Ethernet doesn't work

My board(ns7520 cpu) use LXT971 as phy chip. I have debuged the bsp. the mii_reset() function return 0(ok) mii_identify_phy() return INTEL_PHY(ok) mii_negotitate() and mii_check_speed() return ok. But I can’t use ping to connect my board. Is there some problem in the transformer or some other chip wrong? How to debug this problem? Is there some document about the TX+¡¢TX-¡¢RX+¡¢RX- signals? Does netsilicon have some example apps to debug phy ? such as some loopback apps. I want to write a loopback apps.But I don’t know how to send and recv frames? Does it need socket? Appendix: My board use GTS fc518ls as transformer. Can it compatible with lxt971?