Clarification on Ethernet Switch Configuration for STM32MP257-based Design

[asadullah4571]

Hi ST Team, 

First of all, I would like to thank you for your support on my previous project based on the STM32MP255D series, which has now successfully moved into production.

First of all, I would like to thank you for your support on my previous project based on the STM32MP255D series, which has now successfully moved into production.

Currently, I am working on a new project that is entirely focused on Ethernet-based communication. Below is my design requirement and a clarification request:

Project Requirement

• The system requires three Ethernet interfaces in total:

  1. Ethernet 1: Operates in standalone mode (independent network).

  2. Ethernet 2 and Ethernet 3: Should function as switch ports, supporting STP (Spanning Tree Protocol) for loop prevention.

Network Topology and Data Flow

• Ethernet 1 is used for independent communication (standalone).

• Ethernet 2 connects to Device A, which is daisy-chained to Device B.

• The last device (Device B) connects back to Ethernet 3, forming a potential loop in the same network domain. can i send some data from Ethernet 2/3 to devices

In this setup, I expect that when the loop is detected, STP should automatically block one of the switch ports (either Ethernet 2 or Ethernet 3) to prevent network looping.

Clarification Needed

1. On the STM32MP257-EV1 board, which has three Ethernet ports, can Ethernet 2 and Ethernet 3 operate simultaneously in switch configuration mode while Ethernet 1 remains standalone?

2. When the switch configuration is enabled, how can application-level data be transmitted through Ethernet (e.g., sending or receiving packets to/from devices connected via the switch ports)? Should the traffic be handled via the CPU Ethernet interface or directly through the switch fabric?

Your guidance on configuring and managing this Ethernet switch setup — especially with respect to STP functionality and application data routing — will be greatly appreciated.

[Erwan SZYMANSKI]

Hello @asadullah4571 ,

In fact, ETH2 is the standalone interface while ETH1 and ETH3 are both connected to the HW switch. I think you will have a better picture following the wiki article below about how all of this work:

• https://wiki.st.com/stm32mpu/wiki/X-LINUX-TSNSWCH_expansion_package
• https://wiki.st.com/stm32mpu/wiki/How_to_configure_Ethernet_switch

So yes, with ETH1 and ETH3, your use case of having a kind of Ethernet ring topology in daisy chain will work. By default, with the configuration provided by ST (configuration scripts in the X-LINUX-TSNSWCH expansion package), the STP is activated by default, so according to the protocol, if it detects a loop somewhere, it will cut one port to keep a single Ethernet path to an endpoint.

In the article, you will also see that to communicate from the SoC to the switch on MP2 point of view, we mount a new Ethernet interface (called sw0ep in the article and scripts) that is the interface used to communicate on switch network.

I hope it clarifies a bit your questions, if not do not hesitate to ping me back.

Kind regards,
Erwan. 

[asadullah4571]

@Erwan SZYMANSKI 

Thanks for the Quick clarification,
One more thing I need to be clarification, that if I will  try to communicate between the device to device, means 

from  device X which is connected to  ETH2 standalone  -------- >  ETH3 /ETH1 (switch )  to device A/B/C  is it possible? means IP_Forwarding  In between standalone and switch.

because i do not have EV1 Board , once you clarified i will make the custom board of stm32mp257.

[Erwan SZYMANSKI · Accepted solution]

Hello @asadullah4571 ,
Yes you can forward traffic from standalone port to switch port by making some configuration. This wiki article will help you to go forward on this point: https://wiki.st.com/stm32mpu/wiki/How_to_create_a_bridge_between_ETH1,_ETH2,_ETH3

Kind regards,
Erwan.