Gigabit PHY connectivity

[adamkf]

@tlalexander: Interesting project, following your progress with great interest. I in the process of coming up with something similar but in an ITX format.

Have you come up with a way to connect the gigabit PHY on the CM4 to the switch PHY? I noticed you are trying capacitive coupling (C1 thru C16). What value are you using here? 100nF? I'm curious if you've been able to test this or have datasheet references to back this decision up?

I've seen some designs mention you may need resistors if using current mode PHY's (see: https://resources.altium.com/p/gigabit-ethernet-101-basics-implementation, paragraph before figure 19), but not sure what the case is with the CM4 and switch IC's. Still digging into that.

[sequoia-hope]

The truth is I do not know for sure if the broadcom PHY is current mode or voltage mode. I am hoping for the best, but if you want to ask on the raspberry pi forum perhaps someone can give us the answer. I will look at your link - perhaps I could lay out some space for resistors if needed.

Glad you like the design!

[daveismith]

Did you ever get to a point where you built the design and validated the ethernet switch?

[sequoia-hope]

Sadly no this project fell by the wayside. The board is not even fully routed.