嵌入式linux系统挂载不上NFS

请高手指点，关于内核中的设置，我已经参照网上的修改过了，可是每次都挂在不上NFS根目录，我用wireshark查看了，内核加载以后没有发出mount的数据包

[Boot] run nfsboot
egiga0 no link
port0 no link
port1 no link
port2 no link
port3 no link
port4 no link
port5 no link
port6 no link
port7 no link
port8 no link
Using port9 device
TFTP from server 192.168.1.20; our IP address is 192.168.1.254
Filename 'uImage'.
Load address: 0x2000000
Loading: #################################################################
#################################################################
#################################################################
########################################
done
Bytes transferred = 1198340 (124904 hex)
## Booting image at 02000000 ...
Image Name: Linux-2.6.22.18
Created: 2011-03-28 1:19:47 UTC
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 1198276 Bytes = 1.1 MB
Load Address: 00008000
Entry Point: 00008000
Verifying Checksum ... OK
OK

Checking for Linux kernel endianess at 0x02000040 = 0xe1a00000
Linux Kernel is LE

Starting kernel in LE mode ...
Uncompressing Linux................................................................................ done, booting the kernel.
Linux version 2.6.22.18 (root@debian) (gcc version 3.4.4 (release) (CodeSourcery ARM 2005q3-2)) #1 Mon Mar 28 09:19:25 CST 2011
CPU: ARM926EJ-S [56251311] revision 1 (ARMv5TE), cr=00053977
Machine: Feroceon-KW
Using UBoot passing parameters structure
BoardID from uboot=10
Memory policy: ECC disabled, Data cache writeback
calling iotable_init. MEM_TABLE=
virt=0xe7800000, phys=0x07800000, lengh=0x00800000
virt=0xe8000000, phys=0xe8000000, lengh=0x08000000
virt=0xf1000000, phys=0xf1000000, lengh=0x00100000
virt=0xf8000000, phys=0xf8000000, lengh=0x01000000
virt=0xf4000000, phys=0xf4000000, lengh=0x04000000
virt=0xfb000000, phys=0xfb000000, lengh=0x00010000
virt=0xf2000000, phys=0xf2000000, lengh=0x00010000
Internal prestera id register = 0x000dc343
xCat revision = A1
CPU0: D VIVT write-back cache
CPU0: I cache: 16384 bytes, associativity 4, 32 byte lines, 128 sets
CPU0: D cache: 16384 bytes, associativity 4, 32 byte lines, 128 sets
Built 1 zonelists. Total pages: 30480
Kernel command line: root=/dev/nfs rw nfsroot=192.168.1.20:/tftpboot/rootfs_arm-gnueabi ip=192.168.1.254:192.168.1.20::255.255.255.0::eth0:off console=ttyS0,115200 mtdparts=spi_flash:0x00100000(uboot)ro,0x001c0000(kernel),0x00d40000(rootfs)
PID hash table entries: 512 (order: 9, 2048 bytes)
Console: colour dummy device 80x30
Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
Memory: 120MB 0MB 0MB 0MB = 120MB total
Memory: 119168KB available (2260K code, 194K data, 88K init)
Mount-cache hash table entries: 512
CPU: Testing write buffer coherency: ok
NET: Registered protocol family 16

CPU Interface
-------------
SDRAM_CS0 ....base 00000000, size 128MB
SDRAM_CS1 ....disable
SDRAM_CS2 ....disable
SDRAM_CS3 ....disable
PEX0_MEM ....base e8000000, size 128MB
PEX0_IO ....base fc000000, size 1MB
INTER_REGS ....base f1000000, size 1MB
NFLASH_CS ....base d8000000, size 128MB
SPI_CS ....base f8000000, size 16MB
BOOT_ROM_CS ....no such
DEV_BOOTCS ....no such
CRYPT_ENG ....base fb000000, size 64KB
SAGE_UNIT ....base f4000000, size 64MB
DRAGONITE_DTCM ....base f2000000, size 64KB

Marvell Development Board (LSP Version KW_LSP_4.3.0.015)-- DB-98DX4122-48G Soc: 88F6281 A0 LE

Detected Tclk 200000000 and SysClk 320000000
Switch decoding windows init is done.
MV Buttons Device Load
PEX0 interface detected no Link.
PCI: bus0: Fast back to back transfers enabled
NET: Registered protocol family 2
Time: kw_clocksource clocksource has been installed.
IP route cache hash table entries: 1024 (order: 0, 4096 bytes)
TCP established hash table entries: 4096 (order: 3, 32768 bytes)
TCP bind hash table entries: 4096 (order: 2, 16384 bytes)
TCP: Hash tables configured (established 4096 bind 4096)
TCP reno registered
RTC has been updated!!!
RTC registered
Use the XOR engines (acceleration) for enhancing the following functions:
o RAID 5 Xor calculation
o kernel memcpy
o kenrel memzero
Number of XOR engines to use: 2
MV Buttons Driver Load
JFFS2 version 2.2. (NAND) ?? 2001-2006 Red Hat, Inc.
io scheduler noop registered
io scheduler anticipatory registered (default)
Serial: 8250/16550 driver $Revision: 1.90 $ 4 ports, IRQ sharing disabled
serial8250.0: ttyS0 at MMIO 0xf1012000 (irq = 33) is a 16550A
serial8250.0: ttyS1 at MMIO 0xf1012100 (irq = 34) is a 16550A
Loading Marvell Ethernet Driver:
o Uncached descriptors in DRAM
o DRAM SW cache-coherency
o Multi RX Queue support - 8 RX queues
o Multi TX Queue support - 8 TX Queues
o TCP segmentation offload enabled
o Receive checksum offload enabled
o Transmit checksum offload enabled
o Network Fast Processing (Routing) supported
o Driver ERROR statistics enabled
o Driver INFO statistics enabled
o Proc tool API enabled
o Rx descripors: q0=64 q1=64 q2=64 q3=64 q4=64 q5=64 q6=64 q7=64
o Tx descripors: q0=532 q1=532 q2=532 q3=532 q4=532 q5=532 q6=532 q7=532
o Loading network interface(s):
o eth0, ifindex = 1, GbE port = 0

Warning: Giga 1 is Forced Skipped Off

mvFpRuleDb (c70f4000): 1024 entries, 4096 bytes
NFTL driver: nftlcore.c $Revision: 1.98 $, nftlmount.c $Revision: 1.41 $
mvSFlashInit ERROR: Unknown SPI flash device!
ERROR: sflash_probe - Failed to initialize the SFlash.Using Hamming 1-bit ECC for NAND device
No NAND device found!!!
mice: PS/2 mouse device common for all mice
i2c /dev entries driver
TCP cubic registered
NET: Registered protocol family 1
NET: Registered protocol family 17
eth0: started
IP-Config: Complete:
device=eth0, addr=192.168.1.254, mask=255.255.255.0, gw=255.255.255.255,
host=192.168.1.254, domain=, nis-domain=(none),
bootserver=192.168.1.20, rootserver=192.168.1.20, rootpath=
Looking up port of RPC 100003/2 on 192.168.1.20
rpcbind: server 192.168.1.20 not responding, timed out
Root-NFS: Unable to get nfsd port number from server, using default
Looking up port of RPC 100005/1 on 192.168.1.20
rpcbind: server 192.168.1.20 not responding, timed out
Root-NFS: Unable to get mountd port number from server, using default
mount: server 192.168.1.20 not responding, timed out
Root-NFS: Server returned error -5 while mounting /tftpboot/rootfs_arm-gnueabi
VFS: Unable to mount root fs via NFS, trying floppy.
List of all partitions:
No filesystem could mount root, tried: jffs2
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)