TSE MAC behavior when ethernet cable unplugged during operation

[TSchu3]

Hello, I am experiencing problems resuming transmission after the Ethernet cable has been unplugged and then plugged back in.
I am working with the TSE MAC in 10/100/1000 mode with RGMII interface to an external PHY. Quartus Version 22.1.1 on a Cyclone V.

The system works as expected during power up and stopping/ starting traffic etc.  However, if the cable is unplugged while transmitting data  I am unable to resume transmission after the cable is replaced.
The PHY indicates that the link is back up.
I can see that the FPGA facing side of the MAC is showing that transmit_ready is high, but ff_tx_septy is low. 

septy being low pauses the logic.  But I would expect the MAC to resume transmitting the packets already in its buffer which would then clear the septy signal,  but it does not and the mac will not resume transmission without a reset.

What is the expected behavior of the MAC when the PHY loses link mid transmission?
Should I be doing something different on the logic side if loss of link is detected?
Any other signal I should be looking at?

Thanks in advance!

[Paveetirra_Srie]

Hi,

By looking at the issue description,  it is possible that Ultra Low Power Mode (ULP) is causing the problem. ULP is part of Energy Efficient Ethernet. When ULP is enabled, the Ethernet controller may enter a low-power state that makes it less responsive to link changes or other events. This could explain why the link is not re-established when you remove and reinsert the cable.

To disable ULP, you may need to change the power management settings of the Ethernet adapter in Windows. You should be able to find these settings in the Device Manager, under the properties of the Ethernet adapter.

You may be able to disable ULP in the BIOS settings of your computer, if this option is available. Keep in mind that disabling ULP may increase power consumption and negate some of the power-saving benefits of Energy Efficient Ethernet. And you might check the whether the driver version is up to date.

https://www.intel.com/content/www/us/en/products/sku/82185/intel-ethernet-connection-i219lm/downloads.html

Kindly do let me know if it helps.

Regards,

Pavee

[TSchu3]

Pavee, thank you for responding.

The issue is not that the link will not come back up,  in fact it does come back up and very quickly.  I can observe this by monitoring a link status line from the external PHY. 
The issue I'm having is that once the link does come back up, the TSE MAC does not resume transmission.  Its buffers remain at the SEPTY level.  That level is used as an almost full for the TSE MAC internal buffers so when it is low (almost full) my internal logic can not send any data and is stalled.

So far the only way I have found to clear this condition is a reset.

I'm looking for more information of the expected behavior of the TSE MAC when link is lost mid-transmission.  And if there is something else I should be doing to get it to resume transmitting.

Thanks!

[Paveetirra_Srie]

Hi,

Good day to you.

Have you tried the Flow Control method? Here's the details on Flow Control:

https://www.intel.com/content/www/us/en/docs/programmable/683402/22-4-21-1-0/congestion-and-flow-control.html

Kindly do let me know if it helps.

Regards,

Pavee

[TSchu3]

Thank you for your response.  Can you please help me understand how flow control (i.e. pause frames) are related to the issue which involves unplugging the Ethernet cable and plugging it back in?

[Paveetirra_Srie]

Hi,

We do not receive any response from you to the previous reply/answer that I have provided. This thread will be transitioned to community support. 

If you have a new question, feel free to open a new thread to get the support from Intel experts. 

Otherwise, the community users will continue to help you on this thread. 

Thank you.