通过u-boot把内核和文件系统烧录到Nand Flash

前提条件：
板子可以启动到u-boot环境；
内核文件、文件系统都准备好而且能正常运行；
tftp服务器打开；

测试环境：
AT91SAM9263-EK；
 
设置板子和tftp服务器的ip地址以及板子的mac地址；
U-Boot>setenv ipaddr 192.168.1.2
U-Boot>setenv serverip 192.168.1.100
U-Boot>setenv ethaddr 0:1:2:3:4:5

通过tftp下载内核文件vmlinux和文件系统ramdisk.gz，并将他们写入Nand Flash中；
先擦除flash
U-Boot>nand scrub 或者 nand erase
下载并写入flash
U-Boot>tftp 0x22000000 vmlinux
U-Boot>nand write 0x22000000 0x0 0x200000
U-Boot>tftp 0x22000000 ramdisk.gz
U-Boot>nand write 0x22000000 0x400000 0x300000
从Nand Flash读出内核和文件系统到SDRAM上，注意此处读出操作可以省，只要上一步的下载地址指定好既可；
U-Boot>nand read 0x22000000 0x0 0x16c58a (vmlinux大小)
U-Boot>nand read 0x20500000 0x400000 0x24bc12 (ramdisk.gz大小)
从SDRAM启动系统
U-Boot>go 0x22000000
如果能正确运行系统，烧录文件到Nand Flash成功。

自动启动（自动从Nand Flash拷贝文件到SDRAM里），设置U-boot的环境变量：
U-Boot>setenv bootcmd nand read 0x22000000 0x0 0x16c58a/;nand read 0x20500000 0x400000 0x24bc12/;go 0x22000000
U-Boot>saveenv
reset板子即可。
 
附上U-boot下Nand Flash的相关命令(u-boot-<version>/common/cmd_nand.c -- U_BOOT_CMD) ：

"nand - NAND sub-system/n",     "info - show available NAND devices/n"     "nand device [dev] - show or set current device/n"     "nand read[.jffs2] - addr off|partition size/n"     "nand write[.jffs2] - addr off|partiton size - read/write `size' bytes starting/n"     " at offset `off' to/from memory address `addr'/n"     "nand erase [clean] [off size] - erase `size' bytes from/n"     " offset `off' (entire device if not specified)/n"     "nand bad - show bad blocks/n"     "nand dump[.oob] off - dump page/n"     "nand scrub - really clean NAND erasing bad blocks (UNSAFE)/n"     "nand markbad off - mark bad block at offset (UNSAFE)/n"     "nand biterr off - make a bit error at offset (UNSAFE)/n"     "nand lock [tight] [status] - bring nand to lock state or display locked pages/n"     "nand unlock [offset] [size] - unlock section/n";