Merge branch 'master' of ettus.sourcerepo.com:ettus/uhdpriv into usrp_e

Conflicts:
	host/utils/CMakeLists.txt

5 files changed, 464 insertions, 76 deletions

diff --git a/host/lib/transport/CMakeLists.txt b/host/lib/transport/CMakeLists.txt
index a36f0fc03..ed8c35225 100644
--- a/host/lib/transport/CMakeLists.txt
+++ b/host/lib/transport/CMakeLists.txt
@@ -49,4 +49,5 @@ LIBUHD_APPEND_SOURCES(
     ${CMAKE_SOURCE_DIR}/lib/transport/if_addrs.cpp
     ${CMAKE_SOURCE_DIR}/lib/transport/udp_simple.cpp
     ${CMAKE_SOURCE_DIR}/lib/transport/udp_zero_copy_asio.cpp
+    ${CMAKE_SOURCE_DIR}/lib/transport/vrt_packet_handler.hpp
 )
diff --git a/host/lib/transport/convert_types.cpp b/host/lib/transport/convert_types.cpp
index 8c3d6b17a..43503025a 100644
--- a/host/lib/transport/convert_types.cpp
+++ b/host/lib/transport/convert_types.cpp
@@ -15,6 +15,7 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 //
 
+#include <uhd/config.hpp>
 #include <uhd/transport/convert_types.hpp>
 #include <uhd/utils/assert.hpp>
 #include <boost/asio.hpp> //endianness conversion
@@ -49,7 +50,7 @@ static const bool is_big_endian = true;
 static const bool is_big_endian = false;
 #endif
 
-static inline void host_floats_to_usrp2_items(
+static UHD_INLINE void host_floats_to_usrp2_items(
     boost::uint32_t *usrp2_items,
     const fc32_t *host_floats,
     size_t num_samps
@@ -62,7 +63,7 @@ static inline void host_floats_to_usrp2_items(
     unrolled_loop(host_floats_to_usrp2_items_i, num_samps);
 }
 
-static inline void usrp2_items_to_host_floats(
+static UHD_INLINE void usrp2_items_to_host_floats(
     fc32_t *host_floats,
     const boost::uint32_t *usrp2_items,
     size_t num_samps
@@ -76,7 +77,7 @@ static inline void usrp2_items_to_host_floats(
     unrolled_loop(usrp2_items_to_host_floats_i, num_samps);
 }
 
-static inline void host_items_to_usrp2_items(
+static UHD_INLINE void host_items_to_usrp2_items(
     boost::uint32_t *usrp2_items,
     const boost::uint32_t *host_items,
     size_t num_samps
@@ -90,7 +91,7 @@ static inline void host_items_to_usrp2_items(
     }
 }
 
-static inline void usrp2_items_to_host_items(
+static UHD_INLINE void usrp2_items_to_host_items(
     boost::uint32_t *host_items,
     const boost::uint32_t *usrp2_items,
     size_t num_samps
@@ -115,10 +116,13 @@ void transport::convert_io_type_to_otw_type(
     switch(io_type.tid){
     case io_type_t::COMPLEX_FLOAT32:
         host_floats_to_usrp2_items((boost::uint32_t *)otw_buff, (const fc32_t*)io_buff, num_samps);
-        break;
+        return;
     case io_type_t::COMPLEX_INT16:
         host_items_to_usrp2_items((boost::uint32_t *)otw_buff, (const boost::uint32_t*)io_buff, num_samps);
-        break;
+        return;
+     case io_type_t::CUSTOM_TYPE:
+        std::memcpy(otw_buff, io_buff, num_samps*io_type.size);
+        return;
     default:
         throw std::runtime_error(str(boost::format("convert_types: cannot handle type \"%c\"") % io_type.tid));
     }
@@ -135,10 +139,13 @@ void transport::convert_otw_type_to_io_type(
     switch(io_type.tid){
     case io_type_t::COMPLEX_FLOAT32:
         usrp2_items_to_host_floats((fc32_t*)io_buff, (const boost::uint32_t *)otw_buff, num_samps);
-        break;
+        return;
     case io_type_t::COMPLEX_INT16:
         usrp2_items_to_host_items((boost::uint32_t*)io_buff, (const boost::uint32_t *)otw_buff, num_samps);
-        break;
+        return;
+    case io_type_t::CUSTOM_TYPE:
+        std::memcpy(io_buff, otw_buff, num_samps*io_type.size);
+        return;
     default:
         throw std::runtime_error(str(boost::format("convert_types: cannot handle type \"%c\"") % io_type.tid));
     }
diff --git a/host/lib/transport/gen_vrt.py b/host/lib/transport/gen_vrt.py
index 9a57c83c3..c34ffb198 100755
--- a/host/lib/transport/gen_vrt.py
+++ b/host/lib/transport/gen_vrt.py
@@ -57,7 +57,7 @@ void vrt::pack(
     size_t packet_count,           //input
     double tick_rate               //input
 ){
-    boost::uint32_t vrt_hdr_flags;
+    boost::uint32_t vrt_hdr_flags = 0;
 
     boost::uint8_t pred = 0;
     if (metadata.has_stream_id) pred |= $hex($sid_p);
diff --git a/host/lib/transport/udp_zero_copy_asio.cpp b/host/lib/transport/udp_zero_copy_asio.cpp
index ee44803f4..f8a222475 100644
--- a/host/lib/transport/udp_zero_copy_asio.cpp
+++ b/host/lib/transport/udp_zero_copy_asio.cpp
@@ -16,75 +16,69 @@
 //
 
 #include <uhd/transport/udp_zero_copy.hpp>
+#include <uhd/utils/assert.hpp>
 #include <boost/cstdint.hpp>
 #include <boost/asio.hpp>
-#include <boost/thread.hpp>
 #include <boost/format.hpp>
 #include <iostream>
 
 using namespace uhd::transport;
 
 /***********************************************************************
+ * Constants
+ **********************************************************************/
+static const size_t MIN_SOCK_BUFF_SIZE = size_t(100e3);
+static const size_t MAX_DGRAM_SIZE = 2048; //assume max size on send and recv
+static const double RECV_TIMEOUT = 0.1; // 100 ms
+
+/***********************************************************************
  * Managed receive buffer implementation for udp zero-copy asio:
- *   Frees the memory held by the const buffer on done.
  **********************************************************************/
 class managed_recv_buffer_impl : public managed_recv_buffer{
 public:
     managed_recv_buffer_impl(const boost::asio::const_buffer &buff) : _buff(buff){
-        _done = false;
+        /* NOP */
     }
 
     ~managed_recv_buffer_impl(void){
-        if (not _done) this->done();
-    }
-
-    void done(void){
-        _done = true;
-        delete [] boost::asio::buffer_cast<const boost::uint32_t *>(_buff);
+        delete [] this->cast<const boost::uint8_t *>();
     }
 
 private:
-    const boost::asio::const_buffer &get(void){
+    const boost::asio::const_buffer &get(void) const{
         return _buff;
     }
 
     const boost::asio::const_buffer _buff;
-    bool _done;
 };
 
 /***********************************************************************
  * Managed send buffer implementation for udp zero-copy asio:
- *   Sends and frees the memory held by the mutable buffer on done.
  **********************************************************************/
 class managed_send_buffer_impl : public managed_send_buffer{
 public:
     managed_send_buffer_impl(
         const boost::asio::mutable_buffer &buff,
         boost::asio::ip::udp::socket *socket
-    ) : _buff(buff){
-        _done = false;
-        _socket = socket;
+    ) : _buff(buff), _socket(socket){
+        /* NOP */
     }
 
     ~managed_send_buffer_impl(void){
-        if (not _done) this->done(0);
+        /* NOP */
     }
 
-    void done(size_t num_bytes){
-        _done = true;
-        boost::uint32_t *mem = boost::asio::buffer_cast<boost::uint32_t *>(_buff);
-        _socket->send(boost::asio::buffer(mem, num_bytes));
-        delete [] mem;
+    void commit(size_t num_bytes){
+        _socket->send(boost::asio::buffer(_buff, num_bytes));
     }
 
 private:
-    const boost::asio::mutable_buffer &get(void){
+    const boost::asio::mutable_buffer &get(void) const{
         return _buff;
     }
 
     const boost::asio::mutable_buffer _buff;
     boost::asio::ip::udp::socket      *_socket;
-    bool _done;
 };
 
 /***********************************************************************
@@ -96,6 +90,8 @@ private:
  **********************************************************************/
 class udp_zero_copy_impl : public udp_zero_copy{
 public:
+    typedef boost::shared_ptr<udp_zero_copy_impl> sptr;
+
     //structors
     udp_zero_copy_impl(const std::string &addr, const std::string &port);
     ~udp_zero_copy_impl(void);
@@ -104,23 +100,27 @@ public:
     managed_recv_buffer::sptr get_recv_buff(void);
     managed_send_buffer::sptr get_send_buff(void);
 
-    //resize
-    size_t resize_recv_buff(size_t num_bytes){
-        boost::asio::socket_base::receive_buffer_size option(num_bytes);
-        _socket->set_option(option);
+    //manage buffer
+    template <typename Opt> size_t get_buff_size(void){
+        Opt option;
         _socket->get_option(option);
         return option.value();
     }
-    size_t resize_send_buff(size_t num_bytes){
-        boost::asio::socket_base::send_buffer_size option(num_bytes);
+
+    template <typename Opt> size_t resize_buff(size_t num_bytes){
+        Opt option(num_bytes);
         _socket->set_option(option);
-        _socket->get_option(option);
-        return option.value();
+        return get_buff_size<Opt>();
     }
 
 private:
     boost::asio::ip::udp::socket   *_socket;
     boost::asio::io_service        _io_service;
+
+    //send and recv buffer memory (allocated once)
+    boost::uint8_t _send_mem[MIN_SOCK_BUFF_SIZE];
+
+    managed_send_buffer::sptr _send_buff;
 };
 
 udp_zero_copy_impl::udp_zero_copy_impl(const std::string &addr, const std::string &port){
@@ -131,10 +131,25 @@ udp_zero_copy_impl::udp_zero_copy_impl(const std::string &addr, const std::strin
     boost::asio::ip::udp::resolver::query query(boost::asio::ip::udp::v4(), addr, port);
     boost::asio::ip::udp::endpoint receiver_endpoint = *resolver.resolve(query);
 
-    // Create, open, and connect the socket
+    // create, open, and connect the socket
     _socket = new boost::asio::ip::udp::socket(_io_service);
     _socket->open(boost::asio::ip::udp::v4());
     _socket->connect(receiver_endpoint);
+
+    // create the managed send buff (just once)
+    _send_buff = managed_send_buffer::sptr(new managed_send_buffer_impl(
+        boost::asio::buffer(_send_mem, MIN_SOCK_BUFF_SIZE), _socket
+    ));
+
+    // set recv timeout
+    timeval tv;
+    tv.tv_sec = 0;
+    tv.tv_usec = size_t(RECV_TIMEOUT*1e6);
+    UHD_ASSERT_THROW(setsockopt(
+        _socket->native(),
+        SOL_SOCKET, SO_RCVTIMEO,
+        (const char *)&tv, sizeof(timeval)
+    ) == 0);
 }
 
 udp_zero_copy_impl::~udp_zero_copy_impl(void){
@@ -142,61 +157,56 @@ udp_zero_copy_impl::~udp_zero_copy_impl(void){
 }
 
 managed_recv_buffer::sptr udp_zero_copy_impl::get_recv_buff(void){
-    //implement timeout through polling and sleeping
-    size_t available = 0;
-    boost::asio::deadline_timer timer(_socket->get_io_service());
-    timer.expires_from_now(boost::posix_time::milliseconds(100));
-    while (not ((available = _socket->available()) or timer.expires_from_now().is_negative())){
-        boost::this_thread::sleep(boost::posix_time::milliseconds(1));
-    }
+    //allocate memory
+    boost::uint8_t *recv_mem = new boost::uint8_t[MAX_DGRAM_SIZE];
 
-    //receive only if data is available
-    boost::uint32_t *buff_mem = new boost::uint32_t[available/sizeof(boost::uint32_t)];
-    if (available){
-        available = _socket->receive(boost::asio::buffer(buff_mem, available));
-    }
+    //call recv() with timeout option
+    size_t num_bytes = _socket->receive(boost::asio::buffer(recv_mem, MIN_SOCK_BUFF_SIZE));
 
     //create a new managed buffer to house the data
     return managed_recv_buffer::sptr(
-        new managed_recv_buffer_impl(boost::asio::buffer(buff_mem, available))
+        new managed_recv_buffer_impl(boost::asio::buffer(recv_mem, num_bytes))
     );
 }
 
 managed_send_buffer::sptr udp_zero_copy_impl::get_send_buff(void){
-    boost::uint32_t *buff_mem = new boost::uint32_t[2000/sizeof(boost::uint32_t)];
-    return managed_send_buffer::sptr(
-        new managed_send_buffer_impl(boost::asio::buffer(buff_mem, 2000), _socket)
-    );
+    return _send_buff; //FIXME there is only ever one send buff, we assume that the caller doesnt hang onto these
 }
 
 /***********************************************************************
  * UDP zero copy make function
  **********************************************************************/
+template<typename Opt> static inline void resize_buff_helper(
+    udp_zero_copy_impl::sptr udp_trans,
+    size_t target_size,
+    const std::string &name
+){
+    //resize the buffer if size was provided
+    if (target_size > 0){
+        size_t actual_size = udp_trans->resize_buff<Opt>(target_size);
+        if (target_size != actual_size) std::cout << boost::format(
+            "Target %s buffer size: %d\n"
+            "Actual %s byffer size: %d"
+        ) % name % target_size % name % actual_size << std::endl;
+    }
+
+    //otherwise, ensure that the buffer is at least the minimum size
+    else if (udp_trans->get_buff_size<Opt>() < MIN_SOCK_BUFF_SIZE){
+        resize_buff_helper<Opt>(udp_trans, MIN_SOCK_BUFF_SIZE, name);
+    }
+}
+
 udp_zero_copy::sptr udp_zero_copy::make(
     const std::string &addr,
     const std::string &port,
     size_t recv_buff_size,
     size_t send_buff_size
 ){
-    boost::shared_ptr<udp_zero_copy_impl> udp_trans(new udp_zero_copy_impl(addr, port));
-
-    //resize the recv buffer if size was provided
-    if (recv_buff_size > 0){
-        size_t actual_bytes = udp_trans->resize_recv_buff(recv_buff_size);
-        if (recv_buff_size != actual_bytes) std::cout << boost::format(
-            "Target recv buffer size: %d\n"
-            "Actual recv byffer size: %d"
-        ) % recv_buff_size % actual_bytes << std::endl;
-    }
+    udp_zero_copy_impl::sptr udp_trans(new udp_zero_copy_impl(addr, port));
 
-    //resize the send buffer if size was provided
-    if (send_buff_size > 0){
-        size_t actual_bytes = udp_trans->resize_send_buff(send_buff_size);
-        if (send_buff_size != actual_bytes) std::cout << boost::format(
-            "Target send buffer size: %d\n"
-            "Actual send byffer size: %d"
-        ) % send_buff_size % actual_bytes << std::endl;
-    }
+    //call the helper to resize send and recv buffers
+    resize_buff_helper<boost::asio::socket_base::receive_buffer_size>(udp_trans, recv_buff_size, "recv");
+    resize_buff_helper<boost::asio::socket_base::send_buffer_size>   (udp_trans, send_buff_size, "send");
 
     return udp_trans;
 }
diff --git a/host/lib/transport/vrt_packet_handler.hpp b/host/lib/transport/vrt_packet_handler.hpp
new file mode 100644
index 000000000..e64e3383d
--- /dev/null
+++ b/host/lib/transport/vrt_packet_handler.hpp
@@ -0,0 +1,370 @@
+//
+// Copyright 2010 Ettus Research LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+#ifndef INCLUDED_LIBUHD_TRANSPORT_VRT_PACKET_HANDLER_HPP
+#define INCLUDED_LIBUHD_TRANSPORT_VRT_PACKET_HANDLER_HPP
+
+#include <uhd/config.hpp>
+#include <uhd/device.hpp>
+#include <uhd/types/io_type.hpp>
+#include <uhd/types/otw_type.hpp>
+#include <uhd/types/metadata.hpp>
+#include <uhd/transport/vrt.hpp>
+#include <uhd/transport/convert_types.hpp>
+#include <uhd/transport/zero_copy.hpp>
+#include <boost/asio/buffer.hpp>
+#include <boost/function.hpp>
+#include <stdexcept>
+#include <iostream>
+
+namespace vrt_packet_handler{
+
+/***********************************************************************
+ * vrt packet handler for recv
+ **********************************************************************/
+    struct recv_state{
+        //init the expected seq number
+        size_t next_packet_seq;
+
+        //state variables to handle fragments
+        uhd::transport::managed_recv_buffer::sptr managed_buff;
+        boost::asio::const_buffer copy_buff;
+        size_t fragment_offset_in_samps;
+
+        recv_state(void){
+            //first expected seq is zero
+            next_packet_seq = 0;
+
+            //initially empty copy buffer
+            copy_buff = boost::asio::buffer("", 0);
+        }
+    };
+
+    typedef boost::function<void(uhd::transport::managed_recv_buffer::sptr)> recv_cb_t;
+
+    static UHD_INLINE void recv_cb_nop(uhd::transport::managed_recv_buffer::sptr){
+        /* NOP */
+    }
+
+    /*******************************************************************
+     * Unpack a received vrt header and set the copy buffer.
+     *  - helper function for vrt_packet_handler::_recv1
+     ******************************************************************/
+    static UHD_INLINE void _recv1_helper(
+        recv_state &state,
+        uhd::rx_metadata_t &metadata,
+        double tick_rate,
+        size_t vrt_header_offset_words32
+    ){
+        size_t num_packet_words32 = state.managed_buff->size()/sizeof(boost::uint32_t);
+        if (num_packet_words32 <= vrt_header_offset_words32){
+            state.copy_buff = boost::asio::buffer("", 0);
+            return; //must exit here after setting the buffer
+        }
+        const boost::uint32_t *vrt_hdr = state.managed_buff->cast<const boost::uint32_t *>() + vrt_header_offset_words32;
+        size_t num_header_words32_out, num_payload_words32_out, packet_count_out;
+        uhd::transport::vrt::unpack(
+            metadata,                //output
+            vrt_hdr,                 //input
+            num_header_words32_out,  //output
+            num_payload_words32_out, //output
+            num_packet_words32,      //input
+            packet_count_out,        //output
+            tick_rate
+        );
+
+        //handle the packet count / sequence number
+        if (packet_count_out != state.next_packet_seq){
+            std::cerr << "S" << (packet_count_out - state.next_packet_seq)%16;
+        }
+        state.next_packet_seq = (packet_count_out+1)%16;
+
+        //setup the buffer to point to the data
+        state.copy_buff = boost::asio::buffer(
+            vrt_hdr + num_header_words32_out,
+            num_payload_words32_out*sizeof(boost::uint32_t)
+        );
+    }
+
+    /*******************************************************************
+     * Recv data, unpack a vrt header, and copy-convert the data.
+     *  - helper function for vrt_packet_handler::recv
+     ******************************************************************/
+    static UHD_INLINE size_t _recv1(
+        recv_state &state,
+        void *recv_mem,
+        size_t total_samps,
+        uhd::rx_metadata_t &metadata,
+        const uhd::io_type_t &io_type,
+        const uhd::otw_type_t &otw_type,
+        double tick_rate,
+        uhd::transport::zero_copy_if::sptr zc_iface,
+        //use these two params to handle a layer above vrt
+        size_t vrt_header_offset_words32,
+        const recv_cb_t& recv_cb
+    ){
+        //perform a receive if no rx data is waiting to be copied
+        if (boost::asio::buffer_size(state.copy_buff) == 0){
+            state.fragment_offset_in_samps = 0;
+            state.managed_buff = zc_iface->get_recv_buff();
+            recv_cb(state.managed_buff); //callback before vrt unpack
+            try{
+                _recv1_helper(
+                    state, metadata, tick_rate, vrt_header_offset_words32
+                );
+            }catch(const std::exception &e){
+                std::cerr << "Error (recv): " << e.what() << std::endl;
+                return 0;
+            }
+        }
+
+        //extract the number of samples available to copy
+        size_t bytes_per_item = otw_type.get_sample_size();
+        size_t bytes_available = boost::asio::buffer_size(state.copy_buff);
+        size_t num_samps = std::min(total_samps, bytes_available/bytes_per_item);
+
+        //setup the fragment flags and offset
+        metadata.more_fragments = total_samps < num_samps;
+        metadata.fragment_offset = state.fragment_offset_in_samps;
+        state.fragment_offset_in_samps += num_samps; //set for next call
+
+        //copy-convert the samples from the recv buffer
+        uhd::transport::convert_otw_type_to_io_type(
+            boost::asio::buffer_cast<const void*>(state.copy_buff), otw_type,
+            recv_mem, io_type, num_samps
+        );
+
+        //update the rx copy buffer to reflect the bytes copied
+        size_t bytes_copied = num_samps*bytes_per_item;
+        state.copy_buff = boost::asio::buffer(
+            boost::asio::buffer_cast<const boost::uint8_t*>(state.copy_buff) + bytes_copied,
+            bytes_available - bytes_copied
+        );
+
+        return num_samps;
+    }
+
+    /*******************************************************************
+     * Recv vrt packets and copy convert the samples into the buffer.
+     ******************************************************************/
+    static UHD_INLINE size_t recv(
+        recv_state &state,
+        const boost::asio::mutable_buffer &buff,
+        uhd::rx_metadata_t &metadata,
+        uhd::device::recv_mode_t recv_mode,
+        const uhd::io_type_t &io_type,
+        const uhd::otw_type_t &otw_type,
+        double tick_rate,
+        uhd::transport::zero_copy_if::sptr zc_iface,
+        //use these two params to handle a layer above vrt
+        size_t vrt_header_offset_words32 = 0,
+        const recv_cb_t& recv_cb = &recv_cb_nop
+    ){
+        metadata = uhd::rx_metadata_t(); //init the metadata
+        const size_t total_num_samps = boost::asio::buffer_size(buff)/io_type.size;
+
+        switch(recv_mode){
+
+        ////////////////////////////////////////////////////////////////
+        case uhd::device::RECV_MODE_ONE_PACKET:{
+        ////////////////////////////////////////////////////////////////
+            return _recv1(
+                state,
+                boost::asio::buffer_cast<void *>(buff),
+                total_num_samps,
+                metadata,
+                io_type, otw_type,
+                tick_rate,
+                zc_iface,
+                vrt_header_offset_words32,
+                recv_cb
+            );
+        }
+
+        ////////////////////////////////////////////////////////////////
+        case uhd::device::RECV_MODE_FULL_BUFF:{
+        ////////////////////////////////////////////////////////////////
+            size_t accum_num_samps = 0;
+            uhd::rx_metadata_t tmp_md;
+            while(accum_num_samps < total_num_samps){
+                size_t num_samps = _recv1(
+                    state,
+                    boost::asio::buffer_cast<boost::uint8_t *>(buff) + (accum_num_samps*io_type.size),
+                    total_num_samps - accum_num_samps,
+                    (accum_num_samps == 0)? metadata : tmp_md, //only the first metadata gets kept
+                    io_type, otw_type,
+                    tick_rate,
+                    zc_iface,
+                    vrt_header_offset_words32,
+                    recv_cb
+                );
+                if (num_samps == 0) break; //had a recv timeout or error, break loop
+                accum_num_samps += num_samps;
+            }
+            return accum_num_samps;
+        }
+
+        default: throw std::runtime_error("unknown recv mode");
+        }//switch(recv_mode)
+    }
+
+/***********************************************************************
+ * vrt packet handler for send
+ **********************************************************************/
+    struct send_state{
+        //init the expected seq number
+        size_t next_packet_seq;
+
+        send_state(void){
+            next_packet_seq = 0;
+        }
+    };
+
+    typedef boost::function<void(uhd::transport::managed_send_buffer::sptr)> send_cb_t;
+
+    static UHD_INLINE void send_cb_nop(uhd::transport::managed_send_buffer::sptr){
+        /* NOP */
+    }
+
+    /*******************************************************************
+     * Pack a vrt header, copy-convert the data, and send it.
+     *  - helper function for vrt_packet_handler::send
+     ******************************************************************/
+    static UHD_INLINE void _send1(
+        send_state &state,
+        const void *send_mem,
+        size_t num_samps,
+        const uhd::tx_metadata_t &metadata,
+        const uhd::io_type_t &io_type,
+        const uhd::otw_type_t &otw_type,
+        double tick_rate,
+        uhd::transport::zero_copy_if::sptr zc_iface,
+        size_t vrt_header_offset_words32,
+        const send_cb_t& send_cb
+    ){
+        //get a new managed send buffer
+        uhd::transport::managed_send_buffer::sptr send_buff = zc_iface->get_send_buff();
+        boost::uint32_t *tx_mem = send_buff->cast<boost::uint32_t *>() + vrt_header_offset_words32;
+
+        size_t num_header_words32, num_packet_words32;
+        size_t packet_count = state.next_packet_seq++;
+
+        //pack metadata into a vrt header
+        uhd::transport::vrt::pack(
+            metadata,            //input
+            tx_mem,              //output
+            num_header_words32,  //output
+            num_samps,           //input
+            num_packet_words32,  //output
+            packet_count,        //input
+            tick_rate
+        );
+
+        //copy-convert the samples into the send buffer
+        uhd::transport::convert_io_type_to_otw_type(
+            send_mem, io_type,
+            tx_mem + num_header_words32, otw_type,
+            num_samps
+        );
+
+        send_cb(send_buff); //callback after memory filled
+
+        //commit the samples to the zero-copy interface
+        send_buff->commit(num_packet_words32*sizeof(boost::uint32_t));
+    }
+
+    /*******************************************************************
+     * Send vrt packets and copy convert the samples into the buffer.
+     ******************************************************************/
+    static UHD_INLINE size_t send(
+        send_state &state,
+        const boost::asio::const_buffer &buff,
+        const uhd::tx_metadata_t &metadata,
+        uhd::device::send_mode_t send_mode,
+        const uhd::io_type_t &io_type,
+        const uhd::otw_type_t &otw_type,
+        double tick_rate,
+        uhd::transport::zero_copy_if::sptr zc_iface,
+        size_t max_samples_per_packet,
+        //use these two params to handle a layer above vrt
+        size_t vrt_header_offset_words32 = 0,
+        const send_cb_t& send_cb = &send_cb_nop
+    ){
+        const size_t total_num_samps = boost::asio::buffer_size(buff)/io_type.size;
+        if (total_num_samps <= max_samples_per_packet) send_mode = uhd::device::SEND_MODE_ONE_PACKET;
+        switch(send_mode){
+
+        ////////////////////////////////////////////////////////////////
+        case uhd::device::SEND_MODE_ONE_PACKET:{
+        ////////////////////////////////////////////////////////////////
+            size_t num_samps = std::min(total_num_samps, max_samples_per_packet);
+            _send1(
+                state,
+                boost::asio::buffer_cast<const void *>(buff),
+                num_samps,
+                metadata,
+                io_type, otw_type,
+                tick_rate,
+                zc_iface,
+                vrt_header_offset_words32,
+                send_cb
+            );
+            return num_samps;
+        }
+
+        ////////////////////////////////////////////////////////////////
+        case uhd::device::SEND_MODE_FULL_BUFF:{
+        ////////////////////////////////////////////////////////////////
+            //calculate constants for fragmentation
+            const size_t num_fragments = (total_num_samps+max_samples_per_packet-1)/max_samples_per_packet;
+            static const size_t first_fragment_index = 0;
+            const size_t final_fragment_index = num_fragments-1;
+
+            //make a rw copy of the metadata to re-flag below
+            uhd::tx_metadata_t md(metadata);
+
+            //loop through the following fragment indexes
+            for (size_t n = first_fragment_index; n <= final_fragment_index; n++){
+
+                //calculate new flags for the fragments
+                md.has_time_spec  = metadata.has_time_spec  and (n == first_fragment_index);
+                md.start_of_burst = metadata.start_of_burst and (n == first_fragment_index);
+                md.end_of_burst   = metadata.end_of_burst   and (n == final_fragment_index);
+
+                //send the fragment with the helper function
+                _send1(
+                    state,
+                    boost::asio::buffer_cast<const boost::uint8_t *>(buff) + (n*max_samples_per_packet*io_type.size),
+                    (n == final_fragment_index)?(total_num_samps%max_samples_per_packet):max_samples_per_packet,
+                    md,
+                    io_type, otw_type,
+                    tick_rate,
+                    zc_iface,
+                    vrt_header_offset_words32,
+                    send_cb
+                );
+            }
+            return total_num_samps;
+        }
+
+        default: throw std::runtime_error("unknown send mode");
+        }//switch(send_mode)
+    }
+
+} //namespace vrt_packet_handler
+
+#endif /* INCLUDED_LIBUHD_TRANSPORT_VRT_PACKET_HANDLER_HPP */