I use a Microchip KSZ9031RNX as Ethernet phy on a custom board. I have two boards of the same type. The KSZ9031RNX is connected to an TI Sitara AM5728 (ARM Cortex A15) microcontroller that runs embedded linux (Kernel Version 4.19.38). Now I'am facing the problem, that the phy sporadically doesn't work as expected.
For example on board one the Link LED is always on. Regardless of whether an Ethernet cable is plugged in or not. And it is impossible to get an Ethernet connection. The chip seems not working. On the second board the link LED switches on when plugging in a cable and the board connects to the Ethernet as expected. But sometimes after powering off and on the phy doesn't work. The LEDs stay off when plugging in the Ethernet cable and an Ethernet connection can not be established. After one or some more power on resets the chip works without any fault again.
I checked the hardware several times and couldn't find any faults. So I'm going to exclude the hardware for now.
After powering on an additional reset is performed by pulling down the phy's reset pin for a few milliseconds. So afterwards the phy should be in an well defined state.
The reset circuit looks like this.
What I'm doing wrong?
Are there probably some special timing requirements at power on? Or a special power on sequence that has to be satisfied?
Are there some special timing requirements at power on? Or a special power on sequence that has to be satisfied?