Need ping before UDP transactions

[liubenyuan]

Hi, I finally get VNx works on ADM-PCIE-9V3, use the settings post in this issue #114 The solution is disabling the RS FEC. (Issue #114 can not be commented). The last paragraph in Ethernet folder says that RS FEC should be enabled manually via the AXI4Lite interface.

There is one problem. After writing the bitstream to FPGA and wait for link on, we do UDP test. But everytime, the first UDP transaction will not complete. It stucks at sock.recv. The solution is treaky. We burn the bitstream, and do a ping, for example, ping remote_ip. After that, the first transaction of UDP succeed.

Is it the normal behavior of VNx or 100G-fpga-network-core? How could I debug and solve this issue? I guess it must be that the ARP table are not established during first transaction of UDP, so it needs a ping to build the ARP table.

The following is the test code written in python.

import socket

remote_ip = "192.168.0.5"
remote_port = 8001
outgoing_if = "192.168.0.10"  # local ip interface
local_port = 8002

# BUG: need ping before the 1st UDP tx/rx
# delay = ping.do_one(remote_ip, 100)
# print(f"{delay=}")

message= "12345678" * 64

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind((outgoing_if, local_port))
sock.connect((remote_ip, remote_port))

# send and recv
sock.send(message.encode())
print(f"{message} to {remote_ip}:{remote_port}")
# data, addr = sock.recvfrom(8)
data = sock.recv(8)
print(f"received message: {data}")

[liubenyuan]

Hi, I read the notebook and XRT examples, do I need to manually build the ARP table via the AXI4 Lite interface before the first UDP transaction?

https://github.com/Xilinx/xup_vitis_network_example/blob/47063d88843254f3c4c587a85378c51d4bb14696/xrt_host_api/src/networklayer.cpp#L76

For example the ping_fpga.cpp demo in XRT writes: https://github.com/Xilinx/xup_vitis_network_example/blob/47063d88843254f3c4c587a85378c51d4bb14696/xrt_host_api/examples/ping_fpga/ping_fpga.cpp#L238

        networklayer.arp_discovery();
        std::this_thread::sleep_for(std::chrono::seconds(5));
        auto table = networklayer.read_arp_table(255);

Thanks again for this great project!