How does STM32F429ZI MAC controller know when Collision occurs?

[LLOLO.1]

Hi I am currently working on a project where I have to implement TCP/IP stack on STM32F429ZI 144 pin nucleo board. Board has PHY chip.My question is how does the MAC controller knows when a jabber or collision event occurs since these events are handled by PHY chip. PHY chip shown in schematic for nucleo board, has no connections other than RMII (like error interrupt?) to STM32 MCU.

[Pavel A.]

"The missing COL signal is derived from AND-ing together the TX_EN and the decoded CRS signal from the CRS_DV line in half duplex mode. " Wikipedia