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.
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;
}It provides ping capability. It is useful to check if the design is up when using standard network equipment such as, routers or NICs.
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 application communicates with this module using the S_AXIS_sk2nl and M_AXIS_nl2sk AXI4-Stream interfaces with the following structure:
struct my_axis_udp {
ap_uint<512> data;
ap_uint< 64> keep;
ap_uint<16> dest;
ap_uint< 1> last;
}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.
Currently to simplify the receiver side logic, valid incoming connections must be fully specified in the socket table.
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