Field Programming a Arduino with another Arduino with SD card over RX/TX lines

Question

I am not sure if this question has been asked before but here's what I wanted to do.

I have a Arduino Nano, which I need to update with a new sketch. The plan is to be able to use another Arduino (maybe a Nano again), with an SD card reader and a sketch loaded as HEX file on it. Then connect both using a 4 pin RX/TX/5V/GND and upload the sketch from the transmitter to the receiver. Is it possible?

I am not sure how to do this; I know I can use one Arduino as an ISP to update other, but I am thinking of streaming the hex file to the other. Has anyone done this, any hints would be extremely helpful.

Answer 1

There's actually a library for that as well! See here and here.

Answer 2

See What happens when code is uploaded using the bootloader?

There is a graphic on that page (reproduced below) which shows the general idea of what happens when you program using Tx/Rx after reset.

You could delve into the specs for the STK500 protocol (see linked page) and make your second Arduino follow that, to program from the SD card file.