diff -r eb5d60aeb9d0 -r 703c5503aa97 src/cpu/testers/traffic_gen/traffic_gen.cc
--- a/src/cpu/testers/traffic_gen/traffic_gen.cc	Tue Aug 20 11:55:31 2013 -0700
+++ b/src/cpu/testers/traffic_gen/traffic_gen.cc	Thu Aug 22 13:12:53 2013 -0700
@@ -119,6 +119,11 @@
 unsigned int
 TrafficGen::drain(DrainManager *dm)
 {
+    if (!updateEvent.scheduled()) {
+        // no event has been scheduled yet (e.g. switched from atomic mode)
+        return 0;
+    }
+
     if (retryPkt == NULL) {
         // shut things down
         nextPacketTick = MaxTick;