I see in the data sheet that the W5500 supports WOL and power down mode, but I have some questions about these functions. What state is power down mode? Is it the same as setting the PHYCFGR register to power down mode?
From what state does WOL wake the chip? How do I enter this state?
It looks to me like if I enter PHY power down mode, I can not receive the magic packet via UDP. What I want to do is sleep my device/enter low energy mode until I receive a wakeup request from my application sending the WOL packet.
Reading datasheet I would say these are two separate features:
wake on LAN’s purpose is to activate interrupt pin, and this event is expected to wake the MCU up. Of course W5500 should have PHY up and running as you said;
power down mode is when you just turn PHY off (it is exhibited by chip cooling down and consumption current down from 132 mA to 13 mA). Of course, as you said, in this mode WOL will not work.
It is a question to your MCU manufacturer and MCU’s datasheet how it can be put into the power saving mode, and what “external world” should do to it in order to get it out of sleep. For WoL definition please refer here [url]https://en.wikipedia.org/wiki/Wake-on-LAN[/url].
