[请问] No filesystem could mount root, tried: cramfs的问题

lsmslsms

我编译好内核，搭好文件系统烧到板子里，启动后，最后出现下面问题
uncorrectable error : <3>end_request: I/O error, dev mtdblock2, sector 256
isofs_fill_super: bread failed, dev=mtdblock2, iso_blknum=64, block=128
List of all partitions:
1f00             256 mtdblock0 (driver?)
1f01            2048 mtdblock1 (driver?)
1f02          257536 mtdblock2 (driver?)
No filesystem could mount root, tried:  cramfs vfat msdos iso9660 romfs
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(31,2)
[<c002d700>] (unwind_backtrace+0x0/0xdc) from [<c02892cc>] (panic+0x40/0x110)
[<c02892cc>] (panic+0x40/0x110) from [<c0008fcc>] (mount_block_root+0x1d0/0x210)
[<c0008fcc>] (mount_block_root+0x1d0/0x210) from [<c0009264>] (prepare_namespace+0x164/0x1bc)
[<c0009264>] (prepare_namespace+0x164/0x1bc) from [<c0008598>] (kernel_init+0xb4/0xe0)
[<c0008598>] (kernel_init+0xb4/0xe0) from [<c004912c>] (do_exit+0x0/0x578)
[<c004912c>] (do_exit+0x0/0x578) from [<00000001>] (0x1)

进不到系统里，大概是什么问题啊，，，没头绪。。。