Who can give me a favor?
"root=nfs" is wrong?

++++++++++++++++++++++++++++++++++++
losh> load elf tftp/192.168.1.18:/vmlinux
loading from /tftp/192.168.1.18:/vmlinux:
R...........
elf file type : 0x0002
machine type: 0028 version: 1
prog start addr : 0x200c8000
num prog headers: 1
num sect headers: 10
offset : 0x00008000 disk length: 0x00157c73 mem len: 0x0017f39c
phyaddr: 0x200c8000 vaddr : 0x200c8000 dl addr: 0x200c8000
losh> exec ip=dhcp root=nfs
kernel cmdline: 'ip=dhcp root=nfs' at 200c0100
Linux version 2.4.17-rmk2-lineo5 (root@localhost.localdomain) (gcc version 2.95.
3 20010315 (release)) #2 Mon Oct 24 01:13:27 UTC 2005
Processor: ARM ARM720T revision 3
Architecture: LogicPD LH79520 Card Engine
On node 0 totalpages: 8192
zone(0): 8192 pages.
zone(1): 0 pages.
zone(2): 0 pages.
Kernel command line: console=ttyAM1,115200 ip=dhcp root=nfs
setup_timer(): timerLoad=32256
Console: colour dummy device 80x30
Calibrating delay loop... 25.70 BogoMIPS
Memory: 32MB = 32MB total
Memory: 14288KB available (1206K code, 250K data, 76K init)
Dentry-cache hash table entries: 4096 (order: 3, 32768 bytes)
Inode-cache hash table entries: 2048 (order: 2, 16384 bytes)
Mount-cache hash table entries: 512 (order: 0, 4096 bytes)
Buffer-cache hash table entries: 1024 (order: 0, 4096 bytes)
Page-cache hash table entries: 8192 (order: 3, 32768 bytes)
POSIX conformance testing by UNIFIX
Linux NET4.0 for Linux 2.4
Based upon Swansea University Computer Society NET3.039
Initializing RT netlink socket
Starting kswapd
ttyAM0 at MEM 0xfffc0000 (irq = 23) is a AMBA PrimeCell PL011
ttyAM1 at MEM 0xfffc1000 (irq = 24) is a AMBA PrimeCell PL011
ttyAM2 at MEM 0xfffc2000 (irq = 25) is a AMBA PrimeCell PL011
Console: switching to colour frame buffer device 30x40
LH79520 Watchdog Timer: timer margin 60 sec
block: 64 slots per queue, batch=16
RAMDISK driver initialized: 16 RAM disks of 8192K size 1024 blocksize
hd: no drives specified - use hd=cyl,head,sectors on kernel command line
hd?: reset timed out: status=0x33 { WriteFault SeekComplete Index Error }
hd?: reset timed out: error=0x33 { SectorIdNotFound TrackZeroNotFound AddrMarkNo
tFound }, CHS=13066/10/51
hd: controller still busy
hd?: reset timed out: status=0x33 { WriteFault SeekComplete Index Error }
hd?: reset timed out: error=0x33 { SectorIdNotFound TrackZeroNotFound AddrMarkNo
tFound }, CHS=13066/10/51
hd: controller still busy
hd?: reset timed out: status=0x33 { WriteFault SeekComplete Index Error }
hd?: reset timed out: error=0x33 { SectorIdNotFound TrackZeroNotFound AddrMarkNo
tFound }, CHS=13066/10/51
hd: controller still busy
eth0: SMC91C11xFD(rev:1) at 0xf4800000 IRQ:4 DMA:0 (16-bit) MEM:8192b NOWAIT:1
eth0: ADDR: 00:08:ee:00:12:44
NET4: Linux TCP/IP 1.0 for NET4.0
IP Protocols: ICMP, UDP, TCP
IP: routing cache hash table of 512 buckets, 4Kbytes
TCP: Hash tables configured (established 2048 bind 2048)
Sending BOOTP requests . OK
IP-Config: Got BOOTP answer from 192.168.1.18, my address is 192.168.1.200
IP-Config: Complete:
device=eth0, addr=192.168.1.200, mask=255.255.255.0, gw=192.168.1.1,
host=192.168.1.200, domain=, nis-domain=(none),
bootserver=192.168.1.18, rootserver=192.168.1.18, rootpath=
NET4: Unix domain sockets 1.0/SMP for Linux NET4.0.
NetWinder Floating Point Emulator V0.95 (c) 1998-1999 Rebel.com
RAMDISK: Couldn't find valid RAM disk image starting at 0.
Freeing initrd memory: 16384K
Looking up port of RPC 100003/2 on 192.168.1.18
Looking up port of RPC 100005/1 on 192.168.1.18
Root-NFS: Server returned error -13 while mounting /tftpboot/192.168.1.200
VFS: Unable to mount root fs via NFS, trying floppy.
request_module[block-major-2]: Root fs not mounted
VFS: Cannot open root device "nfs" or 02:00
Please append a correct "root=" boot option
Kernel panic: VFS: Unable to mount root fs on 02:00