备份 Nand Flash 存储区

板载 Linux 版本 2.6.26.5 嵌入式系统。设备使用完整图像的内核。存储在 NAND 闪存上的文件系统，Hynix NAND 32MiB 3,3V 8 位。

# printenv
baudrate=115200
ethaddr=FF:FF:FF:FF:FF:FF
netmask=255.255.255.0
ipaddr=192.168.1.1
serverip=192.168.1.100
bootfile=firetux.kernel
bootcmd1=setenv bootargs ${bootargs} && nboot 0x20200000 0 ${image_addr} && bootm 0x20200000
bootcmd2=setenv bootargs ${bootargs} && tftpboot 20200000 firetux.kernel && bootm 20200000
phymode=auto
mtdids=nand0=gen_nand
unlock=yes
verify=y
update.uboot=echo Update u-boot && tftpboot 0x20000000 nandboot.flash && nand erase 0x0 0x03ffff && nand write.jffs2 0x20000000 0x0 ${filesize}
update.kernel=echo Update kernel && tftpboot 0x20000000 uImage && nand erase 0x80000 0x180000 && nand write.jffs2 20000000 0x80000 0x180000
update.romimg=echo Update RomImage && tftpboot 0x20000000 romimage.img && nand erase 0x80000 0x13e0000&& nand write.jffs2 20000000 0x80000 ${filesize}
update.halfimg=echo Update HalfImage && tftpboot 0x20000000 recovery.img && nand erase 0x1460000 0x700000&& nand write.jffs2 20000000 0x1460000 ${filesize}
eraseenv=echo Erase Environment && nand erase 0x60000 0x20000
HwModel=Hw_Model=NXPi02
bootcmd=run bootcmd1
halfImage=half_image=0
cy_boot_code_ver=1.0.1 (Oct  6 2011 - 20:04:00)
RouterMode=Router_Mode=0
stdin=serial
stdout=serial
stderr=serial
bootcmd=run bootcmd1
image_addr=0x80000
bootargs=console=ttyS1,115200n8 rootfstype=squashfs noalign half_image=0 verify=y Hw_Model=NXPi02 Router_Mode=0
ethact=ETN1
bootdelay=3

需要从 U-boot 备份 NAND 内存 (NVRAM) 的某些区域，通过串行接口 (UART) 连接到板，网络连接不可用。U-boot 有一些管理 nand 内存的选项：

# help nand
nand info - show available NAND devices
nand device [dev] - show or set current device
nand read - addr off|partition size
nand write - addr off|partition size
    read/write 'size' bytes starting at offset 'off'
    to/from memory address 'addr', skipping bad blocks.
nand erase [clean] [off size] - erase 'size' bytes from
    offset 'off' (entire device if not specified)
nand bad - show bad blocks
nand dump[.oob] off - dump page
nand scrub - really clean NAND erasing bad blocks (UNSAFE)
nand markbad off - mark bad block at offset (UNSAFE)
nand biterr off - make a bit error at offset (UNSAFE)

尤其是，nand dump[.oob] off - dump page

什么是 nand偏移地址？没有指定要转储的分区大小。我需要转储整个 NVRAM。

设备加载内核映像后，会创建 11 个 MTD 分区：

Creating 11 MTD partitions on "gen_nand":
0x00000000-0x00060000 : "u-boot"
0x00060000-0x00080000 : "u-bootenv"
0x00080000-0x01460000 : "ROMIMAGE"
0x01460000-0x01b60000 : "HALFIMAGE"
0x00200000-0x01460000 : "LINUX_ROOTFS"
0x01b60000-0x01d60000 : "HS_FW"
0x01d60000-0x01e60000 : "FPAR"
0x01e60000-0x01ee0000 : "SNOM"
0x01ee0000-0x01f00000 : "EEPROM"
0x01f00000-0x01f80000 : "NVRAM"
0x01f80000-0x02000000 : "CA_DATA"

是0x01f00000nvram 偏移地址吗？什么是 nvram 大小？是0x80000吗？U-boot也有命令md - memory display。

=> help md
md - memory display
Usage:
md [.b, .w, .l] address [# of objects]
=>

我尝试md.b 0x01f00000 0x80000在终端上显示 nvram 的命令，但它不输出任何内容，终端挂断。

编辑：[补充]

# nand info

Device 0: NAND 32MiB 3,3V 8-bit, sector size 16 KiB
# nand device nand0
Device 0: NAND 32MiB 3,3V 8-bit... is now current device
# nand read 0x20000000 NVRAM

NAND read: mtdparts variable not set, see 'help mtdparts'
incorrect device type in NVRAM
'NVRAM' is not a number
# nand read 0x20000000 0x01f00000 0x00080000

NAND read: device 0 offset 0x1f00000, size 0x80000
 524288 bytes read: OK

BusyBox v1.10.2 (2015-09-06 10:58:05 CST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

/bin/sh: can't access tty; job control turned off
# help

Built-in commands:
-------------------
    . : [ [[ alias bg break cd chdir continue echo eval exec exit
    export false fg hash help jobs let local pwd read readonly return
    set shift source test times trap true type ulimit umask unalias
    unset wait

# ext4write LINUX_ROOTFS /NVRAM.img 0x20000000 0x00080000
/bin/sh: ext4write: not found