Using and testing the ports in Linux

This page applies to both Linux flows (PetaLinux and Yocto). It shows how to identify the Ethernet FMC Max ports, bring them up, check the link, and measure throughput against a PC. The commands are shown for the Yocto image, which logs in as the non-root amd-edf user and therefore uses sudo; in PetaLinux the same commands work (drop sudo when logged in as root).

What you need

The board booted into Linux with the Ethernet FMC Max fitted (see PetaLinux or Yocto).
A UART terminal on the board’s USB-UART (115200 baud, 8N1).
One or more Ethernet cables from the FMC ports to a PC with a Gigabit Ethernet NIC, or to a switch/router on the same network as the PC.
iperf3 on the PC (sudo apt install iperf3 on Ubuntu/Debian; Windows builds are available from the iperf3 project). iperf3, ethtool and phytool are already in the board images.

Identify the ports

Linux renames the network interfaces to predictable endN names early in boot (renamed from ethN in the kernel log). The N is assigned in probe order and does not follow the FMC port number, and it differs between targets and between the PetaLinux and Yocto images. The reliable way to identify a port is its MAC address, its controller base address, or its PHY address in the kernel log:

ip -br link
dmesg | grep -E "axienet|macb" | grep -E "renamed|PHY \["

Ethernet FMC Max port	MAC address	PHY in the kernel log
Port 0	`00:0a:35:00:01:22`	`axienet-<base>:01`
Port 1	`00:0a:35:00:01:23`	`axienet-<base>:03`
Port 2	`00:0a:35:00:01:24`	`axienet-<base>:0c`
Port 3	`00:0a:35:00:01:25`	`axienet-<base>:0f`

<base> is the address of axi_ethernet_0, because all four PHYs sit on its MDIO bus. The board’s own RJ45 (a PS GEM, driver macb) also appears in the list.

Example from the Yocto image on a ZCU106 (zcu106_hpc0), cables on FMC ports 0 and 3 and on the board’s RJ45:

$ ip -br link | grep ^e
end4             UP             00:0a:35:06:21:07 <BROADCAST,MULTICAST,UP,LOWER_UP>
end3             UP             00:0a:35:00:01:22 <BROADCAST,MULTICAST,UP,LOWER_UP>
end0             DOWN           00:0a:35:00:01:23 <NO-CARRIER,BROADCAST,MULTICAST,UP>
end1             DOWN           00:0a:35:00:01:24 <NO-CARRIER,BROADCAST,MULTICAST,UP>
end2             UP             00:0a:35:00:01:25 <BROADCAST,MULTICAST,UP,LOWER_UP>
$ dmesg | grep "PHY \["
macb ff0e0000.ethernet end4: PHY [ff0e0000.ethernet-ffffffff:0c] driver [TI DP83867] (irq=POLL)
xilinx_axienet a0000000.ethernet end3: PHY [axienet-a0000000:01] driver [TI DP83867] (irq=POLL)
xilinx_axienet a0080000.ethernet end0: PHY [axienet-a0000000:03] driver [TI DP83867] (irq=POLL)
xilinx_axienet a00c0000.ethernet end1: PHY [axienet-a0000000:0c] driver [TI DP83867] (irq=POLL)
xilinx_axienet a0100000.ethernet end2: PHY [axienet-a0000000:0f] driver [TI DP83867] (irq=POLL)

With the Yocto images the four-port Zynq UltraScale+ targets (ZCU102 HPC0/HPC1, ZCU106) come up with this mapping:

Interface	Device
`end3`	Ethernet FMC Max port 0 (`a0000000`)
`end0`	Ethernet FMC Max port 1 (`a0080000`)
`end1`	Ethernet FMC Max port 2 (`a00c0000`)
`end2`	Ethernet FMC Max port 3 (`a0100000`)
`end4`	Board RJ45 (PS GEM3, `ff0e0000`)

and on the ZCU104 (one FMC port) end0 is FMC port 0 and end1 is the board RJ45. For the PetaLinux mapping see Port configurations. On other targets, use the commands above.

Bring a port up

DHCP

In the Yocto image every Ethernet interface is managed by systemd-networkd and requests a DHCP address as soon as it has a link: plug the cable into a network with a DHCP server and the address appears in ip -br addr. In PetaLinux, request an address by hand:

sudo udhcpc -i end3

Static IP address

For a direct cable to a PC (no DHCP server), give the board port and the PC NIC addresses on the same subnet, for example board 192.168.10.10/24, PC 192.168.10.1/24:

sudo ip link set end3 up
sudo ip addr add 192.168.10.10/24 dev end3
ip -br addr show end3

If you use several ports at the same time, see Multiple ports on one network below.

Check the link

ethtool shows the negotiated speed and the link state:

$ sudo ethtool end3 | grep -E 'Speed|Duplex|Auto-negotiation|Link detected'
	Speed: 1000Mb/s
	Duplex: Full
	Auto-negotiation: on
	Link detected: yes

The kernel also logs every link change:

xilinx_axienet a0000000.ethernet end3: Link is Up - 1Gbps/Full - flow control off

phytool reads the PHY registers directly over MDIO. Pass the interface name and the PHY’s MDIO address (1, 3, 12 or 15 for ports 0 to 3); for example, to decode the IEEE registers of the port 0 PHY:

sudo phytool print end3/1

Speed negotiation

The DP83867 PHYs and the tri-mode MACs support 10, 100 and 1000 Mb/s, full and half duplex, and negotiate the speed with the link partner automatically (the AXI Ethernet core follows the speed the PHY reports over SGMII). To test a lower speed, restrict what the port advertises and let it re-negotiate:

sudo ethtool -s end3 speed 100 duplex full autoneg on    # advertise 100 Mb/s only
sudo ethtool end3 | grep Speed
sudo ethtool -s end3 speed 1000 duplex full autoneg on   # back to 1 Gb/s

The link partner must support the speed you select; the result is visible in the Link is Up kernel message and in ethtool.

Ping

ping -c 5 -I end3 192.168.10.1

-I makes the ping leave through that interface, which matters when several ports are up.

Throughput with iperf3

Start an iperf3 server on the PC:

iperf3 -s

Then, on the board, run a 10 second test in each direction through the port under test (--bind-dev forces the traffic through that interface):

iperf3 -c <pc-ip> --bind-dev end3 -t 10        # board transmits
iperf3 -c <pc-ip> --bind-dev end3 -t 10 -R     # board receives

The relevant figure is the receiver line at the end of each run. The table below lists results measured with the Yocto images: one TCP stream, MTU 1500, link partner a PC with a Gigabit Ethernet NIC.

Target	Port	Board transmits (Mbit/s)	Board receives (Mbit/s)
`zcu102_hpc0`	FMC port 0	941	886
`zcu102_hpc0`	FMC port 3	941	919
`zcu102_hpc1`	FMC port 0	941	934
`zcu102_hpc1`	FMC port 3	941	923
`zcu104`	FMC port 0	941	851
`zcu106_hpc0`	FMC port 0	941	914
`zcu106_hpc0`	FMC port 3	941	864
all of these	Board RJ45 (PS GEM3)	941	934

941 Mbit/s is the maximum TCP throughput of Gigabit Ethernet at MTU 1500, so transmit runs at line rate. The receive figure varies more from board to board and run to run; expect roughly 850 to 935 Mbit/s for a single stream. Pings showed no packet loss on any port. Lower results usually come from the PC side (NIC, power saving, other traffic) or from a link that negotiated below 1 Gb/s.

Multiple ports on one network

When two or more ports are connected to the same subnet, Linux may answer ARP requests and send replies through whichever interface it prefers, so traffic does not necessarily use the port you intend. Either:

bind each test to its interface (ping -I endN, iperf3 --bind-dev endN) and check the per-interface counters (ip -s link show endN) to confirm the traffic went through the port; or
give each port its own subnet, e.g. end3 = 192.168.1.10/24, end0 = 192.168.2.10/24, end1 = 192.168.3.10/24, end2 = 192.168.4.10/24, with a matching PC NIC on each.

If a port does not work

See Troubleshooting.