Add virtual Ethernet ports to single port MCUs

February 05, 2016 // By Graham Prophet
Segger’s TCP/IP stack now offers support for the “Tail Tagging” feature of Micrel/Microchip Ethernet switches. embOS/IP is the first embedded IP stack to support Tail Tagging.

This enhancement establishes multiple virtual Ethernet ports when only one physical Ethernet port is available on the CPU - by choosing another PHY.

Offering more than one Ethernet port is normally complex, difficult to handle, and most CPUs only have a single port Ethernet controller. It requires additional components such as external Ethernet controllers to extend the number of available ports.

Micrel/Microchip has developed switches which are able to expand one Ethernet port of the CPU into 1+n fully independent ports for the network by using the so-called Tail Tagging mode. Several ports might, for example, be needed when building a router where every port has to be addressed individually. Additionally, multiple ports can be used to create redundant networks, known as multihoming.

Port addressing is done on a pure software basis and is transparent to the outside. The new feature allows every port to have its own assigned MAC-address so that they appear like different physical hosts in a network.

Hardware to evaluate the feature takes the form of the embOS/IP Switch Board that includes an NXP Kinetis K66 CPU, Micrel/Microchip switch PHY KSZ8794CNX with three usable Ethernet ports and an on-board version of SEGGER’s popular J-Link debug probe. Tail Tagging support, together with a PHY driver, is available as an add-on. The package can be easily evaluated using SEGGER Embedded Studio, even while in evaluation mode.

More information on Tail Tagging support;

Segger’s embOS/IP Switch Board;