Add a nice error message to ethercatctl in case of missing config.

script/ethercatctl.in

@@ -102,6 +102,14 @@ start)
         MASTER_INDEX=$((${MASTER_INDEX} + 1))
     done
 
+    if [ -z "${DEVICES}" ]; then
+        echo "ERROR: No network cards for EtherCAT specified."
+        echo -n "Please edit ${ETHERCAT_CONFIG} with root permissions"
+        echo -n " and set MASTER0_DEVICE variable to either a "
+        echo "network interface name (like eth0) or to a MAC address."
+        exit 1
+    fi
+
     # load master module
     if ! ${MODPROBE} ${MODPROBE_FLAGS} ec_master \
             main_devices="${DEVICES}" backup_devices="${BACKUPS}"; then