DP83869EVM: DP83869EVM reproducible interoperability issue with Starlink Ethernet adapter (Idle Errors and RX Errors)

Hi,

I am investigating a Gigabit Ethernet interoperability issue between a Starlink Ethernet interface and the DP83869.

Initially this was observed on a custom media converter design using two DP83869 PHYs. To eliminate hardware-specific causes, I have now reproduced the same behaviour on a DP83869EVM.

Configuration

Topology:

The EVM is configured such that:

With this configuration the Starlink link comes up successfully.

Relevant registers after link establishment:

The PHY negotiates:

Problem Description

When connected directly to Starlink:

Download performance is significantly degraded.

Upload performance is much less affected.

While running a download speed test, the PHY accumulates large numbers of receive errors.

Idle Error Counter

Before speed test:

After speed test:

The idle error counter saturates at 255.

RX Error Counter

Before speed test:

After speed test:

RX errors increase substantially during download traffic.

Switch Insertion Test

When an unmanaged Gigabit switch is inserted:

The issue disappears completely.

Before Speed Test

After Speed Test

Results:

Additional Information

The same behaviour was originally observed on custom hardware using DP83869 PHYs.

The issue is therefore reproducible on:

and disappears when the immediate link partner is changed from:

to

Question

Have there been any known DP83869 interoperability issues involving:

or are there any recommended debug registers, DSP diagnostics, or workaround settings that could help identify why the PHY accumulates large RX and idle error counts only when directly connected to the Starlink Ethernet interface?

Thanks.