How to NFS boot from Eth1 (2ed netcard) instead eth0 on board DM8168evm-revJ

hello,

     I wanna boot my board from the second net card, but the uboot can't find it,

there is the Uboot boot log:

.....
TI8168-GP rev 2.1
ARM clk: 987MHz
DDR clk: 796MHz

I2C:   ready
DRAM:  2 GiB
NAND:  HW ECC BCH8 Selected
256 MiB
MMC:   OMAP SD/MMC: 0

Net:   Detected MACID:50:56:63:a7:8d:a5
Ethernet PHY: GENERIC @ 0x01
DaVinci EMAC
Hit any key to stop autoboot:  0

....

when i powered on. it seems like not configure the eth1 in Uboot .

what should I do, or any reference for this problem. thanks ..