DP83TG720R-Q1: PHY links down during performance test

Hi Jian,

• Can you explain in more detail about what is done in the RFC2889 performance test, such as the actions that are performed and the conditions? I have not heard of it before.
• Is this issue observed with other MAC partners besides the Realtek 9071CL?
• Are we certain that the link is really down, or is there just no data being transmitted? Does the PHY respond normally to register reads during the "link down" time?

Jian Liu said:

1.Could it caused by PHY internal protection during high forward rate test?

To my knowledge, the PHY doesn't have protection or recovery mechanisms related to data forwarding. It sounds more likely that this could be a signal quality issue or some other interruption of normal link communication.

Jian Liu said:

2.Is there any way to find the root cause by reading some status registers or other debug method?

This could be difficult if the link is only down for 1 second and comes up. If you are able to access the PHY registers, it may be helpful to check the value of register 0x0001 to see if the MDI link is really up or down during the "link down" time.

Best,

Evan Su

Hi Evan,

Thanks for your reply.

>Can you explain in more detail about what is done in the RFC2889 performance test, such as the actions that are performed and the conditions? I have not heard of it before.

For the detail information of RFC2889 performance test, you can refer to https://datatracker.ietf.org/doc/html/rfc2889#section-5.6.

Basically, it's used to verify the DUT's maximum forwarding rate without packet loss. So in our performance test, we are sending packets with 1000Mbps from upper tester to DUT.

>Is this issue observed with other MAC partners besides the Realtek 9071CL?

No. We only tested 720R PHY connected with Realtek 9071CL.

>Are we certain that the link is really down, or is there just no data being transmitted? Does the PHY respond normally to register reads during the "link down" time?

The link partner (upper tester )  shows the link down information in its log.

Currently, we have performed RFC2889 performance test around 3 times and observed this issue once. We will keep testing and feedback you.

If you have any idea, please feel free to tell us.

Thank you!

BRs

Liu Jian

Hi Jian,

OK, this is interesting. I am reviewing with my team but in the meantime I suggest you check the registers from the PHY if possible. Is there a way to halt the test when the link is down?

Best,

Evan Su

Hi Evan,

I think there is no way to halt the test when the link is down.

We performed test again yesterday but didn't observe this issue.

Maybe this issue is not caused by the PHY?

We will continue testing and feedback you in case this issue can be reproduced.

Thanks for your support!

BRs

Liu Jian