+**DPDK Configuration Parameter**
+
+ * **RTE_LIBRTE_ARK_MIN_TX_PKTLEN** (default 0): Sets the minimum
+ packet length for tx packets to the FPGA. Packets less than this
+ length are padded to meet the requirement. This allows padding to
+ be offloaded or remain in host software.
+
+
+Dynamic PMD Extension
+---------------------
+
+Dynamic PMD extensions allow users to customize net/ark functionality
+using their own code. Arkville RTL and this PMD support high-throughput data
+movement, and these extensions allow PMD support for users' FPGA
+features.
+Dynamic PMD extensions operate by having users supply a shared object
+file which is loaded by Arkville PMD during initialization. The
+object file contains extension (or hook) functions that are registered
+and then called during PMD operations.
+
+The allowable set of extension functions are defined and documented in
+``ark_ext.h``, only the initialization function,
+``rte_pmd_ark_dev_init()``, is required; all others are optional. The
+following sections give a small extension example along with
+instructions for compiling and using the extension.
+
+
+Extension Example
+^^^^^^^^^^^^^^^^^
+
+The following example shows an extension which populates mbuf fields
+during RX from user meta data coming from FPGA hardware.
+
+.. code-block:: c
+
+ #include <ark_ext.h>
+ #include <rte_mbuf.h>
+ #include <rte_ethdev.h>
+ #include <rte_malloc.h>
+
+ /* Global structure passed to extension/hook functions */
+ struct ark_user_extension {
+ int timestamp_dynfield_offset;
+ };
+
+ /* RX tuser field based on user's hardware */
+ struct user_rx_meta {
+ uint64_t timestamp;
+ uint32_t rss;
+ } __rte_packed;
+
+ /* Create ark_user_extension object for use in other hook functions */
+ void *rte_pmd_ark_dev_init(struct rte_eth_dev * dev,
+ void * abar, int port_id )
+ {
+ RTE_SET_USED(dev);
+ RTE_SET_USED(abar);
+ fprintf(stderr, "Called Arkville user extension for port %u\n",
+ port_id);
+
+ struct ark_user_extension *xdata = rte_zmalloc("macExtS",
+ sizeof(struct ark_user_extension), 64);
+ if (!xdata)
+ return NULL;
+
+ /* register dynfield for rx timestamp */
+ rte_mbuf_dyn_rx_timestamp_register(&xdata->timestamp_dynfield_offset,
+ NULL);
+
+ fprintf(stderr, "timestamp fields offset in extension is %d\n",
+ xdata->timestamp_dynfield_offset);
+ return xdata;
+ }
+
+ /* uninitialization */
+ void rte_pmd_ark_dev_uninit(struct rte_eth_dev * dev, void *user_data)
+ {
+ rte_free(user_data);
+ }
+
+ /* Hook function -- called for each RX packet
+ * Extract RX timestamp and RSS from meta and place in mbuf
+ */
+ void rte_pmd_ark_rx_user_meta_hook(struct rte_mbuf *mbuf,
+ const uint32_t *meta,
+ void *user_data)
+ {
+ struct ark_user_extension *xdata = user_data;
+ struct user_rx_meta *user_rx = (struct user_rx_meta*)meta;
+ *RTE_MBUF_DYNFIELD(mbuf, xdata->timestamp_dynfield_offset, uint64_t*) =
+ user_rx->timestamp;
+ mbuf->hash.rss = user_rx->rss;
+ }
+
+
+Compiling Extension
+^^^^^^^^^^^^^^^^^^^
+
+It is recommended to the compile the extension code with
+``-Wmissing-prototypes`` flag to insure correct function types. Typical
+DPDK options will also be needed.
+
+
+An example command line is give below