Developer Guide

These are guidelines that should be followed when doing Replicant development.

Prerequisites

Developing on Replicant isn't much harder than developing on any other free software project as it doesn't require specific knowledge. In fact, you'll probably learn a lot along the way regarding how hardware works, how the Android system is composed, how the kernel works, etc, but you don't need to know all of this to start. However a basic set of skills is required, among which:
  • C language programming skills and the ability to understand other languages such as C++ and Java
  • Makefile skills (no need to know every detail about it, a general idea of how Makefiles work is enough)
  • git skills (basically, how to commit changes, send them to our repos, dealing with branches without making a mess, etc)
    You can find some documentation about git at: http://git-scm.com/documentation

If you think you can cope with the requirements, then developing on Replicant should cause you no particular issue.

Writing free software replacements

Writing free software replacements for non-free components may require more skills depending on what you're trying to achieve, though there may be people with the adequate knowledge to help you and from whom you will likely learn a lot.

Repositories

When working with Replicant repos, make sure to avoid breaking things. For instance, if you push a commit introducing a compilation error, it will break the whole build process.
It is better to create separate branches (that are not used by the official manifest branches) when your work is still in progress.
Creating branches that add debug infos on a particular topic is usually a good idea since it will save you time next time you want to debug the same component.

When creating a repository

In order to keep repo naming consistent, please name repositories by their name on the tree, replacing the / by _.
For instance, when forking the CyanogenMod repo: android_device_samsung_crespo, rename it to device_samsung_crespo on the Replicant repos.
This creates a more consistent way of naming repositories and makes it easier when pushing: just look at the location in the source tree and replace / by _.

When creating a branch

Official replicant branches are named the following way:
  • The replicant- prefix
  • The Replicant version

Such as: replicant-2.3 This should be used on the projects repositories as well as the manifest repository.
Any other branch should be considered as Work In Progress (WIP) and thus not be part of any official branch of the manifest.

There is although one exception, with the master branch, that can be used by any project and be in any manifest given that the code held in the master branch will work on any Replicant version.

Upstreaming work

It is generally a good idea to send some changes back to upstream, assuming that they will benefit from it as well.

When it is about the replacement of a non-free component present in the upstream systems, make sure that your replacement is reliable and complete.
Contact the interested developers on the upstream projects before attempting to send your replacement.

CyanogenMod

The CyanogenMod team uses Gerrit to manage patch submissions. The process to get your patch included in CyanogenMod repos is explained on their wiki: Gerrit

You can push directly using git using the following scheme:

git push ssh://<sshusername>@review.cyanogenmod.org:29418/CyanogenMod/cm-kernel HEAD:refs/for/<branchname>

AOSP

The Android Open Source Project uses Gerrit to manage patch submissions. Some information about submitting patches to AOSP is available: http://source.android.com/source/submit-patches.html

You can push to AOSP's review using:

git push https://android-review.googlesource.com/platform/system/core HEAD:refs/for/master

Writing free software replacements

Here are some tips that may help you achieving a free software replacement for a specific component (some may be more or less relevant regarding the nature of what the component does):
  • Look for interested people from other projects: CyanogenMod people are constantly fighting with non-free blobs and are sometimes happy to help replacing one.
  • Use tools such as strings, objdump and radare2 against the non-free binary to have a better idea of how things work. (Make sure this is legal where you live!)
  • Try to make the non-free binary as verbose as possible by enabling all the possible debug options on the config file or such.
  • Run the program in strace and analyze the trace to understand what the program does.
  • Add verbose debug prints in the concerned kernel driver (with printk and show them via the dmesg tool).
  • Read the corresponding kernel driver: you can sometimes learn a lot by reading comments or headers.
  • Collect data out of the kernel driver (via debug prints) and out of the non-free binary (via debug prints on the upper-layer).
  • If there is a mathematical algorithm involved, force the values returned by the kernel to the non-free binary and analyze how it reacts, for instance with spreadsheet software.
  • If you're directly dealing with a hardware component, try to find a datasheet for the chip, it may hold precious details. In the best case, you may also be able to find a reference software implementation!

Wiki guidelines

In order the keep the wiki simple and consistent, a few guidelines must be followed when editing:

  • Every page in the wiki should be written in correct English, we do not aim to provide informations in any other language
  • Only Replicant-specific topics should be covered: there is no point in writing usage guides for generic Android aspects, such as the user interface
  • The content on each page must be relevant only to the latest Replicant version: make sure to update the content with newer Replicant versions
  • Follow the devices naming convention (the Galaxy S 3 (I9300) is not to be called Samsung S3 GT-I9300 or Galaxy S III)
  • Name the pages in a consistent manner (NexusSI902xFirmwares is not to be called FirmwaresOnTheI902xNexusS)

Commonly-used terminology

In order to keep everything clear and consistent, we use the following terms with a precise meaning in mind:
  • Driver: Software that is part of the kernel (builtin or as a module) and deals with communicating with the hardware
  • Hardware Abstraction Layer (HAL): Software that runs in user-space and deals with communicating with the hardware (usually through a kernel driver)
  • module: Android HALs are also often called modules, so we may referrer to e.g. the audio HAL as the audio module
  • blob: Proprietary HAL
  • firmware: Software that does not run on the main processor (the CPU) but rather in a separate chip (e.g. the Wi-Fi firmwares runs on the Wi-Fi chip)

New images release guide

1. Modify vendor/replicant/CHANGELOG.mkdn, commit and push
2. Update prebuilts (FDroid, Terminal Emulator, etc)
3. Start the build
4. Run the release script and ensure everything is OK
5. Compress the release files

tar -cjf 0005.tar.bz2 0005

6. Upload the release to ftp-osl.osuosl.org
scp -v 0005.tar.bz2 replicant@ftp-osl.osuosl.org:/home/replicant/data/images/replicant-2.3/0005.tar.bz2

7. Unpack the release, fix permissions
8. Modify ReplicantImages, last image on every devices page
9. Update ReplicantStatus with the latest status
10. Announce the release on the blog, mailing list
11. Update the IRC topic

New device documentation guide

1. Create the device main page, following the naming guidelines applied to other devices (e.g. the Samsung Galaxy S II GT-I9100 is called Galaxy S 2 (I9100) and its page is GalaxyS2I9100)
2. Create all the related sub-pages (build guide, install guide and firmwares list at least), following the naming guidelines applied to other devices (e.g. GalaxyS2I9100Build, GalaxyS2I9100Installation and GalaxyS2I9100Firmwares)
3. Link the sub-pages to the main page in the index
4. Update the ReplicantStatus page of the wiki with the current status of the device
5. Modify the WikiStart page of the wiki and add the new device in the following sections:

6. Add new issues categories to the Replicant project redmine


Wiki License: Creative Commons BY-SA