[U-Boot] unlock NVRAM for writing from within U-boot shell

[Alex]

Embedded Linux device: how is performed NVRAM update?
For example, updates of firmware, u-boot, uimage and other are performed from U-Boot, here sample code from U-boot:

update_uboot=tftpboot 0x80000100 u-boot.bin && protect off 0x48000000 +${filesize} && erase 0x48000000 +${filesize} && sleep ${sdelay} && cp.b ${fileaddr} 0x48000000 ${filesize} && protect on 0x48000000 +${filesize}

update_uimage=tftpboot 0x80000100 uImage && protect off ${UBFIADDR1} +${filesize} && erase ${UBFIADDR1} +${filesize} && sleep ${sdelay} && cp.b ${fileaddr} ${UBFIADDR1} ${filesize} && protect on ${UBFIADDR1} +${filesize}

There is no any directions or tips related to NVRAM update in U-boot code. The nvram.bin offset address is specified in code, so is it possible to write to NVRAM from U-boot shell mode? (even if there is no directions on U-boot) If yes, how to unlock NVRAM for writing from within u-boot shell?

Spansion Serial Flash FLASH_S25FL064A

here is U-boot dump with all commands inside:
http://pastebin.com/raw.php?i=W6mnfUaq