eboot网口下载问题

eboot使用TFTP下载时，出现下面情况：
Enter your selection: d
CS8900: MAC Address: 10:23:45:67:89:ab
INFO: Probe: DM9000 is detected.
INFO: Init: DM9000_Init OK.
+EbootSendBootmeAndWaitForTftp
Sent BOOTME to 255.255.255.255
Sent BOOTME to 255.255.255.255
Sent BOOTME to 255.255.255.255
Sent BOOTME to 255.255.255.255
Sent BOOTME to 255.255.255.255
Sent BOOTME to 255.255.255.255
Sent BOOTME to 255.255.255.255
Sent BOOTME to 255.255.255.255
Packet has the following data:
  boot.bin[NULL]octet[NULL]
TFTP packet could have 1 name/value pairs
Locked Down Link 1
Src IP 192.168.1.8 Port 03D4   Dest IP 192.168.1.96 Port DFAB
Default TFTP block size set to: 512 bytes
There were no options detected in the TFTP
EthDown::TFTPD_OPEN::boot.bin
-EbootSendBootmeAndWaitForTftp
USB host is not connected yet.
就在这里卡住了，最诡异的是最后一句居然是USB host is not connected yet.，也仔细查看过代码，发现就是不能执行OEMPreDownload( )后面的函数，一直没有查出问题，代码没道理不执行下面的函数的，怎么会跳到USB host is not connected yet.这里呢？

亲，你想用eboot的网络下载方式吗？天嵌科技的eboot已经提供了usb下载方式了，更方便。