Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f2/STM32F215/Ethernet_MAC/MACMIIAR#0x0
Ethernet MAC MII address register
MII busy
MII write
Clock range
MII register
PHY address
https://github.com/modm-io/cmsis-svd-stm32