MAC_RXFIFO_SIZE
hwm = max(MAC_RXFIFO_SIZE - 3 * mtu, (MAC_RXFIFO_SIZE * 38) / 100);
return min(hwm, MAC_RXFIFO_SIZE - 8192);
lwm = min(3 * (int) mtu, MAC_RXFIFO_SIZE /4);
pause_bits = MAC_RXFIFO_SIZE * 4 * 8;