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This white paper is based on [[AN-BELK-006:_Enabling_dual_Gigabit_Ethernet_support_on_BoraEVB/BoraXEVB | AN-BELK-006]] and it describes shows how to access enable second Ethernet interface by the use of native GEM1 controller. That application note allows to support both ETH PHY on Bora SOM and BoraEVB through MDIO interfaces under U-bootEthernet ports in Linux. Some changes must In some circumstances, it can be made required to access second Ethernet port in U-boot sources in order to enable access to both GEM0 and GEM1 Zynq controllersBoot as well. For more details please contact TBD

The [[AN-BELK-006:_Enabling_dual_Gigabit_Ethernet_support_on_BoraEVB/BoraXEVB | AN-BELK-006]] gives access This white paper describes how to use both ethernet Ethernet ports only under in U-bootBoot. For some reasons the user may want It is worth remembering that '''default U-Boot delivered with Bora Embedded Linux Kit''' or '''BoraX Embedded Linux Kit does not support second Ethernet interface'''. A modified version is required to fully access run the net independently through both ETH connection even by the Uexamples presented here. For more information please contact [mailto:support-boot bootloaderbora@dave.eu technical support].

Below is the The following block diagram describing shows the ethernet phy's Ethernet native controllers/PHYs topology as implemented in the [[AN-BELK-006:_Enabling_dual_Gigabit_Ethernet_support_on_BoraEVB/BoraXEVB | AN-BELK-006]].* PHY #1 : is the ethernet Ethernet PHY on the Bora SOM* PHY #2 : is the ethernet Ethernet PHY on the BoraEVB* PHY #3 : is a dummy PHY implemented in the GMII-to-RGMII bridge IP. It has only one register to correctly set the RGMII bus frequency , based on ETH Ethernet link speed.

Following commands shows show how to initialize the second ethernet PHY Ethernet port in U-boot and to download a file via TFTP:. * at At first boot the second ethernet Ethernet interface is unable to find MAC address, so it must be set as an U-boot environment variable:

* To switch between the two ethernet Ethernet interfaces the user must be corretly set the ''<code>ethact'' </code> environment variable properly (this variable is reset to its default at every system reboot):** To to access GEM0 (Bora SOM ethernet phy) : <code>setenv ethact Gem.e000b000</code>** To to access GEM1 (BoraEVB ethernet phy) : <code>setenv ethact Gem.e000c000</code> If the user want to use the Bora SOM ethernet interface all accesses such as loading a file via TFTP are stright forward.

If the user want wants to use the Bora SOM Ethernet interface, regular network commands can be used.Instead, If the user wants to access the net LAN through the BoraEVB ethernet Ethernet interface, some init additional initialization commands must be issued, as detailed in the rest of the document. Below this steps are provided:

Issue After setting <code>ethact</code> variable to select second Ethernet port, issue a net access command like <code>ping</code>. This command is just used to init initialize the ethernet Ethernet PHY #2 and PHY #3 on the BoraEVB. The <code>ping </code> command fails because the GMII-to-RGMII bridge (PHY #3) is not yet fully initialized :

The two PHY #2 and PHY #3 are now partially initialized and, as such, can be listed and accessed via ''<code>mii'' </code> U-boot command:

The last steps implies to correctly configure step consists of configuring the GMII-to-RGMII bridge. This IP has an internal dummy (virtual) MDIO PHY at the ''<code>0x8'' </code> address. Is has only one internal register that is used to set ethernet Ethernet link speed and consequently the RGMII interface clock frequency. For more detail about the GMII-to-RGMII bridge IP and the internal register please refer to the [https://www.xilinx.com/support/documentation/ip_documentation/gmii_to_rgmii/v3_0/pg160-gmii-to-rgmii.pdf Product Guide].

Since the ethernet Ethernet PHY on BoraEVB is configured with auto-negotiation enabled by default, The user must know the link speed negotiated on this interface before setting the GMII-to-RGMII register.Following are Please use the command associated to the commands negotiated link speed:** link @ 10M 10Mbps : <code>mii write 0x08 0x10 0x0</code>** link @ 100M 100Mbps : <code>mii write 0x08 0x10 0x2000</code>** link @ 1000M 1000Mbps : <code>mii write 0x08 0x10 0x40</code>

After the user can access the net via the BoraEVB ethernetOnce virtual PHY #3 is fully initialiazed, second Ethernet port is finally available: