LP-AM261: Phy on fixed speed need seconds to establish a link

Hi Tobias,

Tobias Mader said:

For some applications it is necessary to send the first ethernet message under 500ms - reliable.

If you need fast startup time, my recommendation would be to bootstrap the PHY configuration for faster phy link up time. Are you already using that?

Meanwhile let me check the issue you described with LP internally. 

Hi Nilabh,

at the moment we're not using bootstrap for the phy configuration.

Hi Tobias,

How are you measuring the link up speed?

At the first step – visual (link led). Because I took seconds, in the worst case, the link led on the Phys showing that they have established link. If the Phys show good behavior, constantly showing directly a link, we will measure the rest with an oscilloscope.

Hi Tobias,

You can force the configuration in Ethernet IP example from the example project source file:

ind_comms_sdk_am261x_10_00_01_01/examples/industrial_comms/ethernetip_adapter_demo/device_profiles/common/device_profile_reset.c

You can make autoneg =0 and select 100M to 1 and check once if that meets the timing requirement.

Hi Nilabh,

Sry, we tested it, and it solves unfortunately not the problem. The fix would only be for the startup behavior?

The configuration should also be adoptable at runtime otherwise, we must restart the device every time we set a new phy speed.

Hi Tobias,

Tobias Mader said:

At the first step – visual (link led). Because I took seconds, in the worst case, the link led on the Phys showing that they have established link. If the Phys show good behavior, constantly showing directly a link, we will measure the rest with an oscilloscope.

My suggestion is that not to relay on the led blink and visual cue. As per phy datasheet the link up timings are:

I would suggest to use a oscilloscope or relevant tool for measuring the link up timings.

Also please refer to this on further details on measurement: www.ti.com/.../snla423.pdf

Hi Nilabh,

it looks like the application is dependent on BMSR, Link Status Register. This controls the ACD application and it only sends ARP messages as soon as there is a link. This is reproducible with us. This means that especially in the worst case, where it takes seconds to receive a link, the ACD application only starts sending its messages as soon as the Link LED turns on. The application itself comes from TI and also the drivers for this reason TI has the best insight to determine this.

Can you verify if we can rely on the datasheets here, if this is a software bug or the hardware?

Then we would have to think about which phy we can use.

HI Tobias,

What is partner(PC to which DUT is connected) link speed is it autonegotiation or forced.

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1276226/faq-can-auto-negotiation-link-up-with-force-mode-on-100mbps

Could you please once try with fixed on the partner side

Hi Nilabh,

that’s the case where it happens. Partner Device is fixed, e.g. 10Mbit/s full duplex and the LP-AM261 set to the same speed and duplex.

If both are auto negotiation everything is fine. And if the partner has auto negotiation enabled and the LP-AM261 has a fixed speed it works as expected. Only in fixed – fixed setup we got that problem.

Hi Tobias,

We are currently discussing this with our internal team to root cause the issue.

Hi Nilabh, 

now some time has passed. Any news?

Hi Tobias,

We are trying to debug the issue on our end and also we have initiated discussions with PHY team to understand the problem better.