Today I can say with confidence that my own writed Ethernet Gigabit code works fine. ARP and ICMP (ping) work perfect. DHCP will not be realised, the new firmware will work only with static IP.
Next step - create new bootloader that will be able to write firmware in 3 different slots and also write itself.
A programm on PC side will be writed on Python so Linux users will be able to use it easy.