Ethernet

The Fast Ethernet Controller (FEC) driver performs the full set of IEEE 802.3/Ethernet CSMA/CD media access control and channel interface functions. The FEC requires an external interface adapter and transceiver function to complete the interface to the Ethernet media. It supports half- or full-duplex operation on 10Mbps, 100Mbps, and 1000Mbps Ethernet networks.

The FEC driver supports the following features:

Half- and full-duplex operation
Link status change detection
Auto-negotiation (determines the network speed and half- or full-duplex operation)
Transmission of features such as automatic retransmission on collision and CRC generation
Statistics collection, such as transmit collisions, from the device

You can access the network adapter through the ifconfig command. The driver auto-probes the external adapter (PHY device).

Kernel configuration

You can manage Ethernet driver support through the kernel configuration option FEC Ethernet controller (CONFIG_FEC). This option is enabled as built-in on the default ConnectCore 6 SBC kernel configuration file.

Platform driver mapping

The Ethernet driver for the ConnectCore 6 system-on-module is located at drivers/net/ethernet/freescale/fec_main.c.

Device tree bindings and customization

The i.MX6 Ethernet interface device tree binding is documented at Documentation/devicetree/bindings/net/fsl-fec.txt.

The FEC interface is defined in the i.MX6 CPU, ConnectCore 6 system-on-module, and ConnectCore 6 SBC device tree files.

Definition of the FEC

Common i.MX6 device tree

fec: ethernet@02188000 {
    compatible = "fsl,imx6q-fec";
    reg = <0x02188000 0x4000>;
    interrupts-extended =
            <&intc 0 118 IRQ_TYPE_LEVEL_HIGH>,
            <&intc 0 119 IRQ_TYPE_LEVEL_HIGH>;
    clocks = <&clks IMX6QDL_CLK_ENET>,
             <&clks IMX6QDL_CLK_ENET>,
             <&clks IMX6QDL_CLK_ENET_REF>;
    clock-names = "ipg", "ahb", "ptp";
    status = "disabled";
};

IOMUX configuration

ConnectCore 6 system-on-module device tree

enet {
        pinctrl_enet: enet {
            fsl,pins = <
                MX6QDL_PAD_ENET_MDIO__ENET_MDIO       0x1b0b0
                MX6QDL_PAD_ENET_MDC__ENET_MDC         0x1b0b0
                MX6QDL_PAD_RGMII_TXC__RGMII_TXC       0x1b0b0
                MX6QDL_PAD_RGMII_TD0__RGMII_TD0       0x1b0b0
                MX6QDL_PAD_RGMII_TD1__RGMII_TD1       0x1b0b0
                MX6QDL_PAD_RGMII_TD2__RGMII_TD2       0x1b0b0
                MX6QDL_PAD_RGMII_TD3__RGMII_TD3       0x1b0b0
                MX6QDL_PAD_RGMII_TX_CTL__RGMII_TX_CTL 0x1b0b0
                MX6QDL_PAD_ENET_REF_CLK__ENET_TX_CLK  0x1b0b0
                MX6QDL_PAD_RGMII_RXC__RGMII_RXC       0x1b0b0
                MX6QDL_PAD_RGMII_RD0__RGMII_RD0       0x1b0b0
                MX6QDL_PAD_RGMII_RD1__RGMII_RD1       0x1b0b0
                MX6QDL_PAD_RGMII_RD2__RGMII_RD2       0x1b0b0
                MX6QDL_PAD_RGMII_RD3__RGMII_RD3       0x1b0b0
                MX6QDL_PAD_RGMII_RX_CTL__RGMII_RX_CTL 0x1b0b0
                MX6QDL_PAD_ENET_REF_CLK__ENET_TX_CLK  0x1b0b0
                MX6QDL_PAD_ENET_TX_EN__GPIO1_IO28     0x1b0b0
                MX6QDL_PAD_ENET_CRS_DV__GPIO1_IO25    0x1b0b0
            >;
    };
};

Ethernet enabling and PHY parameters

ConnectCore 6 SBC device tree

&fec {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_enet>;
    phy-mode = "rgmii";
    phy-reset-gpios = <&gpio1 25 2>;
    phy-reset-duration = <10>;
    phy-reset-wait = <1>;
    phy-supply = <&ldo4>;
    status = "okay";
};

MAC address

The MAC address of the i.MX6 Ethernet interface is programmed at the U-Boot environment (variable ethaddr) on the ConnectCore 6 eMMC. It is also printed on the module label.

U-Boot writes the MAC address in the ethaddr environment variable into the DeviceTree fec node under the local-mac-address property.

Known issues

The NXP i.MX6 CPU has a documented errata ERR004512 whereby the maximum performance of the Gigabit FEC is limited to 400Mbps (total for Tx and Rx).
The Micrel PHY KSZ9031 on the SBC carrier board may take between five and six seconds to auto-negotiate with Gigabit switches. To avoid this long delay during boot, the variable $bootscript is undefined by default and the auto bootscript feature does not run. To speed up the PHY's auto-negotiation, you can:
- Use a 10/100 switch (not Gigabit).
- Force the Micrel PHY to work as master during master/slave negotiation by setting the $phy_mode variable to master

Ethernet user space usage

In the Linux system, the Ethernet interface is known as ethX where X is a number, starting at 0, that indicates the interface index.

The Ethernet (FEC) driver exposes device data through the sysfs at /sys/class/net/ethX.

You can configure the Ethernet settings (IP, netmask, and so on) using the configuration file /etc/network/interfaces. You can manually configure and bring the interface up/down using the ifconfig program.