Update uboot from serial like openwrt router

[boobypi]

Hi!

I would like to know if there is a way at the startup to load new uboot / system to sdcard or spi flash.
The fact is for DIY waterproof system, it's hard to remove sdcard, sometimes OPi isn't close of my computer.

Idealy i would like TFTP / serial upgrade like openwrt router.
Maybe it's impossible since TFTP upgrade need to download before image to ram, check it and burn it.
With OP PC we have 1G ram to store image before write it on sdcard...

Any idea?

thanks

[boobypi]

ofcourse i have an acces to serial over the air (esp8266)