diff -r f859d567f94e -r 42b62867574d master/fsm_slave_config.c
--- a/master/fsm_slave_config.c	Fri Jan 22 10:11:58 2016 +0100
+++ b/master/fsm_slave_config.c	Fri Jan 22 13:09:43 2016 +0100
@@ -1399,8 +1399,12 @@
             EC_SLAVE_WARN(slave, "Slave did not sync after %lu ms.\n",
                     diff_ms);
         } else {
-            EC_SLAVE_DBG(slave, 1, "Sync after %4lu ms: %10u ns\n",
-                    diff_ms, abs_sync_diff);
+            static unsigned long last_diff_ms = 0;
+            if ((diff_ms < last_diff_ms) || (diff_ms >= (last_diff_ms + 100))) {
+                last_diff_ms = diff_ms;
+                EC_SLAVE_DBG(slave, 1, "Sync after %4lu ms: %10u ns\n",
+                        diff_ms, abs_sync_diff);
+            }
 
             // check synchrony again
             ec_datagram_fprd(datagram, slave->station_address, 0x092c, 4);