内存加到1G后，发现后面的512M不能使用，导致kernel起不来，停在starting kernel那里。
所以在uboot环境下检测后面512M内存：
uboot下sflash 地址为0xf8000000，前100000为uboot，后面的为kernel
Marvell>> iminfo 0xf8100000
## Checking Image at f8100000 ...
Image Name: Linux-2.6.31.8
Created: 2011-06-19 8:36:25 UTC
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 4419220 Bytes = 4.2 MB
Load Address: 00008000
Entry Point: 00008000
Verifying Checksum ... OK
读取kernel到内存某地址，再和sflash中的内容比较，就能检测内存是否错误：
setenv loadaddr 0x02000000
sflash read 0x100000 $(loadaddr) 0x500000
cmp.b $(loadaddr) 0xf8100000 0x500000
读取到512M位置，发现比较错误。
setenv loadaddr 0x20000000
Marvell>> sflash read 0x100000 $(loadaddr) 0x500000
Marvell>> cmp.b $(loadaddr) 0xf8100000 0x500000
byte at 0x20000000 (0x9f) != byte at 0xf8100000 (0x27)
Total of 0 bytes were the same