Documentation of initial GCW Zero image build process research

2022-10-25 07:25:22 +00:00
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+Custom GCW Zero OS Image
+------------------------
+
+This page serves to record everything I've learned about building an OS Image for the GCW Zero.
+
+Existing Images
+===============
+- `The official image <http://gcw-zero.com/flashing>`_
+    - This was last updated 2015-07-23
+    - This is based on OpenDingux
+- `Current OpenDingux development images <https://github.com/OpenDingux/buildroot>`_
+    - GCW Zero update packages, odboot binaries, and toolchains are available `here <https://github.com/OpenDingux/buildroot/releases>`_.
+    - These are automatically? built by GitHub actions.
+    - Work to bring OpenDingux / device support to newer Linux Kernel versions is supposedly happening in this repo
+- `Adam Image <https://github.com/eduardofilo/RG350_adam_image>`_
+    - This is built on top of the newer OpenDingux releases.
+    - Currently this seems to be fixed to a version from `2022-02-13 <https://github.com/eduardofilo/RG350_adam_image/blob/81b3e833640b8f1db69371dae47dabe248690dc9/build.sh#L6>`_.
+    - This image opens up the OpenDingux image and creates a modified userspace with a different launcher and newer appliactions.
+    - The boot flow seems to be identical to the OpenDingux upstream.
+    
+Boot Flow
+=========
+`UBIBoot <https://github.com/pcercuei/UBIBoot>`_
+_______
+- Bootloader for launching a Linux Kernel off a UBI partition
+- This seems like it is used all over the place, but none of the images that I've looked at are using an UBI partition.
+    - They have been FAT32
+    - I should double check this, otherwise I'm a bit confused here.
+    - Maybe all the SDCard images have this program written to their first 512 bytes (MBR style)
+        - This would explain why the base offset for the `/boot` partition on the images is such a high number
+        - Is there a UBI partition that launches before the kernel in the FAT32 partition is loaded?
+        - This would probably not be visible when mounting the images
+        - I should reinvestigate this
+            - The Adam Image build scripts would probably be a good reference
+        
+
+Kernel
+______
+
+- It is probably best to use the OpenDingux built kernel for now.
+    - It looks like there is some upstreaming working being done, but the status of that in unknown.
+    - It would be cool to extract this from the buildroot flow so it could be built independently.
+- One known issue with the latest OpenDingux kernel is that the display output doesn't work.
+    - This seems to be due to a conflict in the HDMI driver.
+        - I think disabling HDMI or removing the kernel module if there one might work around this.
+    - This might be fixed now based on `this thread <https://github.com/eduardofilo/RG350_adam_image/issues/262>`_ on the Adam Image issue tracker.
+        - I think this was a seperate issue based on the fact that the `fix <https://github.com/eduardofilo/RG350_adam_image/commit/f2c60849c90eb3ba6aab196604e8f66cce6b1d6e>`_ was in the Adam Image build scripts.
+            - Adam Image is using too old of a OpenDingux base to have hit this issue, as it was discovered in May 2022 [1]_
+        - One interesting tidbit from this thread is that the `OpenDingux maintainer seems to be working on fixing this issue <https://github.com/eduardofilo/RG350_adam_image/issues/262#issuecomment-1168830000>`_.
+            - This is helpful, as the github issue that this same person opened has no replies. [1]_
+            - This person might be overstating that the maintainer knowns, not sure here.
+
+`Mininit <https://github.com/OpenDingux/mininit>`_
+_______
+- Mininit is a bootloader that allows loading the root filesystem from a squashfs image called `rootfs.squashfs`.
+- It also supports loading kernel modules from a squashfs image called `modules.squashfs`.
+- After it mounts all the required filesystems, control is handed off to the `/sbin/init` binary in the mounted rootfs [2]_.
+
+
+
+Booting Debian
+==============
+
+Creating a boot partition
+_________________________
+- TODO
+
+Creating a mips32le squashfs rootfs
+___________________________________
+- `Docker based flow to build rootfs <https://git.ohea.xyz/gcwzero/debian-rootfs>`_
+
+Creating a sdcard image
+_______________________
+- TODO
+
+Packaging the Kernel as a `.deb`
+________________________________
+- TODO
+
+Packaging userspace applications as `.deb`s
+___________________________________________
+- TODO
+
+Creating package repo for serving updates
+_________________________________________
+- TODO
+
+Useful Links
+============
+- `OpenDingux blog post on new kernel and device tree cleanup work <https://opendingux.net/opendingux/2020/06/09/update-on-gcw-zero-20200531.html>`_
+
+
+Citations
+=========
+.. [1] https://github.com/OpenDingux/buildroot/issues/77
+.. [2] https://github.com/OpenDingux/mininit#rootfs-image-layout