gnrc_ipv6_nib: sync RTT64 with RA timestamp

sys/net/gnrc/Makefile.dep

@@ -381,6 +381,10 @@ ifneq (,$(filter gnrc_ipv6_nib_router,$(USEMODULE)))
   USEMODULE += gnrc_ipv6_nib
 endif
 
+ifneq (,$(filter gnrc_ipv6_nib_timestamp,$(USEMODULE)))
+  USEMODULE += rtt64
+endif
+
 ifneq (,$(filter gnrc_ipv6_nib,$(USEMODULE)))
   DEFAULT_MODULE += auto_init_gnrc_ipv6_nib
   USEMODULE += evtimer

sys/net/gnrc/network_layer/ipv6/nib/nib.c

@@ -37,6 +37,10 @@
 #include "net/dhcpv6/client.h"
 #endif
 
+#if IS_USED(MODULE_RTT64)
+#include "rtt64.h"
+#endif
+
 #include "_nib-internal.h"
 #include "_nib-arsm.h"
 #include "_nib-router.h"
@@ -1672,11 +1676,33 @@ static void _handle_timestamp(const ndp_opt_timestamp_t *tsmp)
         return;
     }
 
-    uint64_t seconds = byteorder_ntohll(tsmp->timestamp) >> 16;
-    uint16_t ms = (1000 * (seconds & 0xFFFF)) >> 16;
-
+    uint64_t now = byteorder_ntohll(tsmp->timestamp);
     DEBUG("nib: received Timestamp option:\n");
-    DEBUG("     - Seconds: %u\n", (unsigned)seconds);
-    DEBUG("     - Milliseconds: %u\n", ms);
+    DEBUG("     - Seconds: %u\n", (unsigned)(now >> 16));
+    DEBUG("     - Milliseconds: %u\n", (unsigned)(1000 * (now & 0xFFFF)) >> 16);
+#if IS_USED(MODULE_RTT64)
+    static uint16_t diff;
+    uint64_t local = rtt64_get_counter();
+    now += diff;
+
+    rtt64_set_counter(now);
+
+    DEBUG("     - remote: %u ticks\n", (unsigned)now);
+    DEBUG("     - local: %u ticks\n", (unsigned)local);
+    DEBUG("     - diff: %u ticks\n", diff);
+
+    /* try to account for transmission time */
+    /* only do diff accounting if diff is less than 1s */
+    if ((now < local) && (local - now < 0xFFFF)) {
+        /* now is already now + diff */
+        diff = (local - now) / 2;
+        DEBUG("     - new diff: %u ticks\n", diff);
+    } else if ((now > local) && (now - local < 0xFFFF)) {
+        diff -= _min(diff, now - local);
+        DEBUG("     - new diff: %u ticks (%u ticks too fast)\n", diff, (unsigned)(now - local));
+    } else {
+        diff = 0;
+    }
+#endif
 }
 /** @} */

sys/net/gnrc/network_layer/ndp/gnrc_ndp.c

@@ -25,6 +25,7 @@
 #include "net/gnrc/sixlowpan/nd.h"
 #endif
 #include "net/ndp.h"
+#include "rtt64.h"
 
 #include "net/gnrc/ndp.h"
 
@@ -529,6 +530,14 @@ void gnrc_ndp_rtr_adv_send(gnrc_netif_t *netif, const ipv6_addr_t *src,
             }
             pkt = hdr;
         }
+        if (IS_USED(MODULE_GNRC_IPV6_NIB_TIMESTAMP) && IS_USED(MODULE_RTT64)) {
+            uint64_t now = rtt64_get_counter();
+            if ((hdr = gnrc_ndp_opt_timestamp_build(now, pkt)) == NULL) {
+                DEBUG("ndp rtr: no space left in packet buffer\n");
+                break;
+            }
+            pkt = hdr;
+        }
         if (src == NULL) {
             /* get address from source selection algorithm.
              * Only link local addresses may be used (RFC 4861 section 4.1) */