linux按照系统移植手册做到step11，发现系统不能引导

linux按照系统移植手册做到step11，发现系统不能引导，发现如下错误：
Root-NFS: No NFS server available, giving up.
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "nfs" or unknown-block(2,0)
Please append a correct "root=" boot option; here are the available partitions:
1f00        256 mtdblock0 (driver?)
1f01       2048 mtdblock1 (driver?)
1f02      61472 mtdblock2 (driver?)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)

请问是怎么回事啊？谢谢

具体信息如下：
Enter your selection: 8
Start Linux ...
Copy linux kernel from 0x001f0000 to 0x30008000, size = 0x00200000 ... Copy Kern
el to SDRAM done,NOW, Booting Linux......
Uncompressing Linux.............................................................
............................................ done, booting the kernel.
Linux version 2.6.25.8 (root@xmu-hujun) (gcc version 3.4.1) #1 Thu Jul 9 15:53:4
1 CST 2009
CPU: ARM920T [41129200] revision 0 (ARMv4T), cr=c0007177
Machine: SMDK2440
ATAG_INITRD is deprecated; please update your bootloader.
Memory policy: ECC disabled, Data cache writeback
CPU S3C2440A (id 0x32440001)
S3C244X: core 400.000 MHz, memory 100.000 MHz, peripheral 50.000 MHz
S3C24XX Clocks, (c) 2004 Simtec Electronics
CLOCK: Slow mode (1.500 MHz), fast, MPLL on, UPLL on
CPU0: D VIVT write-back cache
CPU0: I cache: 16384 bytes, associativity 64, 32 byte lines, 8 sets
CPU0: D cache: 16384 bytes, associativity 64, 32 byte lines, 8 sets
Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 16256
Kernel command line: console=ttySAC0 root=/dev/nfs nfsroot=:/opt/EmbedSky/root_n
fs ip=::::SKY2440.embedsky.net:eth0:off
irq: clearing subpending status 00000003
irq: clearing subpending status 00000002
PID hash table entries: 256 (order: 8, 1024 bytes)
timer tcon=00500000, tcnt a2c1, tcfg 00000200,00000000, usec 00001eb8
Console: colour dummy device 80x30
console [ttySAC0] enabled
Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)
Inode-cache hash table entries: 4096 (order: 2, 16384 bytes)
Memory: 64MB = 64MB total
Memory: 61440KB available (3020K code, 287K data, 124K init)
Mount-cache hash table entries: 512
CPU: Testing write buffer coherency: ok
net_namespace: 152 bytes
NET: Registered protocol family 16
S3C2410 Power Management, (c) 2004 Simtec Electronics
S3C2440: Initialising architecture
S3C2440: IRQ Support
S3C24XX DMA Driver, (c) 2003-2004,2006 Simtec Electronics
DMA channel 0 at c4800000, irq 33
DMA channel 1 at c4800040, irq 34
DMA channel 2 at c4800080, irq 35
DMA channel 3 at c48000c0, irq 36
S3C244X: Clock Support, DVS off
usbcore: registered new interface driver usbfs
usbcore: registered new interface driver hub
usbcore: registered new device driver usb
NET: Registered protocol family 2
IP route cache hash table entries: 1024 (order: 0, 4096 bytes)
TCP established hash table entries: 2048 (order: 2, 16384 bytes)
TCP bind hash table entries: 2048 (order: 1, 8192 bytes)
TCP: Hash tables configured (established 2048 bind 2048)
TCP reno registered
NetWinder Floating Point Emulator V0.97 (double precision)
JFFS2 version 2.2. (NAND) 漏 2001-2006 Red Hat, Inc.
fuse init (API version 7.9)
yaffs Jul  9 2009 15:51:24 Installing.
io scheduler noop registered
io scheduler anticipatory registered (default)
io scheduler deadline registered
io scheduler cfq registered
Console: switching to colour frame buffer device 30x40
fb0: s3c2410fb frame buffer device
lp: driver loaded but no devices found
ppdev: user-space parallel port driver
Serial: 8250/16550 driver $Revision: 1.90 $ 4 ports, IRQ sharing enabled
s3c2440-uart.0: s3c2410_serial0 at MMIO 0x50000000 (irq = 70) is a S3C2440
s3c2440-uart.1: s3c2410_serial1 at MMIO 0x50004000 (irq = 73) is a S3C2440
s3c2440-uart.2: s3c2410_serial2 at MMIO 0x50008000 (irq = 76) is a S3C2440
brd: module loaded
loop: module loaded
dm9000 Ethernet Driver, V1.30
Uniform Multi-Platform E-IDE driver
ide: Assuming 50MHz system bus speed for PIO modes; override with idebus=xx
S3C24XX NAND Driver, (c) 2004 Simtec Electronics
s3c2440-nand s3c2440-nand: Tacls=2, 20ns Twrph0=3 30ns, Twrph1=2 20ns
NAND device: Manufacturer ID: 0xec, Chip ID: 0x76 (Samsung NAND 64MiB 3,3V 8-bit
)
Scanning device for bad blocks
Creating 3 MTD partitions on "NAND 64MiB 3,3V 8-bit":
0x00000000-0x00040000 : "TQ2440_uboot"
0x0004c000-0x0024c000 : "TQ2440_kernel"
0x0024c000-0x03ffc000 : "TQ2440_yaffs2"
usbmon: debugfs is not available
s3c2410-ohci s3c2410-ohci: S3C24XX OHCI
s3c2410-ohci s3c2410-ohci: new USB bus registered, assigned bus number 1
s3c2410-ohci s3c2410-ohci: irq 42, io mem 0x49000000
usb usb1: configuration #1 chosen from 1 choice
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 2 ports detected
mice: PS/2 mouse device common for all mice
S3C24XX RTC, (c) 2004,2006 Simtec Electronics
s3c2440-i2c s3c2440-i2c: slave address 0x10
s3c2440-i2c s3c2440-i2c: bus frequency set to 390 KHz
s3c2440-i2c s3c2440-i2c: i2c-0: S3C I2C adapter
S3C2410 Watchdog Timer, (c) 2004 Simtec Electronics
s3c2410-wdt s3c2410-wdt: watchdog inactive, reset disabled, irq enabled
TCP cubic registered
NET: Registered protocol family 1
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
drivers/rtc/hctosys.c: unable to open rtc device (rtc0)
drivers/rtc/hctosys.c: unable to open rtc device (rtc0)
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "nfs" or unknown-block(2,0)
Please append a correct "root=" boot option; here are the available partitions:
0100       4096 ram0 (driver?)
0101       4096 ram1 (driver?)
0102       4096 ram2 (driver?)
0103       4096 ram3 (driver?)
0104       4096 ram4 (driver?)
0105       4096 ram5 (driver?)
0106       4096 ram6 (driver?)
0107       4096 ram7 (driver?)
0108       4096 ram8 (driver?)
0109       4096 ram9 (driver?)
010a       4096 ram10 (driver?)
010b       4096 ram11 (driver?)
010c       4096 ram12 (driver?)
010d       4096 ram13 (driver?)
010e       4096 ram14 (driver?)
010f       4096 ram15 (driver?)
1f00        256 mtdblock0 (driver?)
1f01       2048 mtdblock1 (driver?)
1f02      63168 mtdblock2 (driver?)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)

没有文件系统导致的。

我也出现这种情况，但下了文件系统后还是不行

怎么就编译不出来天嵌做好的那个镜像呢？

你可以看下你的编译出来的zImage多大？
之前我遇到zImage > 2M，但是Uboot里面只分配了2M空间给zImage，然后flash FS的时候就把zImage > 2M的空间也清空了，这样好像也会遇到这个问题。