Added a SICSLOWPAN_CONF_COMPRESSION_THRESHOLD that can be used to set a threshold under which header compression should not be used. Below this threshold, headers are not compressed but sent as full IPv6 packets. This is useful for RDC layers, such as ContikiMAC, which set a lower bound for packet size.

core/net/sicslowpan.c

@@ -165,6 +165,16 @@ void uip_log(char *msg);
 /** \brief Size of the 802.15.4 payload (127byte - 25 for MAC header) */
 #define MAC_MAX_PAYLOAD 102
 
+
+/** \brief Some MAC layers need a minimum payload, which is
+    configurable through the SICSLOWPAN_CONF_MIN_MAC_PAYLOAD
+    option. */
+#ifdef SICSLOWPAN_CONF_COMPRESSION_THRESHOLD
+#define COMPRESSION_THRESHOLD SICSLOWPAN_CONF_COMPRESSION_THRESHOLD
+#else
+#define COMPRESSION_THRESHOLD 0
+#endif
+
 /** \name General variables
  *  @{
  */
@@ -433,7 +443,7 @@ compress_hdr_hc06(rimeaddr_t *rime_destaddr)
   uint8_t tmp, iphc0, iphc1;
 #if DEBUG
   PRINTF("before compression: ");
-  for (tmp = 0; tmp < UIP_IP_BUF->len[1] + 40; tmp++) {
+  for(tmp = 0; tmp < UIP_IP_BUF->len[1] + 40; tmp++) {
     uint8_t data = ((uint8_t *) (UIP_IP_BUF))[tmp];
     PRINTF("%02x", data);
   }
@@ -1204,7 +1214,7 @@ uncompress_hdr_hc1(uint16_t ip_len)
 #endif /* SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_HC1 */
 
 
-#if SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_IPV6
+
 /*--------------------------------------------------------------------*/
 /** \name IPv6 dispatch "compression" function
  * @{                                                                 */
@@ -1232,9 +1242,6 @@ compress_hdr_ipv6(rimeaddr_t *rime_destaddr)
   return;
 }
 /** @} */
-#endif /* SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_IPV6 */
-
- 
 
 /*--------------------------------------------------------------------*/
 /** \name Input/output functions common to all compression schemes
@@ -1259,7 +1266,6 @@ packet_sent(void *ptr, int status, int transmissions)
 static void
 send_packet(rimeaddr_t *dest)
 {
-
   /* Set the link layer destination address for the packet as a
    * packetbuf attribute. The MAC layer can access the destination
    * address with the function packetbuf_addr(PACKETBUF_ADDR_RECEIVER).
@@ -1270,7 +1276,7 @@ send_packet(rimeaddr_t *dest)
 #if SICSLOWPAN_CONF_ACK_ALL
     packetbuf_set_attr(PACKETBUF_ATTR_RELIABLE, 1);
 #endif
-  
+
   /* Provide a callback function to receive the result of
      a packet transmission. */
   NETSTACK_MAC.send(&packet_sent, NULL);
@@ -1279,7 +1285,7 @@ send_packet(rimeaddr_t *dest)
      watchdog know that we are still alive. */
   watchdog_periodic();
 }
-
+/*--------------------------------------------------------------------*/
 /** \brief Take an IP packet and format it to be sent on an 802.15.4
  *  network using 6lowpan.
  *  \param localdest The MAC address of the destination
@@ -1294,7 +1300,6 @@ output(uip_lladdr_t *localdest)
 {
   /* The MAC address of the destination of the packet */
   rimeaddr_t dest;
-  
 
   /* init */
   uncomp_hdr_len = 0;
@@ -1334,19 +1339,23 @@ output(uip_lladdr_t *localdest)
   }
   
   PRINTFO("sicslowpan output: sending packet len %d\n", uip_len);
-  
+
-  /* Try to compress the headers */
+  if(uip_len >= COMPRESSION_THRESHOLD) {
+    /* Try to compress the headers */
 #if SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_HC1
-  compress_hdr_hc1(&dest);
+    compress_hdr_hc1(&dest);
 #endif /* SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_HC1 */
 #if SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_IPV6
-  compress_hdr_ipv6(&dest);
+    compress_hdr_ipv6(&dest);
 #endif /* SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_IPV6 */
 #if SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_HC06
-  compress_hdr_hc06(&dest);
+    compress_hdr_hc06(&dest);
 #endif /* SICSLOWPAN_COMPRESSION == SICSLOWPAN_COMPRESSION_HC06 */
+  } else {
+    compress_hdr_ipv6(&dest);
+  }
   PRINTFO("sicslowpan output: header of len %d\n", rime_hdr_len);
-  
+
   if(uip_len - uncomp_hdr_len > MAC_MAX_PAYLOAD - rime_hdr_len) {
 #if SICSLOWPAN_CONF_FRAG
     struct queuebuf *q;
@@ -1358,7 +1367,6 @@ output(uip_lladdr_t *localdest)
      * The following fragments contain only the fragn dispatch.
      */
 
-
     PRINTFO("Fragmentation sending packet len %d\n", uip_len);
     
     /* Create 1st Fragment */