Implement GEMAC PHY driver, that initialize the PHY to prepare for Ethernet transfer.

Usage

1. EMAC related pins and Driver should be initialized at first.
2. Initialize GMACB Driver instance by invoking GMACB_Init().
3. Initialize PHY connected via GMACB_InitPhy(), PHY address is automatically adjusted by attempt to read.
4. Perform PHY auto negotiate through GMACB_AutoNegotiate(), so connection established.

Related files:
gmacb.h
gmacb.c
gmii.h.