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).

These options are enabled as built-in on the ConnectCore 6 Plus SBC kernel configuration file.

Kernel driver

The Ethernet driver for the ConnectCore 6 Plus 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 Plus, and ConnectCore 6 Plus SBC device tree files.

Definition of the FEC

{cpu-family} device tree
fec: ethernet@2188000 {
	compatible = "fsl,imx6q-fec";
	reg = <0x02188000 0x4000>;
	interrupt-names = "int0", "pps";
	interrupts = <0 118 IRQ_TYPE_LEVEL_HIGH>,
	             <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";
	stop-mode = <&gpr 0x34 27>;
	fsl,wakeup_irq = <0>;
	status = "disabled";

IOMUX configuration

ConnectCore 6 Plus SBC 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_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_ENET_TX_EN__GPIO1_IO28     0x1b0b0
			MX6QDL_PAD_ENET_CRS_DV__GPIO1_IO25    0x1b0b0

Ethernet enabling and PHY parameters

ConnectCore 6 Plus SBC device tree
&fec {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_enet>;
	phy-mode = "rgmii";
	phy-reset-gpios = <&gpio1 25 GPIO_ACTIVE_HIGH>;
	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 in the U-Boot environment (variable ethaddr) on the ConnectCore 6 Plus eMMC. It is also printed on the module label.

U-Boot writes the MAC address in the ethaddr environment variable into the fec device tree 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 U-Boot environment 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.