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Network layer kernel

The network layer kernel is a collection of HLS modules to provide basic network functionality. It exposes two 512-bit (with 16-bit TDEST) AXI4-Stream to the application, S_AXIS_sk2nl and M_AXIS_nl2sk.

ARP

It provides a translation between IP addresses and MAC addresses. This table has 256 elements and it is accessible using AXI4-Lite. It also has ARP discovery capability to map IP addresses on its subnetwork.

struct arpTableEntry {
  ap_uint<48> macAddress;
  ap_uint<32> ipAddress;
  ap_uint<1>  valid;
}

ICMP

It provides ping capability. It is useful to check if the design is up when using standard network equipment such as, routers or NICs.

UDP

It provides UDP transport layer functionality. It has a 16-element socket table, which must be filled from the host side in order to receive and send data.

struct socket_table {
  ap_uint<32>     theirIP;
  ap_uint<16>     theirPort;
  ap_uint<16>     myPort;
  ap_uint< 1>     valid;
}

The user application communicates with this module using the S_AXIS_sk2nl and M_AXIS_nl2sk AXI4-Stream interface.

In the transmitting side, the application sends the payload identifying the socket using dest. If the socket is valid, an UDP packet containing the payload is populated to the network. If the socket is not valid, the payload is dropped.

In the receiving side UDP packets are parsed and the socket information is compared against the socket table. If the socket information is valid, the UDP will populate the payload to the application setting dest accordingly, the user signal will also contains metadata pertaining to source and destination IP address as well as source and destination port.

Currently, to simplify the receiver side logic, valid incoming connections must be fully specified in the socket table.

The structure for these two interfaces are specified below.

User kernel to network layer (S_AXIS_sk2nl)

struct udp_app2nl {
  ap_uint<512>    data;
  ap_uint< 64>    keep;
  ap_uint< 16>    dest;
  ap_uint<  1>    last;
}

Network layer to user kernel (M_AXIS_nl2sk)

struct userMetadata {
    ap_uint<32>     myIP;
    ap_uint<32>     theirIP;
    ap_uint<16>     myPort;
    ap_uint<16>     theirPort;
};

struct udp_nl2app {
  ap_uint<512>    data;
  ap_uint< 64>    keep;
  ap_uint< 16>    dest;
  ap_uint<  1>    last;
  userMetadata    user;
}

Embedded Probes

The network layer contains embedded probes at different points in order to facilitate debug and monitorization. These probes provide the following metrics: a) number of packets, b) number of bytes and c) active time (number of cycles), suffices _packets, _bytes and _cycles respectively.

These metrics can can be clear by writing 0x1 to the register debug_reset_counters, be aware that this is global event and all probes are clear.

The NetworkLayer class in the vnx_util.py file provides the getDebugProbes property that returns a dictionary with the current value of the probes.

Below you can find the probes and their description. For more information about the offset address of each of them refer to the kernel.xml file.

Receiving Path

Name Description
eth_in Incoming packets from the Network interface
pkth_in Incoming packets after filtering
arp_in Incoming ARP packets
icmp_in Incoming ICMP packets
udp_in Incoming UDP packets
app_in Incoming UDP Segments to the application

Transmitting Path

Name Description
eth_out Outgoing packets to the Network interface
ethhi_out Outgoing packets after Ethernet header insertion
arp_out Outgoing ARP packets
icmp_out Outgoing ICMP packets
udp_out Outgoing UDP packets
app_out Outgoing UDP Segments from the application

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