZE.  So the malloc'd
+ * In order to get a 32-bit or 64-bit alignment of network packets, an offset of 2 bytes
+ * is ideal as defined by ipconfigPACKET_FILLER_SIZE. So the malloc'd
  * buffer will have the following contents:
- *  uint32_t pointer;   // word-aligned
- *  uchar_8 filler[6];
- *  << ETH-header >>    // half-word-aligned
- *  uchar_8 dest[6];    // start of pucEthernetBuffer
- *  uchar_8 dest[6];
- *  uchar16_t type;
- *  << IP-header >>     // word-aligned
+ *
+ * +---------+-----------+---------+
+ * | Offset  | Alignment | Length  |
+ * | 32 | 64 | 32  | 64  | 32 | 64 |
+ * |----|----|-----|-----|----|----|
+ * | 0  | 0  | 4   | 8   | 4  | 8  | uchar_8 * pointer;     // Points to the 'NetworkBufferDescriptor_t'.
+ * | 4  | 8  | 4   | 8   | 6  | 6  | uchar_8   filler[6];   // To give the +2 byte offset.
+ * |-------------------------------|
+ * | 10 | 14 | 4+2 | 8+2 | 6  | 6  | uchar_8   dest_mac[6]; // Destination address.
+ * | 16 | 20 | 4   | 8   | 6  | 6  | uchar_8   src_mac[6];  // Source address.
+ * | 22 | 26 | 4+2 | 4+2 | 2  | 2  | uchar16_t ethertype;
+ * | 24 | 28 | 4   | 4   | ~  | ~  | << IP-header >>        // word-aligned, either 4 or 8 bytes.
  *  uint8_t ucVersionHeaderLength;
  *  etc
  */
 
-#if ( ipconfigBUFFER_PADDING != 0 )
+/* Use setting from FreeRTOS if defined and non-zero */
+#if defined( ipconfigBUFFER_PADDING ) && ( ipconfigBUFFER_PADDING != 0 )
     #define ipBUFFER_PADDING    ipconfigBUFFER_PADDING
+#elif ( UINTPTR_MAX > 0xFFFFFFFF )
+    #define ipBUFFER_PADDING    ( 12U + ipconfigPACKET_FILLER_SIZE )
 #else
     #define ipBUFFER_PADDING    ( 8U + ipconfigPACKET_FILLER_SIZE )
 #endif