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Fixed-link SGMII degraded speed

Question asked by Dávid Huber on Dec 13, 2019

Hy NXP Team,


We are developing a complex system using two LS1046A processors. We are using QorIQ-SDK-V2.0-20160527. The two NXP is connected via SerDes interface. Each side is using the SerDes1 Lane C configured for SGMII connection with 1333 protocol in the RCW. This SerDes lane is connected with the fm1-mac10 interface. The device-tree binding also configures sgmii fixed-link connection:

ethernet@f2000 { /* 10GEC2 */
   phy-connection-type = "sgmii";
   fixed-link {
      speed = <1000>;


The ethtool fm1-mac10 log shows the following:


Settings for fm1-mac10:
Supported ports: [ MII ]
Supported link modes: 1000baseT/Full
Supported pause frame use: Symmetric Receive-only
Supports auto-negotiation: Yes
Supported FEC modes: Not reported
Advertised link modes: 1000baseT/Full
Advertised pause frame use: Symmetric Receive-only
Advertised auto-negotiation: Yes
Advertised FEC modes: Not reported
Link partner advertised link modes: 1000baseT/Full
Link partner advertised pause frame use: No
Link partner advertised auto-negotiation: No
Link partner advertised FEC modes: Not reported
Speed: 1000Mb/s
Duplex: Full
Port: MII
Transceiver: external
Auto-negotiation: on
Supports Wake-on: d
Wake-on: d
Current message level: 0xffffffff (-1)
drv probe link timer ifdown ifup rx_err tx_err tx_queued intr tx_done rx_status pktdata hw wol 0xffff8000
Link detected: yes


However, if I measure the link speed using iperf between the two fm1-mac10 interfaces of each side gives the following result:


Client connecting to, TCP port 5001
TCP window size: 45.0 KByte (default)
[  3] local port 49651 connected with port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  11.4 MBytes  9.53 Mbits/sec


I also tried to disable autonegotiation on both sides using ethtool, but this did not solve the problem.


We have investigated the SerDes link on our board with oscilloscope, and the eye diagram looks pretty.

We are using the similar fixed-link SGMII connections on the fm1-mac5,6 interface but connected to other processor types and it works perfectly.


Do you know about any limitation with fixed-link connection between two LS1046A processors?

Do you know any configuration which may solve our problem?