DE2-uclinux,Kernel panic - not syncing: VFS:unknow

Hello,Everyone!

My board is DE2.Its configurations are as follows:

SDRAM,8Mbytes;CFI Flash:1M.

I build the uclinux kernel ,the size if vmlinuz.bin is smaller than 800KBytes.

We upload the kernel sucessfully. But when we run,the messages tell:

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Built 1 zonelists

Kernel command line: root=/dev/sdram ro

PID hash table entries: 64 (order: 6, 1024 bytes)

Dentry cache hash table entries: 2048 (order: 1, 8192 bytes)

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

Memory available: 7324k/8192k RAM, 0k/0k ROM (633k kernel code, 116k data)

Mount-cache hash table entries: 512 (order: 0, 4096 bytes)

Linux NoNET1.0 for Linux 2.6

Serial: JTAG UART driver $Revision: 1.4 $

ttyJ0 at MMIO 0x81004000 (irq = 1) is a jtag_uart

io scheduler noop registered

io scheduler anticipatory registered

io scheduler deadline registered

io scheduler cfq registered

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

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Will any one give me a hand?

Thanks in advance!