nfs下载启动内核出现如下问题

hi 我在尝试用nfs下载启动内核的时候出现如下问题，应该是什么原因引起的呢？

OpenJTAG> nfs 32000000 192.168.31.115:/home/book/work/linux-3.4.2/arch/ARM/boot/uImage;bootm 32000000
dm9000 i/o: 0x20000000, id: 0x90000a46
DM9000: running in 16 bit mode
MAC: 08:00:3e:26:0a:5b
could not establish link
File transfer via NFS from server 192.168.31.115; our IP address is 192.168.31.114
Filename '/home/book/work/linux-3.4.2/arch/arm/boot/uImage'.
Load address: 0x32000000
Loading: *** ERROR: Cannot mount
timeou