transmit_segment_dyn_descr_example.cpp Source File

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/**
 * @example net/transmit_segment_dyn_descr/transmit_segment_dyn_descr_example.cpp
 * @section transmit_segment_dyn_descr_example_description Description
 *
 * This example transmits 100 packets with DYN3 descriptors
 * using a network TX stream in segment interface mode.
 * The packets are transmitted on port 0.
 *
 * The example also shows how the tx_ignore command bit is used.
 *
 * While this example use DYN3 descriptors, the same functionality is possible
 * with DYN1, DYN2, DYN4, or any future dynamic descriptors with a color field.
 *
 */

// Include this in order to access the Napatech API
#include <nt.h>

#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <iostream>

/**
 * IPv4 UDP packet. No FCS included. Size: 96 byte.
 */
static constexpr uint8_t Test_packet[] {
  0xb7, 0x27, 0x53, 0x03, 0xe5, 0x8a, 0x6e, 0x97,
  0xba, 0x83, 0xa4, 0xc4, 0x08, 0x00, 0x45, 0x00,
  0x00, 0x52, 0x00, 0x01, 0x00, 0x00, 0x40, 0x11,
  0x26, 0x57, 0xfb, 0x83, 0x89, 0xd7, 0xd9, 0x4c,
  0xf5, 0x9b, 0x06, 0x09, 0xfa, 0xaa, 0x00, 0x3e,
  0xce, 0xa5, 0x70, 0x69, 0x7a, 0x7a, 0x61, 0x70,
  0x69, 0x7a, 0x7a, 0x61, 0x70, 0x69, 0x7a, 0x7a,
  0x61, 0x70, 0x69, 0x7a, 0x7a, 0x61, 0x70, 0x69,
  0x7a, 0x7a, 0x61, 0x70, 0x69, 0x7a, 0x7a, 0x61,
  0x70, 0x69, 0x7a, 0x7a, 0x61, 0x70, 0x69, 0x7a,
  0x7a, 0x61, 0x70, 0x69, 0x7a, 0x7a, 0x61, 0x70,
  0x69, 0x7a, 0x7a, 0x61, 0x70, 0x69, 0x7a, 0x7a
};

/**
 * An overlay struct for NtDyn3Descr_t making c-style or reinterpret cast possible.
 * tx_ignore: Bit position 28. Overlays bit [13] in NtDyn3Descr_t.color_lo
 */
struct Dyn3_checksum_overlay {
  uint64_t dont_care0:28;
  uint64_t tx_ignore:1;
  uint64_t dont_care1:35;
  uint64_t dont_care2;
  uint64_t dont_care3:48;
};

/**
 * Handles and prints NT error messages, and the terminates the program.
 */
static void handle_error_status(int status, const char* message)
{
  if (status != NT_SUCCESS) {
    char error_buffer[NT_ERRBUF_SIZE];
    NT_ExplainError(status, error_buffer, sizeof(error_buffer));
    std::cerr << message << ": " << error_buffer << std::endl;
    std::exit(EXIT_FAILURE);
  }
}

/**
 * Calculate the size of a segment padding packet, and add it to the net buffer.
 * Returns the size of the padding packet added (incl. descriptor size).
 */
static uint64_t create_padding_packet_dyn3(struct NtNetBuf_s& buffer,
  uint64_t max_packet_size, uint64_t remaining_segment_space)
{
  constexpr uint64_t min_packet_size = 64;
  constexpr uint64_t min_padding_size = NT_DESCR_DYN3_LENGTH + min_packet_size;

  uint64_t max_padding_size = NT_DESCR_DYN3_LENGTH + max_packet_size;
  uint16_t padding_size = 0;

  if (remaining_segment_space >= min_padding_size + max_padding_size) {
    // More than one padding packet is needed.
    // So add a padding packet with maximum size
    padding_size = static_cast<uint16_t>(max_packet_size);
  }
  else if (remaining_segment_space <= max_padding_size) {
    // One padding packet is enough.
    // So add a padding packet that will fill the rest of the segment
    padding_size = static_cast<uint16_t>(remaining_segment_space - NT_DESCR_DYN3_LENGTH);
  }
  else {
    // Exactly two packets are needed.
    // So add a padding packet so that the remaining space in segment matches a minimum packet
    padding_size = static_cast<uint16_t>(remaining_segment_space - (NT_DESCR_DYN3_LENGTH + min_padding_size));
  }

  // Setup DYN3 descriptor.
  NT_NET_SET_PKT_CLEAR_DESCR_DYN3(&buffer);
  NT_NET_SET_PKT_DESCR_TYPE_DYN3(&buffer);
  NT_NET_SET_PKT_CAP_LENGTH_NOALIGN(&buffer, padding_size);
  NT_NET_UPDATE_PKT_L2_PTR(&buffer);

  // Set the TX ignore bit to 1, such that the padding packet will not be transmitted.
  auto packet_ptr = NT_NET_GET_PKT_DESCR_PTR_DYN3(&buffer);
  reinterpret_cast<Dyn3_checksum_overlay*>(packet_ptr)->tx_ignore = 1;

  return NT_DESCR_DYN3_LENGTH + padding_size;
}

/**
 * Use the NT info stream to get the maximum size of a TX packet.
 */
static uint64_t get_max_packet_size(uint8_t port)
{
  int status;
  NtInfoStream_t info_stream;
  NtInfo_t info;

  // Open info stream.
  status = NT_InfoOpen(&info_stream, "transmit_segment_dyn_descr_example_info");
  handle_error_status(status, "NT_InfoOpen() failed");

  // Read NT info for a specific port.
  info.cmd = NT_INFO_CMD_READ_PORT_V9;
  info.u.port_v9.portNo = port;
  status = NT_InfoRead(info_stream, &info);
  handle_error_status(status, "NT_InfoRead() failed");

  // Close info steam.
  status = NT_InfoClose(info_stream);
  handle_error_status(status, "NT_InfoClose() failed");

  return info.u.port_v9.data.capabilities.maxTxPktSize;
}

int main(int, char**)
{
  // Note: Segments can be much larger than 8192 bytes, but this value gives
  // some nice printable results.
  constexpr uint64_t fcs_size = 4;
  constexpr uint64_t min_packet_size = 64;
  constexpr uint64_t segment_size = 8192;
  constexpr uint64_t total_packets = 100;
  constexpr uint8_t tx_port = 0;

  int             status;
  NtNetBuf_t      net_buffer_segment;
  NtNetStreamTx_t net_tx_stream;
  NtNetTxAttr_t   attr;

  // Initialize NT API.
  status = NT_Init(NTAPI_VERSION);
  handle_error_status(status, "NT_Init() failed");

  // Get maximum size of a TX packet for a specific port.
  uint64_t max_packet_size = get_max_packet_size(tx_port);

  // Initialize TX attributes struct and set up relevant stream related attributes.
  NT_NetTxOpenAttrInit(&attr);
  NT_NetTxOpenAttrSetName(&attr, "Checksum example NetTx");
  NT_NetTxOpenAttrSetPortMask(&attr, 1 << tx_port);

  // Set the TX packet descriptor to DYN3.
  status = NT_NetTxOpenAttrSetDescriptorMode(&attr, NT_NETTX_DESCRIPTOR_MODE_DYN3);
  handle_error_status(status, "NT_NetTxOpenAttrSetDescriptorMode() failed");

  // To tell the adapter where to look for the TX ignore bit.
  // 28 is the bit position of Dyn3_checksum_overlay.tx_ignore.
  status = NT_NetTxOpenAttrSetDescriptorPosIgnoreBit(&attr, true, 28);
  handle_error_status(status, "NT_NetTxOpenAttrSetDescriptorPosFrameType() failed");

  // While this example uses DYN3 descriptors, it does not use the "wireLength"
  // field to tell the FPGA the size of the packet, as is the default behavior,
  // but rather the "capLength" field.
  status = NT_NetTxOpenAttrSetDescriptorUseWireLength(&attr, false);
  handle_error_status(status, "NT_NetTxOpenAttrSetDescriptorUseWireLength() failed");

  // Open TX stream with attributes
  status = NT_NetTxOpen_Attr(&net_tx_stream, &attr);
  handle_error_status(status, "NT_NetTxOpen() failed");

  for (uint64_t packet_count = 0; packet_count < total_packets;) {
    // Use the option NT_NETTX_SEGMENT_OPTION_RAW to get a net buffer segment.
    status = NT_NetTxGet(net_tx_stream, &net_buffer_segment, tx_port, segment_size, NT_NETTX_SEGMENT_OPTION_RAW, 100);
    handle_error_status(status, "NT_NetTxGet() failed");

    // Create a new net buffer to use as a window into the segment net buffer.
    struct NtNetBuf_s net_buffer_packet;
    _nt_net_build_pkt_netbuf(net_buffer_segment, &net_buffer_packet);
    uint64_t remaining_segment_space = NT_NET_GET_SEGMENT_LENGTH(net_buffer_segment);

    // Fill the segment.
    while (remaining_segment_space > 0) {
      // Since segments has to be completely filled with packets, a check is needed
      // to prevent a case where the remaining segment space is too small to
      // contain a padding packet.
      uint64_t min_required_segment_space = NT_DESCR_DYN3_LENGTH + sizeof(Test_packet) + fcs_size +
        NT_DESCR_DYN3_LENGTH + min_packet_size;

      if (packet_count < total_packets && remaining_segment_space >= min_required_segment_space) {
        // Setup packet with a DYN3 descriptor.
        // Note: This also sets the tx_ignore to 0.
        NT_NET_SET_PKT_CLEAR_DESCR_DYN3(&net_buffer_packet);
        NT_NET_SET_PKT_DESCR_TYPE_DYN3(&net_buffer_packet);
        NT_NET_SET_PKT_CAP_LENGTH_NOALIGN(&net_buffer_packet, sizeof(Test_packet) + fcs_size);
        NT_NET_UPDATE_PKT_L2_PTR(&net_buffer_packet);

        // Copy packet data into TX net buffer.
        uint8_t* l2_ptr = reinterpret_cast<uint8_t*>(NT_NET_GET_PKT_L2_PTR(&net_buffer_packet));
        std::memcpy(l2_ptr, Test_packet, sizeof(Test_packet));

        packet_count += 1;

        std::cout << "Adding packet number: " << packet_count << std::endl;
      }
      else {
        // Copy a padding packet into net buffer.
        uint64_t padding_size = create_padding_packet_dyn3(net_buffer_packet,
                                                           max_packet_size,
                                                           remaining_segment_space);


        std::cout << "Adding padding packet with size: " << padding_size << std::endl;
      }

      // Get the next packet of the segment.
      remaining_segment_space = _nt_net_get_next_packet(net_buffer_segment,
                                                        NT_NET_GET_SEGMENT_LENGTH(net_buffer_segment),
                                                        &net_buffer_packet);
    }

    // Release / transmit net buffer segment from NT_NetTxGet
    status = NT_NetTxRelease(net_tx_stream, net_buffer_segment);
    handle_error_status(status, "NT_NetTxRelease() failed");
  }

  // Close TX stream, and then the NT API.
  status = NT_NetTxClose(net_tx_stream);
  handle_error_status(status, "NT_NetTxClose() failed");

  NT_Done();

  return 0;
}