//
// Copyright 2019 Ettus Research, a National Instruments Brand
//
// SPDX-License-Identifier: GPL-3.0-or-later
//

#include "x300_eth_mgr.hpp"
#include "x300_claim.hpp"
#include "x300_defaults.hpp"
#include "x300_device_args.hpp"
#include "x300_fw_common.h"
#include "x300_mb_eeprom.hpp"
#include "x300_mb_eeprom_iface.hpp"
#include "x300_regs.hpp"
#include <uhd/exception.hpp>
#include <uhd/rfnoc/defaults.hpp>
#include <uhd/transport/if_addrs.hpp>
#include <uhd/transport/udp_constants.hpp>
#include <uhd/transport/udp_simple.hpp>
#include <uhd/transport/udp_zero_copy.hpp>
#include <uhd/utils/algorithm.hpp>
#include <uhd/utils/byteswap.hpp>
#include <uhdlib/rfnoc/device_id.hpp>
#include <uhdlib/rfnoc/rfnoc_common.hpp>
#include <uhdlib/transport/udp_boost_asio_link.hpp>
#include <uhdlib/transport/udp_common.hpp>
#include <uhdlib/usrp/cores/i2c_core_100_wb32.hpp>
#ifdef HAVE_DPDK
#    include <uhdlib/transport/dpdk_simple.hpp>
#    include <uhdlib/transport/udp_dpdk_link.hpp>
#endif
#include <boost/asio.hpp>
#include <string>

uhd::wb_iface::sptr x300_make_ctrl_iface_enet(
    uhd::transport::udp_simple::sptr udp, bool enable_errors = true);

using namespace uhd;
using namespace uhd::usrp;
using namespace uhd::rfnoc;
using namespace uhd::transport;
using namespace uhd::usrp::x300;
namespace asio = boost::asio;

namespace {

constexpr unsigned int X300_UDP_RESERVED_FRAME_SIZE = 64;
constexpr size_t XGE_DATA_FRAME_SEND_SIZE           = 8972;
constexpr size_t XGE_DATA_FRAME_RECV_SIZE           = 8972;
constexpr size_t GE_DATA_FRAME_SEND_SIZE            = 1472;
constexpr size_t GE_DATA_FRAME_RECV_SIZE            = 1472;
constexpr size_t ETH_MSG_NUM_FRAMES                 = 64;

// Default for num data frames is set to a value that will work well when send
// or recv offload is enabled, or when using DPDK.
constexpr size_t ETH_DATA_NUM_FRAMES = 32;

constexpr size_t ETH_MSG_FRAME_SIZE = uhd::transport::udp_simple::mtu; // bytes
constexpr size_t MAX_RATE_10GIGE    = (size_t)( // bytes/s
    10e9 / 8 * // wire speed multiplied by percentage of packets that is sample data
    (float(x300::DATA_FRAME_MAX_SIZE - CHDR_MAX_LEN_HDR)
        / float(x300::DATA_FRAME_MAX_SIZE
                + 8 /* UDP header */ + 20 /* Ethernet header length */)));
constexpr size_t MAX_RATE_1GIGE     = (size_t)( // bytes/s
    10e9 / 8 * // wire speed multiplied by percentage of packets that is sample data
    (float(GE_DATA_FRAME_RECV_SIZE - CHDR_MAX_LEN_HDR)
        / float(GE_DATA_FRAME_RECV_SIZE
                + 8 /* UDP header */ + 20 /* Ethernet header length */)));


} // namespace

/******************************************************************************
 * Static Methods
 *****************************************************************************/
eth_manager::udp_simple_factory_t eth_manager::x300_get_udp_factory(const bool use_dpdk)
{
    udp_simple_factory_t udp_make_connected = udp_simple::make_connected;
    if (use_dpdk) {
#ifdef HAVE_DPDK
        udp_make_connected = [](const std::string& addr, const std::string& port) {
            return dpdk_simple::make_connected(addr, port);
        };
#else
        UHD_LOG_WARNING(
            "DPDK", "Detected use_dpdk argument, but DPDK support not built in.");
#endif
    }
    return udp_make_connected;
}

device_addrs_t eth_manager::find(const device_addr_t& hint)
{
    bool use_dpdk          = hint.has_key("use_dpdk");
    std::string first_addr = hint.has_key("addr") ? hint["addr"] : "";

    udp_simple_factory_t udp_make_broadcast = udp_simple::make_broadcast;
    udp_simple_factory_t udp_make_connected = x300_get_udp_factory(use_dpdk);
#ifdef HAVE_DPDK
    if (use_dpdk) {
        auto dpdk_ctx = uhd::transport::dpdk::dpdk_ctx::get();
        if (not dpdk_ctx->is_init_done()) {
            dpdk_ctx->init(hint);
        }
        udp_make_broadcast = dpdk_simple::make_broadcast;
    }
#endif
    udp_simple::sptr comm =
        udp_make_broadcast(first_addr, BOOST_STRINGIZE(X300_FW_COMMS_UDP_PORT));

    // load request struct
    x300_fw_comms_t request = x300_fw_comms_t();
    request.flags           = uhd::htonx<uint32_t>(X300_FW_COMMS_FLAGS_ACK);
    request.sequence        = uhd::htonx<uint32_t>(std::rand());

    // send request
    comm->send(asio::buffer(&request, sizeof(request)));

    // loop for replies until timeout
    device_addrs_t addrs;
    while (true) {
        char buff[X300_FW_COMMS_MTU] = {};
        const size_t nbytes          = comm->recv(asio::buffer(buff), 0.050);
        if (nbytes == 0)
            break;
        const x300_fw_comms_t* reply = (const x300_fw_comms_t*)buff;
        if (request.flags != reply->flags)
            continue;
        if (request.sequence != reply->sequence)
            continue;
        device_addr_t new_addr;
        new_addr["type"] = "x300";
        new_addr["addr"] = comm->get_recv_addr();

        // Attempt to read the name from the EEPROM and perform filtering.
        // This operation can throw due to compatibility mismatch.
        try {
            wb_iface::sptr zpu_ctrl = x300_make_ctrl_iface_enet(
                udp_make_connected(
                    new_addr["addr"], BOOST_STRINGIZE(X300_FW_COMMS_UDP_PORT)),
                false /* Suppress timeout errors */
            );

            new_addr["fpga"] = get_fpga_option(zpu_ctrl);

            i2c_core_100_wb32::sptr zpu_i2c =
                i2c_core_100_wb32::make(zpu_ctrl, I2C1_BASE);
            x300_mb_eeprom_iface::sptr eeprom_iface =
                x300_mb_eeprom_iface::make(zpu_ctrl, zpu_i2c);
            const mboard_eeprom_t mb_eeprom = get_mb_eeprom(eeprom_iface);
            if (mb_eeprom.size() == 0 or claim_status(zpu_ctrl) == CLAIMED_BY_OTHER) {
                // Skip device claimed by another process
                continue;
            }
            new_addr["name"]   = mb_eeprom["name"];
            new_addr["serial"] = mb_eeprom["serial"];
            const std::string product_name =
                map_mb_type_to_product_name(get_mb_type_from_eeprom(mb_eeprom));
            if (!product_name.empty()) {
                new_addr["product"] = product_name;
            }
        } catch (const std::exception&) {
            // set these values as empty string so the device may still be found
            // and the filter's below can still operate on the discovered device
            new_addr["name"]   = "";
            new_addr["serial"] = "";
        }
        // filter the discovered device below by matching optional keys
        if ((not hint.has_key("name") or hint["name"] == new_addr["name"])
            and (not hint.has_key("serial") or hint["serial"] == new_addr["serial"])
            and (not hint.has_key("product") or hint["product"] == new_addr["product"])) {
            addrs.push_back(new_addr);
        }
    }

    return addrs;
}

/******************************************************************************
 * Structors
 *****************************************************************************/
eth_manager::eth_manager(
    const x300_device_args_t& args, uhd::property_tree::sptr, const uhd::fs_path&)
    : _args(args)
{
    UHD_ASSERT_THROW(!args.get_first_addr().empty());

    auto dev_addr = args.get_orig_args();
    for (const std::string& key : dev_addr.keys()) {
        if (key.find("recv") != std::string::npos)
            recv_args[key] = dev_addr[key];
        if (key.find("send") != std::string::npos)
            send_args[key] = dev_addr[key];
    }

    // Initially store only the first address provided to setup communication
    // Once we read the EEPROM, we use it to map IP to its interface
    // In discover_eth(), we'll check and enable the other IP address, if given
    x300_eth_conn_t init;
    init.addr      = args.get_first_addr();
    auto device_id = allocate_device_id();
    _local_device_ids.push_back(device_id);
    eth_conns[device_id] = init;

    _x300_make_udp_connected = x300_get_udp_factory(args.get_use_dpdk());
}

both_links_t eth_manager::get_links(link_type_t link_type,
    const device_id_t local_device_id,
    const sep_id_t& /*local_epid*/,
    const sep_id_t& /*remote_epid*/,
    const device_addr_t& link_args)
{
    if (!uhd::has(_local_device_ids, local_device_id)) {
        const std::string err_msg =
            std::string("Cannot create Ethernet link through local device ID ")
            + std::to_string(local_device_id)
            + ", no such device associated with this motherboard!";
        UHD_LOG_ERROR("X300", err_msg);
        throw uhd::runtime_error(err_msg);
    }
    // FIXME: We now need to properly associate local_device_id with the right
    // entry in eth_conn. We should probably do the load balancing elsewhere,
    // and do something like this:
    // However, we might also have to make sure that we don't do 2x TX through
    // a DMA FIFO, which is a device-specific thing. So punt on that for now.

    x300_eth_conn_t conn = eth_conns[local_device_id];
    zero_copy_xport_params default_buff_args;

    const size_t send_mtu = get_mtu(uhd::TX_DIRECTION);
    const size_t recv_mtu = get_mtu(uhd::RX_DIRECTION);

    // Set size and number of frames
    default_buff_args.send_frame_size = std::min(send_mtu, ETH_MSG_FRAME_SIZE);
    default_buff_args.recv_frame_size = std::min(recv_mtu, ETH_MSG_FRAME_SIZE);

    // Buffering is done in the socket buffers, so size them relative to
    // the link rate
    link_params_t default_link_params;
    default_link_params.num_send_frames = ETH_DATA_NUM_FRAMES;
    default_link_params.num_recv_frames = ETH_DATA_NUM_FRAMES;
    default_link_params.send_frame_size = conn.link_rate == MAX_RATE_1GIGE
                                              ? GE_DATA_FRAME_SEND_SIZE
                                              : XGE_DATA_FRAME_SEND_SIZE;
    default_link_params.recv_frame_size = conn.link_rate == MAX_RATE_1GIGE
                                              ? GE_DATA_FRAME_RECV_SIZE
                                              : XGE_DATA_FRAME_RECV_SIZE;
    default_link_params.send_buff_size = conn.link_rate / 50;
    default_link_params.recv_buff_size = std::max(conn.link_rate / 50,
        ETH_MSG_NUM_FRAMES * ETH_MSG_FRAME_SIZE); // enough to hold greater of 20 ms or
                                                  // number of msg frames

    link_params_t link_params = calculate_udp_link_params(link_type,
        get_mtu(uhd::TX_DIRECTION),
        get_mtu(uhd::RX_DIRECTION),
        default_link_params,
        _args.get_orig_args(),
        link_args);

    // Enforce a minimum bound of the number of receive and send frames.
    link_params.num_send_frames =
        std::max(uhd::rfnoc::MIN_NUM_FRAMES, link_params.num_send_frames);
    link_params.num_recv_frames =
        std::max(uhd::rfnoc::MIN_NUM_FRAMES, link_params.num_recv_frames);

    if (_args.get_use_dpdk()) {
#ifdef HAVE_DPDK
        auto link = uhd::transport::udp_dpdk_link::make(
            conn.addr, BOOST_STRINGIZE(X300_VITA_UDP_PORT), link_params);
        return std::make_tuple(link,
            link_params.send_buff_size,
            link,
            link_params.recv_buff_size,
            true,
            true);
#else
        UHD_LOG_WARNING("X300", "Cannot create DPDK transport, falling back to UDP");
#endif
    }
    auto link = uhd::transport::udp_boost_asio_link::make(conn.addr,
        BOOST_STRINGIZE(X300_VITA_UDP_PORT),
        link_params,
        link_params.recv_buff_size,
        link_params.send_buff_size);
    return std::make_tuple(
        link, link_params.send_buff_size, link, link_params.recv_buff_size, true, false);
}

/******************************************************************************
 * API
 *****************************************************************************/
wb_iface::sptr eth_manager::get_ctrl_iface()
{
    return x300_make_ctrl_iface_enet(_x300_make_udp_connected(
        get_pri_eth().addr, BOOST_STRINGIZE(X300_FW_COMMS_UDP_PORT)));
}

// - Populates _max_frame_sizes
void eth_manager::init_link(
    const mboard_eeprom_t& mb_eeprom, const std::string& loaded_fpga_image)
{
    // Discover ethernet interfaces on the device
    discover_eth(mb_eeprom, loaded_fpga_image);

    /* This is an ETH connection. Figure out what the maximum supported frame
     * size is for the transport in the up and down directions. The frame size
     * depends on the host PC's NIC's MTU settings. To determine the frame size,
     * we test for support up to an expected "ceiling". If the user
     * specified a frame size, we use that frame size as the ceiling. If no
     * frame size was specified, we use the maximum UHD frame size.
     *
     * To optimize performance, the frame size should be greater than or equal
     * to the frame size that UHD uses so that frames don't get split across
     * multiple transmission units - this is why the limits passed into the
     * 'determine_max_frame_size' function are actually frame sizes. */
    frame_size_t req_max_frame_size;
    req_max_frame_size.recv_frame_size =
        (recv_args.has_key("recv_frame_size"))
            ? boost::lexical_cast<size_t>(recv_args["recv_frame_size"])
            : x300::DATA_FRAME_MAX_SIZE;
    req_max_frame_size.send_frame_size =
        (send_args.has_key("send_frame_size"))
            ? boost::lexical_cast<size_t>(send_args["send_frame_size"])
            : x300::DATA_FRAME_MAX_SIZE;

#if defined UHD_PLATFORM_LINUX
    const std::string mtu_tool("ip link");
#elif defined UHD_PLATFORM_WIN32
    const std::string mtu_tool("netsh");
#else
    const std::string mtu_tool("ifconfig");
#endif

    // Detect the frame size on the path to the USRP
    try {
        frame_size_t pri_frame_sizes =
            determine_max_frame_size(get_pri_eth().addr, req_max_frame_size);

        _max_frame_sizes = pri_frame_sizes;
        if (_local_device_ids.size() > 1) {
            frame_size_t sec_frame_sizes = determine_max_frame_size(
                eth_conns.at(_local_device_ids.at(1)).addr, req_max_frame_size);

            // Choose the minimum of the max frame sizes
            // to ensure we don't exceed any one of the links' MTU
            _max_frame_sizes.recv_frame_size = std::min(
                pri_frame_sizes.recv_frame_size, sec_frame_sizes.recv_frame_size);

            _max_frame_sizes.send_frame_size = std::min(
                pri_frame_sizes.send_frame_size, sec_frame_sizes.send_frame_size);
        }
    } catch (std::exception& e) {
        UHD_LOGGER_ERROR("X300") << e.what();
    }

    // Check actual frame sizes against user-requested frame sizes, and print
    // warnings if they don't match
    if ((recv_args.has_key("recv_frame_size"))
        && (req_max_frame_size.recv_frame_size > _max_frame_sizes.recv_frame_size)) {
        UHD_LOGGER_WARNING("X300")
            << boost::format("You requested a receive frame size of (%lu) but your "
                             "NIC's max frame size is (%lu).")
                   % req_max_frame_size.recv_frame_size % _max_frame_sizes.recv_frame_size
            << boost::format("Please verify your NIC's MTU setting using '%s' or set "
                             "the recv_frame_size argument appropriately.")
                   % mtu_tool
            << "UHD will use the auto-detected max frame size for this connection.";
    }

    if ((send_args.has_key("send_frame_size"))
        && (req_max_frame_size.send_frame_size > _max_frame_sizes.send_frame_size)) {
        UHD_LOGGER_WARNING("X300")
            << boost::format("You requested a send frame size of (%lu) but your "
                             "NIC's max frame size is (%lu).")
                   % req_max_frame_size.send_frame_size % _max_frame_sizes.send_frame_size
            << boost::format("Please verify your NIC's MTU setting using '%s' or set "
                             "the send_frame_size argument appropriately.")
                   % mtu_tool
            << "UHD will use the auto-detected max frame size for this connection.";
    }

    // Check actual frame sizes against detected frame sizes, and print
    // warnings if they don't match
    for (auto conn_pair : eth_conns) {
        auto conn                  = conn_pair.second;
        size_t rec_send_frame_size = conn.link_rate == MAX_RATE_1GIGE
                                         ? GE_DATA_FRAME_SEND_SIZE
                                         : XGE_DATA_FRAME_SEND_SIZE;
        size_t rec_recv_frame_size = conn.link_rate == MAX_RATE_1GIGE
                                         ? GE_DATA_FRAME_RECV_SIZE
                                         : XGE_DATA_FRAME_RECV_SIZE;

        if (_max_frame_sizes.send_frame_size < rec_send_frame_size) {
            UHD_LOGGER_WARNING("X300")
                << boost::format("For the %s connection, UHD recommends a send frame "
                                 "size of at least %lu for best\nperformance, but "
                                 "your configuration will only allow %lu.")
                       % conn.addr % rec_send_frame_size
                       % _max_frame_sizes.send_frame_size
                << "This may negatively impact your maximum achievable sample "
                   "rate.\nCheck the MTU on the interface and/or the send_frame_size "
                   "argument.";
        }

        if (_max_frame_sizes.recv_frame_size < rec_recv_frame_size) {
            UHD_LOGGER_WARNING("X300")
                << boost::format("For the %s connection, UHD recommends a receive "
                                 "frame size of at least %lu for best\nperformance, "
                                 "but your configuration will only allow %lu.")
                       % conn.addr % rec_recv_frame_size
                       % _max_frame_sizes.recv_frame_size
                << "This may negatively impact your maximum achievable sample "
                   "rate.\nCheck the MTU on the interface and/or the recv_frame_size "
                   "argument.";
        }
    }
}

size_t eth_manager::get_mtu(uhd::direction_t dir)
{
    return dir == uhd::RX_DIRECTION ? _max_frame_sizes.recv_frame_size
                                    : _max_frame_sizes.send_frame_size;
}


void eth_manager::discover_eth(
    const mboard_eeprom_t mb_eeprom, const std::string& loaded_fpga_image)
{
    udp_simple_factory_t udp_make_connected = x300_get_udp_factory(_args.get_use_dpdk());
    // Load all valid, non-duplicate IP addrs
    std::vector<std::string> ip_addrs{_args.get_first_addr()};
    if (not _args.get_second_addr().empty()
        && (_args.get_first_addr() != _args.get_second_addr())) {
        ip_addrs.push_back(_args.get_second_addr());
    }

    // Grab the device ID used during init
    auto init_dev_id = _local_device_ids.at(0);

    // Index the MB EEPROM addresses
    std::vector<std::string> mb_eeprom_addrs;
    const size_t num_mb_eeprom_addrs = 4;
    for (size_t i = 0; i < num_mb_eeprom_addrs; i++) {
        const std::string key = "ip-addr" + std::to_string(i);

        // Show a warning if there exists duplicate addresses in the mboard eeprom
        if (std::find(mb_eeprom_addrs.begin(), mb_eeprom_addrs.end(), mb_eeprom[key])
            != mb_eeprom_addrs.end()) {
            UHD_LOGGER_WARNING("X300") << str(
                boost::format(
                    "Duplicate IP address %s found in mboard EEPROM. "
                    "Device may not function properly. View and reprogram the values "
                    "using the usrp_burn_mb_eeprom utility.")
                % mb_eeprom[key]);
        }
        mb_eeprom_addrs.push_back(mb_eeprom[key]);
    }

    for (const std::string& addr : ip_addrs) {
        x300_eth_conn_t conn_iface;
        conn_iface.addr = addr;
        conn_iface.type = X300_IFACE_NONE;

        // Decide from the mboard eeprom what IP corresponds
        // to an interface
        for (size_t i = 0; i < mb_eeprom_addrs.size(); i++) {
            if (addr == mb_eeprom_addrs[i]) {
                // Choose the interface based on the index parity
                if (i % 2 == 0) {
                    conn_iface.type      = X300_IFACE_ETH0;
                    conn_iface.link_rate = loaded_fpga_image == "HG" ? MAX_RATE_1GIGE
                                                                     : MAX_RATE_10GIGE;
                } else {
                    conn_iface.type      = X300_IFACE_ETH1;
                    conn_iface.link_rate = MAX_RATE_10GIGE;
                }
                break;
            }
        }

        // Check default IP addresses if we couldn't
        // determine the IP from the mboard eeprom
        if (conn_iface.type == X300_IFACE_NONE) {
            UHD_LOGGER_WARNING("X300") << str(
                boost::format(
                    "Address %s not found in mboard EEPROM. Address may be wrong or "
                    "the EEPROM may be corrupt. Attempting to continue with default "
                    "IP addresses.")
                % conn_iface.addr);

            if (addr
                == boost::asio::ip::address_v4(uint32_t(X300_DEFAULT_IP_ETH0_1G))
                       .to_string()) {
                conn_iface.type      = X300_IFACE_ETH0;
                conn_iface.link_rate = MAX_RATE_1GIGE;
            } else if (addr
                       == boost::asio::ip::address_v4(uint32_t(X300_DEFAULT_IP_ETH1_1G))
                              .to_string()) {
                conn_iface.type      = X300_IFACE_ETH1;
                conn_iface.link_rate = MAX_RATE_1GIGE;
            } else if (addr
                       == boost::asio::ip::address_v4(uint32_t(X300_DEFAULT_IP_ETH0_10G))
                              .to_string()) {
                conn_iface.type      = X300_IFACE_ETH0;
                conn_iface.link_rate = MAX_RATE_10GIGE;
            } else if (addr
                       == boost::asio::ip::address_v4(uint32_t(X300_DEFAULT_IP_ETH1_10G))
                              .to_string()) {
                conn_iface.type      = X300_IFACE_ETH1;
                conn_iface.link_rate = MAX_RATE_10GIGE;
            } else {
                throw uhd::assertion_error(
                    str(boost::format(
                            "X300 Initialization Error: Failed to match address %s with "
                            "any addresses for the device. Please check the address.")
                        % conn_iface.addr));
            }
        }

        // Save to a vector of connections
        if (conn_iface.type != X300_IFACE_NONE) {
            // Check the address before we add it
            try {
                wb_iface::sptr zpu_ctrl = x300_make_ctrl_iface_enet(
                    udp_make_connected(
                        conn_iface.addr, BOOST_STRINGIZE(X300_FW_COMMS_UDP_PORT)),
                    false /* Suppress timeout errors */
                );

                // Peek the ZPU ctrl to make sure this connection works
                zpu_ctrl->peek32(0);
            }

            // If the address does not work, throw an error
            catch (std::exception&) {
                throw uhd::io_error(
                    str(boost::format("X300 Initialization Error: Invalid address %s")
                        % conn_iface.addr));
            }
            if (conn_iface.addr == eth_conns.at(init_dev_id).addr) {
                eth_conns[init_dev_id] = conn_iface;
            } else {
                auto device_id = allocate_device_id();
                _local_device_ids.push_back(device_id);
                eth_conns[device_id] = conn_iface;
            }
        }
    }

    if (eth_conns.size() == 0) {
        throw uhd::assertion_error(
            "X300 Initialization Error: No valid Ethernet interfaces specified.");
    }
}

eth_manager::frame_size_t eth_manager::determine_max_frame_size(
    const std::string& addr, const frame_size_t& user_frame_size)
{
    auto udp = _x300_make_udp_connected(addr, BOOST_STRINGIZE(X300_MTU_DETECT_UDP_PORT));

    std::vector<uint8_t> buffer(
        std::max(user_frame_size.recv_frame_size, user_frame_size.send_frame_size));
    x300_mtu_t* request           = reinterpret_cast<x300_mtu_t*>(&buffer.front());
    constexpr double echo_timeout = 0.020; // 20 ms

    // test holler - check if its supported in this fw version
    request->flags = uhd::htonx<uint32_t>(X300_MTU_DETECT_ECHO_REQUEST);
    request->size  = uhd::htonx<uint32_t>(sizeof(x300_mtu_t));
    udp->send(boost::asio::buffer(buffer, sizeof(x300_mtu_t)));
    udp->recv(boost::asio::buffer(buffer), echo_timeout);
    if (!(uhd::ntohx<uint32_t>(request->flags) & X300_MTU_DETECT_ECHO_REPLY)) {
        throw uhd::not_implemented_error("Holler protocol not implemented");
    }

    // Reducing range of (min,max) by setting max value to 10gig max_frame_size as larger
    // sizes are not supported
    size_t min_recv_frame_size = sizeof(x300_mtu_t);
    size_t max_recv_frame_size =
        std::min(user_frame_size.recv_frame_size, x300::DATA_FRAME_MAX_SIZE) & size_t(~3);
    size_t min_send_frame_size = sizeof(x300_mtu_t);
    size_t max_send_frame_size =
        std::min(user_frame_size.send_frame_size, x300::DATA_FRAME_MAX_SIZE) & size_t(~3);

    UHD_LOGGER_DEBUG("X300") << "Determining maximum frame size... ";
    while (min_recv_frame_size < max_recv_frame_size) {
        size_t test_frame_size = (max_recv_frame_size / 2 + min_recv_frame_size / 2 + 3)
                                 & ~3;

        request->flags = uhd::htonx<uint32_t>(X300_MTU_DETECT_ECHO_REQUEST);
        request->size  = uhd::htonx<uint32_t>(test_frame_size);
        udp->send(boost::asio::buffer(buffer, sizeof(x300_mtu_t)));

        size_t len = udp->recv(boost::asio::buffer(buffer), echo_timeout);

        if (len >= test_frame_size)
            min_recv_frame_size = test_frame_size;
        else
            max_recv_frame_size = test_frame_size - 4;
    }

    if (min_recv_frame_size < IP_PROTOCOL_MIN_MTU_SIZE - IP_PROTOCOL_UDP_PLUS_IP_HEADER) {
        throw uhd::runtime_error("System receive MTU size is less than the minimum "
                                 "required by the IP protocol.");
    }

    while (min_send_frame_size < max_send_frame_size) {
        size_t test_frame_size = (max_send_frame_size / 2 + min_send_frame_size / 2 + 3)
                                 & ~3;

        request->flags = uhd::htonx<uint32_t>(X300_MTU_DETECT_ECHO_REQUEST);
        request->size  = uhd::htonx<uint32_t>(sizeof(x300_mtu_t));
        udp->send(boost::asio::buffer(buffer, test_frame_size));

        size_t len = udp->recv(boost::asio::buffer(buffer), echo_timeout);
        if (len >= sizeof(x300_mtu_t))
            len = uhd::ntohx<uint32_t>(request->size);

        if (len >= test_frame_size)
            min_send_frame_size = test_frame_size;
        else
            max_send_frame_size = test_frame_size - 4;
    }

    if (min_send_frame_size < IP_PROTOCOL_MIN_MTU_SIZE - IP_PROTOCOL_UDP_PLUS_IP_HEADER) {
        throw uhd::runtime_error(
            "System send MTU size is less than the minimum required by the IP protocol.");
    }

    frame_size_t frame_size;
    // There are cases when NICs accept oversized packets, in which case we'd falsely
    // detect a larger-than-possible frame size. A safe and sensible value is the minimum
    // of the recv and send frame sizes.
    frame_size.recv_frame_size = std::min(min_recv_frame_size, min_send_frame_size);
    frame_size.send_frame_size = std::min(min_recv_frame_size, min_send_frame_size);
    UHD_LOGGER_INFO("X300") << "Maximum frame size: " << frame_size.send_frame_size
                            << " bytes.";
    return frame_size;
}