X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;f=doc%2Fguides%2Fsample_app_ug%2Frxtx_callbacks.rst;h=0a69ec71abc36de4ab1d8496b893461e84f27fab;hb=2f827f5ea6e19f59386e82dc2dacb2ea353866f4;hp=1ca959c5579fc2e1d4c36b16fd28fe2e561f6078;hpb=6d13ea8e8e49ab957deae2bba5ecf4a4bfe747d1;p=dpdk.git

diff --git a/doc/guides/sample_app_ug/rxtx_callbacks.rst b/doc/guides/sample_app_ug/rxtx_callbacks.rst
index 1ca959c557..0a69ec71ab 100644
--- a/doc/guides/sample_app_ug/rxtx_callbacks.rst
+++ b/doc/guides/sample_app_ug/rxtx_callbacks.rst
@@ -13,6 +13,10 @@ In the sample application a user defined callback is applied to all received
 packets to add a timestamp. A separate callback is applied to all packets
 prior to transmission to calculate the elapsed time, in CPU cycles.
 
+If hardware timestamping is supported by the NIC, the sample application will
+also display the average latency since the packet was timestamped in hardware,
+on top of the latency since the packet was received and processed by the RX
+callback.
 
 Compiling the Application
 -------------------------
@@ -36,7 +40,10 @@ To run the example in a ``linux`` environment:
 
 .. code-block:: console
 
-    ./build/rxtx_callbacks -l 1 -n 4
+    ./build/rxtx_callbacks -l 1 -n 4 -- [-t]
+
+Use -t to enable hardware timestamping. If not supported by the NIC, an error
+will be displayed.
 
 Refer to *DPDK Getting Started Guide* for general information on running
 applications and the Environment Abstraction Layer (EAL) options.
@@ -110,8 +117,9 @@ comments:
             return retval;
 
         /* Enable RX in promiscuous mode for the Ethernet device. */
-        rte_eth_promiscuous_enable(port);
-
+        retval = rte_eth_promiscuous_enable(port);
+        if (retval != 0)
+            return retval;
 
         /* Add the callbacks for RX and TX.*/
         rte_eth_add_rx_callback(port, 0, add_timestamps, NULL);