why cann't boot uclinux from sd card

hi all,

After,I mounted sd card over spi successfull,I followed the root device topic(http://www.nioswiki.com/operatingsystems/uclinux/rootdevice), step by step ,but cann't boot from sd card. and always show the message as

test1:

====================================================

VFS: Cannot open root device "mmcblk0p1 rw rootfstype=jffs2" or unknown-block(0,

0)

Please append a correct "root=" boot option; here are the available partitions:

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

uClinux/Nios II

Built 1 zonelists in Zone order, mobility grouping off. Total pages: 2032

Kernel command line: root=/dev/mmcblk0 rw rootfstype=jffs2

PID hash table entries: 32 (order: 5, 128 bytes)

Dentry cache hash table entries: 1024 (order: 0, 4096 bytes)

Inode-cache hash table entries: 1024 (order: 0, 4096 bytes)

Memory available: 5816k/2095k RAM, 0k/0k ROM (1791k kernel code, 304k data)

Mount-cache hash table entries: 512

net_namespace: 180 bytes

NET: Registered protocol family 16

NET: Registered protocol family 2

IP route cache hash table entries: 1024 (order: 0, 4096 bytes)

TCP established hash table entries: 512 (order: 0, 4096 bytes)

TCP bind hash table entries: 512 (order: -1, 2048 bytes)

TCP: Hash tables configured (established 512 bind 512)

TCP reno registered

NET: Registered protocol family 1

io scheduler noop registered

io scheduler deadline registered (default)

ttyJ0 at MMIO 0x19020a0 (irq = 1) is a Altera JTAG UART

console [ttyJ0] enabled

ttyS0 at MMIO 0x1902000 (irq = 2) is a Altera UART

dm9000 Ethernet Driver, V1.30

mmc_spi spi2.0: ASSUMING SPI bus stays unshared!

mmc_spi spi2.0: ASSUMING 3.2-3.4 V slot power

mmc_spi spi2.0: SD/MMC host mmc0, no DMA, no WP, no poweroff

TCP cubic registered

NET: Registered protocol family 17

RPC: Registered udp transport module.

RPC: Registered tcp transport module.

VFS: Cannot open root device "mmcblk0" or unknown-block(0,0)

Please append a correct "root=" boot option; here are the available partitions:

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

====================================================

test2:

====================================================

VFS: Cannot open root device "mmcblk0p1" or unknown-block(0,0)

Please append a correct "root=" boot option; here are the available partitions:

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

====================================================

test3:

====================================================

VFS: Cannot open root device "mmcblk0" or unknown-block(0,0)

Please append a correct "root=" boot option; here are the available partitions:

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

====================================================

and the kernel command line is "root=/dev/mmcblk0p1 rw",or "root=/dev/mmcblk0 rw",

Are there anybody can tell me ,what should I do?

THX!