Verdin Module Onboard Ethernet Activity is on when there is no link

We are using Verdin IMX8MM V1.1B on a Verdin Development board.

The LEDs for Verdin integrated Ethernet show a strange behavior.
There is one LED (seems to be ACT) which is perpanently on when there is NO cable attached. When the cable is attached, it starts blinking.

Because we copied the schematic of the verdin development board to our custom carrier board, we have the same behavior there and this is a problem.
Is this a known issue? What is the reason? How to make this LED dark when there is no link?

Ok, as I got not answer, we worked around the problem. We’ll have only one LED visible in our housing (LED2). We modified the micrel phy driver drivers/net/phy/micrel.c
In kszphy_config_reset , add at the end:

	phy_write(phydev, 0x16, 0x0E);  /* LED1 off, LED2=combined Link/Act */
	phy_write(phydev, 0x17, 0x8000); /* enable enhanced LED mode with Bit 15 (undocumented bit!) */
	phy_write(phydev, 0x1a, 0x00); /* enabled enhanced LED mode */

Hello Klausci,

This is a known issue with the microchip phy.
The default behavior is that one of the LEDs is lit up when in reset mode and even no cable plugged in. This should not be as by the description of the KSZ9131 datasheet. By default this PHY is in an “KSZ9031-LED-Mode” which simply does not work. Asking Microchip about it they said:

Set Register 30d, bit 9 = 1, and indeed after setting this bit it works. It is not documented yet so one could make a proper workaround in the driver that also checks the chip-version and it is unclear if they will fix it in the silicon or not.
You have to set the register here.
reg 30d, bit9 = 1

Best Regards,

Matthias Gohlke

Got it. It would be very helpful if Toradex could provide a list of known errata for each product. Or is it already available?

Hello Klausi,

yes we have the Erratas on this site here: Verdin iMX8M Mini | Toradex Developer Center
But in your case you are right it should be there more explicit under HAR-3184
I forwarded that to the Product management.

Best Regards,


Hello Matthias, thanks for the Errata link. However. I can’t see how HAR-3184 is related to the LED issue. HAR3184 is only affecting V1.0 modules, but we are using V1.1.

Hello, yes you are right. It is the KSZ9131 has the Problem. I already advised the Product management to create an Errata for this.

Best Regards,