Steps needed to patch update.upt with rockbox bootloader are explained in
bootloader_install.sh shell script. Process is quite involved and some
custom tools are needed.


For convenience Dockerfile is provided which prepares custom image based
on debian 9 which has all the tools needed to work with Agptek Rocker update
images.

Basically image extends standard debian image by:
1) Installing developer packages from stock debian
2) Cloning https://github.com/wodz/rockbox-wodz.git
3) Building custom cross toolchain
4) Cloning and installing tools to work with UBIFS

You first need to build image with:
docker build . -t "agptek-dev"

Then you can start container and work with update.upt.
If you want to generate patched update image in automatic way:
docker run --rm -it -v /path/to/dir/with/update.upt:/upt \
-e UPT_DIR=/upt agptek-dev bootloader_install.sh

Patched update.upt with rockbox bootloader and rockbox.zip should end up in
specified directory.

If you want to play around, hack something etc. you can run container in
interactive mode:
docker run -it -v /path/to/dir/with/update.upt:/upt \
-e UPT_DIR=/upt agptek-dev bash


Files in this directory:
README - this file
bootloader_install.sh - shell script documenting process of patching
                        agptek rocker update images

update_update.py      - little helper utility to patch update.txt
                        controll file

hiby_player.sh        - shell script called on player boot which
                        originally started music player application
                        and now it starts bootloader

Dockerfile            - file to build docker image with all needed
                        tools to play with agptek rocker files