DP83867IR: Loopback test

Hi Taylor,

So I understand what is going on, you are doing an external loopback test using DP83867IR by using a loopback cable on MDI but only just after power-on at certain temperatures and goes away after some time, is this correct?

Some questions:

- How long is the cable?

- Is this present during room temperature condition?

- After what time does packet errors not get reported? Has the PHY linked up with itself when you are seeing packet errors, or could you be seeing it before linkup has occurred? 

Sincerely,

Gerome

Hi Gerome

The loopback test only fails at -40'C or 70'C ambient temp and only happens for the first few seconds, so to confirm when the PHY is ready to switch to loopback test mode so the test can start? Check registers or other methods?

Loopback like this picture, cable under 5cm.

Not present during room temperature.

Thanks 

Taylor

Hi Gerome,

After logging into Linux, I use the following command to set the Ethernet net speed to 100M and check its link status:

$ ethtool -s eth0 speed 100 duplex full autoneg off
$ cat /sys/class/net/eth0/operstate"

up

Once everything was in place, I performed an external loopback test using the socket read/write test in C. Randomly, in the first 2-3 reading and writing tests, the application could not receive data.

Thanks,

Sean

Hi all,

Wanted to double check. If you connect the PHY to another PHY with normal length cable (10m), do you still see these packet errors?

So you are sending the data from the MAC out to PHY, looping back externally to go back up to MAC? If you put PHY into digital loopback, do you still see these issues?

If its a timing issue, to ensure that you are not prematurely sending packets, could you send packets a minute after powerup? 

After first 2-3 readings are not present, you are saying that the next readings are clean?

Sincerely,

Gerome

Hi Gerome

Please follow our question, we just need to check the loopback mode ready register, or give us a delay time, thanks.

Taylor

Hi Taylor,

I am still trying to understand the problem statement fully to provide you the most accurate debug steps. 

If issue is only happening when PHY starts up at very high or low temperatures, is the problem not seen after those 2-3 reads? 

It may be possible that PHY is not linked up with itself yet and you are prematurely sending packets. Upon powerup, PHY may take multiple seconds to link up.

Sincerely,

Gerome

Hi Gerome

Yes, the problem was not seen after those 2-3 reads.

We've added a big timeout of 15 seconds, so we're wondering how to confirm when the PHY is link up?

Taylor