[问答] stm32f7+rt-thread移植lwip 的问题

各位网友你们好，用STM32f7搭载了rt-thread操作系统，移植lwip1.4.1版本的，网卡用的是lan8720, 网卡可以初始化程序，但是dhcp一直失败，打印信息如下，请问这个是什么问题呢？？？
netif->output()dhcp_discover: deleting()ing
dhcp_discover: SELECTING
dhcp_discover(): set request timeout 4000 msecs
dhcp_fine_tmr(): request timeout
dhcp_timeout()
dhcp_timeout(): restarting discovery
dhcp_discover()
transaction id xid(718021cb)
dhcp_discover: making request
dhcp_discover: realloc()ing
dhcp_discover: sendto(DISCOVER, IP_ADDR_BROADCAST, DHCP_SERVER_PORT)
udp_send: added header in given pbuf 20033584
udp_send: sending datagram of length 316
udp_send: UDP packet length 316
udp_send: UDP checksum 0x0000
udp_send: ip_output_if (,,,,IP_PROTO_UDP,)
ip_output_if: hg0
IP header:
+-------------------------------+
| 4 | 5 |  0x00 |       336     | (v, hl, tos, len)
+-------------------------------+
|        3      |000|       0   | (id, flags, offset)
+-------------------------------+
|  255  |   17  |    0x0000     | (ttl, proto, chksum)
+-------------------------------+
|    0  |    0  |    0  |    0  | (src)
+-------------------------------+
|  255  |  255  |  255  |  255  | (dest)
+-------------------------------+

netif->output()dhcp_discover: deleting()ing
dhcp_discover: SELECTING
dhcp_discover(): set request timeout 8000 msecs
dhcp_fine_tmr(): request timeout
dhcp_timeout()
dhcp_timeout(): restarting discovery
dhcp_discover()
transaction id xid(718021cb)
dhcp_discover: making request
dhcp_discover: realloc()ing
dhcp_discover: sendto(DISCOVER, IP_ADDR_BROADCAST, DHCP_SERVER_PORT)
udp_send: added header in given pbuf 20033584
udp_send: sending datagram of length 316
udp_send: UDP packet length 316
udp_send: UDP checksum 0x0000
udp_send: ip_output_if (,,,,IP_PROTO_UDP,)
ip_output_if: hg0
IP header:
+-------------------------------+
| 4 | 5 |  0x00 |       336     | (v, hl, tos, len)
+-------------------------------+
|        4      |000|       0   | (id, flags, offset)
+-------------------------------+
|  255  |   17  |    0x0000     | (ttl, proto, chksum)
+-------------------------------+
|    0  |    0  |    0  |    0  | (src)
+-------------------------------+
|  255  |  255  |  255  |  255  | (dest)
+-------------------------------+
netif->output()dhcp_discover: deleting()ing
dhcp_discover: SELECTING
dhcp_discover(): set request timeout 16000 msecs
dhcp_fine_tmr(): request timeout
dhcp_timeout()
dhcp_timeout(): restarting discovery
dhcp_discover()
transaction id xid(718021cb)
dhcp_discover: making request
dhcp_discover: realloc()ing
dhcp_discover: sendto(DISCOVER, IP_ADDR_BROADCAST, DHCP_SERVER_PORT)
udp_send: added header in given pbuf 20033584
udp_send: sending datagram of length 316
udp_send: UDP packet length 316
udp_send: UDP checksum 0x0000
udp_send: ip_output_if (,,,,IP_PROTO_UDP,)
ip_output_if: hg0
IP header: