How open is the source code of android phones? I cannot think of a way that manufacturers can close their drivers, because they have to conform to the GPLv2 as the License of the Linux kernel states. Or do they use write a large part in user space code, where they can choose their own licence?
The information I'm trying to get here is: How difficult is it to get a "cheap" smartphone (htc wildfire-s) and run Linux on top of it full featured. What I mean is every hardware feature is easily accesible without having to implement your own drivers and reverse engineer the device (assuming that the device is rooted).
HTC has the developers area:
http://htcdev.com/devcenter
The kernel sources for the HTC wildfire you can also download there:
http://htcdev.com/devcenter/downloads
Note that not all the functionality is included in the kernel. To add functionality to your system you also have to install basic programs like a shell.
The Android system image already contains all necesary programs to run your system and som Android stuff which is not needed for a Linux-only system.
As an alternative you can have a look in the android source and remove all the unwanted programs from your custom android build.
http://source.android.com/source/initializing.html
I think I found my answer at last. A lot of firmware of a lot of android phones is delivered binary only. Which makes it less open. If I want to run GNU/Linux on top of a stock phone I run in a lot of those issues. See Richard Stallmans article on how free android is:
Is Android really free software?
There is also a project Replicant which tries to create a free (FSF definition of free) android based stack.
Related
I want to modify the system apps running on my specific phone. I am stumped about some important steps on how to do that - see my questions further below.
N.B.: I am not interested in deploying these modifications to other phones. Instead I want to play with the original code and improve it. Hence "create your own system app" is no sufficient answer.
Background
I am just starting to get into Android development (have sufficient Java knowledge, though). There are plenty of great tutorials out there (e.g. here and here) but they all seem to cover user application development. I'm more interested in getting (a little) "closer to the metal". Unfortunately I am unable to find good sources teaching how to do that.
Example
As an example let's say I want to modify how the built-in brightness control works (e.g. changing the minimum) or want to add features to the call screen (e.g. "Send SMS instead" when the line is busy).
Specific Questions
I obviously need these things to get started...
Sources
The sources for (parts of?) the OS running on my phone. This is the part that confuses me the most. Can I just download the official sources or is it likely that my vendor made modifications?
In my specific scenario (I use a Fairphone), could those modifications be contained in any of these sources:
some core apps deployed by the vendor
the image binaries (some way down the page)
sources for the Linux kernel and some other libraries
Tools
I really hope to stay in Java-land. But either case I need a development (I hope to use Android Studio or Eclipse ADT) and a debugging environment (I hope the Android Virtual Devices suffice).
Is it a valid assumption that I can use those tools for system apps or are they usually implemented in C?
Process
Assuming I can download the official sources and get started with, e.g. Android Studio. As opposed to developing a user app, do I have to do anything special to emulate the modified system app on AVD?
I'm asking because I assume that AVD already runs an unmodified version of that very app.
I am just starting to get into Android development (have sufficient Java knowledge, though). ... I'm more interested in getting (a little) "closer to the metal".
You can of course follow your own bliss, but you may find it pretty frustrating to learn Android development by hacking on the OS itself. You'll find yourself doing a lot of OS debugging and working with harder-to-use tools than normal.
Example
As an example let's say I want to modify how the built-in brightness control works (e.g. changing the minimum)
I realize this is just an example, but this could be a tough one, because there are a lot of things that contribute to brightness control -- there's the app with the UI that sets it, but that talks to the framework and ultimately the driver for the hardware that actually deals with brightness curves for the display, in coordination with the ambient light sensor.
or want to add features to the call screen (e.g. "Send SMS instead" when the line is busy).
There's a dialer app, but implementing a feature like that will be...difficult, provided it's even feasible. I don't know offhand whether that sort of call state is available to the API.
Specific Questions
I obviously need these things to get started...
Sources
The sources for (parts of?) the OS running on my phone. This is the part that confuses me the most. Can I just download the official sources or is it likely that my vendor made modifications?
If you're replacing system apps, you'll need to run an OS signed with debug keys; you don't have access to the signing keys for the installed system apps on a retail build of the OS that would enable you to replace them. That will mean either getting a debug-keys installation or building it yourself from source, and flashing it to your phone. I would most strongly discourage you from using your daily phone for this sort of work -- you don't want it to be bricked when you need to receive an important call.
If you're not running a Nexus phone, then yes, your vendor has made modifications. The system apps are probably modified, and you almost certainly won't have access to the closed source of those apps. Also, there will be closed-source device drivers that are essential to the operation of the OS that you won't have access to. If you're trying to get AOSP Android up and running on such a device, as an individual hacker it's at best very, very difficult. If you're willing to use something like CyanogenMod, you could look to see if (and to what extent) they support your hardware.
If you are running a Nexus phone, then it's a goal of the AOSP project to try to have the OS bootable on select Nexus devices, though you won't necessarily enjoy the fullest functionality of the retail OS build, depending on the state of drivers -- even Nexus phones can have closed-source drivers and bits that make life more, um, exciting for building with AOSP.
In my specific scenario (I use a Fairphone), could those modifications be contained in any of these sources:
some core apps deployed by the vendor
Almost certainly
the image binaries (some way down the page)
Not sure what you mean by that
sources for the Linux kernel and some other libraries
It's unlikely there are significant modifications to the kernel itself, though vendors sometimes do...interesting...things with system configuration. I already mentioned device drivers. Vendors also have custom implementations/modifications of some framework APIs.
Tools
Vendor-specific tools are rare.
I really hope to stay in Java-land. But either case I need a development (I hope to use Android Studio or Eclipse ADT) and a debugging environment (I hope the Android Virtual Devices suffice).
Much of what you want to do can probably be implemented in Java, though it depends on how close you're getting to the hardware which can be difficult to know.
Is it a valid assumption that I can use those tools for system apps or are they usually implemented in C?
The "system apps" are implemented in Java, but again, you sort of have to know where the dividing line is.
Process
Assuming I can download the official sources and get started with, e.g. Android Studio. As opposed to developing a user app, do I have to do anything special to emulate the modified system app on AVD?
That's actually different, because you're dealing with an emulator system image instead of a phone image. The emulator system images are completely open source, and you can build them from AOSP.
I'm asking because I assume that AVD already runs an unmodified version of that very app.
That's correct.
To come back to my initial point, if you read between the lines of what I'm saying, I won't tell you it's impossible, but the difficulty ranges from freakin' tough on the easy end to spend-years-of-your-life on the hard end. If you really want to proceed, your best bet may be to buy the phone that's best supported by CyanogenMod and work that angle; there's a more active developer community there to help you. I know you're more excited about trying to customize the OS than you are in making a user-space app, but you'll experience less frustration with the latter than the former.
During my education I have been developing Android iOS apps and websites for almost 18 months. Now, as my final year project, I am working on Linux source code with the goal to boot it on a mobile device – like Android. I have it successfully as a Debian package following tutorials on the Internet. I am currently using Ubuntu.
I have a strategy but not sure if I am on the right track. It is as follows:
A:
Download Linux source code. Remove extra drivers, compile and
install it on currently running Ubuntu and use it.
Customize the code further and boot it as my own distribution. For
that I'm following LFS.
Specify a particular target mobile, modify the code for it, write
drivers if I need any, not sure which one (that's why I'm here :) ),
and boot the kernel on it.
I do not know whether my strategy is right or not. I'll really appreciate if someone can tell me:
B:
Am I on the right track? If not, what might be the right one?
Do I need to specify a mobile and customize the kernel code for that
one?
Other than drivers, what else do I need to change in the kernel?
Last but not the least when I boot the kernel on a mobile device; am I going to have any
interface or terminal there?
Sorry if my question doesn't make sense. I am a student and still trying to figure things out. I would be very thankful if someone could give me hints on what subjects to search for on the Internet.
Update: What I want is to confirm whether my strategy is correct or not. If not, then please just name the steps I should follow.
It is not unusual that the drivers for the SoC and devices around it are closed source.
As far as I know, the drivers for the Exynos SoC (the stuff Samsung uses in many of their devices) is (partly) closed source.
So generally speaking you have to write drivers for everything and everyone.
Especially the actual radio connection is tricky as there are no devices which need proprietary
firmware blobs (although the rest of the drivers may be open source).
Another problem is the boot loader on many devices, which does not easily let you install
custom kernels (hash sum stored in the boot loader, unwilling to boot if kernel hash does not
match).
So, assuming you are developing for a device that is already supported by android, I personally
would start with the corresponding device tree for your device and start modifying that.
You can a lot of device trees on CyanogenMod's github page.
Benefits:
You can start off with a working state
If something breaks you know it was you
Alternatively, you can peek at other projects like Ubuntu Touch.
They are able to utilize existing android kernels by using Hybris.
If you want to have a distribution based on Debian/Ubuntu I would recommend
trying Ubuntu Touch and modifying that.
I hope this is the right place to ask this.
I would like to work on an Android build with a completely custom OS. I was inspired by this project that ported Inferno to Android.
I would like to do this legally (obeying all terms of service and what-not) if possible, and I have no problem with disclosing my source code to a carrier.
Do any of you have experience with this? What are the considerations for getting a custom build to work with a carrier?
Since I am building on Android, I probably won't have to worry about cell/3g/4g hardware drivers, and I would like to buy a phone from the carrier anyway just to make sure it will be supportable.
I'm one of the creators of the Inferno project you mentioned. Anyway, making a completely custom OS for an Android phone will be difficult; a lot of the hardware will be undocumented or only drivable by Linux binary blobs. What we did (and what Boeing has also done recently for a commercial project) is strip away all the Java from an Android system, leaving a basic Linux upon which you can build your own custom interface. This lets you use all the hardware (since the drivers are in Linux), but everything that the end users see will be your stuff. There are a variety of ways to go from there. Inferno implements a virtual machine, so we can abstract the Linux stuff into our own Inferno-style world.
I don't think there should be any problems with the carriers. We started with a Cyanogenmod ROM and hacked on that; custom ROMs are just fine! I never had any problems, even when I was swapping my little pay-as-you-go SIM card among several phones running Gingerbread, ICS, and Inferno.
Head over to the AOSP source, and clone it. Strip out what you don't need in your branch and begin the kernel patching! You'll need to modify the kernel in portions to make it compatible (fairly) with the device you're on. The Android kernel is in fact a very close cousin of the Linux Kernel, and in Linux 3.3, they've begun merging the two. After this is done, write your interfacing mechanisms (be it a display, web interface, etc) and you can test it out on your platform.
I own a Samsung Galaxy 3 and want to port kernels available for other Android Devices. I have all building environment ready. I have C knowledge also. What exactly I dont understand is how and what all things porting involves, which codes should be modified in what way?
If someone could help me. It would be great.
Thanks in advance.
Ok I got it. But the real problem is I dont understand one thing.
What needs to be changed in the source code so that to make it compatible in other device? Can someone explain me that?
Idolon gives a good suggestion. In theory what is written there is true. In practice, it's a little more involving. I've been porting Android Kernel for months now. My goal was to have a custom S5PV210 processor module on my custom board with my custom I/O. I have the source code for Samsung's galaxy tab and several Samsung's android smartphone as well as a few versions (Froyo, Gingerbread) for the Samsung's Evaluation board (SMDKV210 for S5PV210 CPU). FYI, S5PC110 is a close derivative. Here is what I found out.
Eventhough all the device drivers are supposed to be built in a very modular way and independent from each other and you should be able to replace them with similar devices, the way Samsung did it is not exactly that. To give you one example is about power management. In many low level drivers dealing with hardware devices, it calls some specific routine for other hardware devices like power management chip. So, When you change the choice of drivers in the "make xconfig" or "make menuconfig" it will remove the source code of what you don't want and add the one you want but, there are still other modules that are calling the low level function you removed. When building, you will get tons of unresolved external because you removed a power management chip that your hardware doesn't have but is used in the source you started with. I looked through several Samsung's device source code and they have branched very early on. They have been adapted by different teams and it would be a major amount of work to go from one device to the other from one source kit.
Here is how I succeeded: I bought an S5PV210 evaluation board with an already ported Android Kernel (Gingerbread). All the power management and inter dependant issues where already cleaned-up. Then, form a working kit, I could change the device I needed (the one you can't buy without a 100K unit/yr commitment) without getting stuck with the interdependancy. Then I could even change LCD resolution (from 800x480 to 1024x768), touchscreen, Cell modem etc etc. The whole thing takes about a month worth of work with only one guy (me).
Starting with a Galaxytab or other commercial device made me waste months of headakes with no useful results but the thing I've learned.
There is one requirement to succeed on my approach. You have to know the hardware you are working on. As an example, you need to know what touch screen your hardware has (chipset) to select the driver and were is it connected to hook it up to the right device (USB, Serial etc). That the same thing for all other devices (power managemnt chip, keypad, backlight, LCD etc etc)
Hope that is useful to give you an idea of the work involved and how you can do it.
You should take a look at the cached copy of Android Platform Developer's Guide and at android-porting google group.
There is also an old but useful article about porting Android to Nokia N810, which will give you some hints about Android Linux kernel porting.
I am also into android porting stuff for quite some time I suggest the following route :
Read
You need to have basic knowledge of android porting and AOSP source code, directory stucture hierarchy.
I suggest you to start reading https://books.google.co.in/books/about/Embedded_Android.html?id=plHsngEACAAJ&hl=en
and also refer https://source.android.com/devices/index.html as good guys pointed out you can also google android porting related groups and become a member there, if you are stuck on a issue there are chances similar issue might have been faced by someone else previously.
Observe
AOSP code :
Parallely you need to dive in to the android source e.g from links like https://android.googlesource.com/ observe which components are placed where in the source code, what are the updates from previous android release (like ART replaced dalvik in LL), at top level there would be generic code, code specific to your hardware called HAL in hardware/ and device/ folder.
Kernel code :
In the kernel also you need to observe the directory structure and know which things lie where like SoC specific code will be in arch/ directory defconfigs (used for selecting kernel configuration) will be arch//configs/ directory.
Also there are good books available for linux kernel, you can google them and start reading them also.
While porting kernel you need to take care of following
1.If in the new kernel there is already support of SoC which is used in hardware to be ported then you need to add only device specific changes like suppose you want to port new kernel version to samsung galaxy s3, you can take a reference android kernel having exynos support and then you need to make changes only for adding support for samsung galaxy s3.
For that you need to have reference of some old kernel having support of s3, from there you can study patches which have been added to add support for s3 and port those patches to newer kernel.
Experiment
First you can only port the bare minimum changes required to up the platform, compile and flash it on your platform, then observe the output, if everything looks fine than go on for next changes otherwise try to solve the issue.
Thanks,
Devarsh
I have a Symbian based phone with a ARM Cortex-A8 processor (SonyEricsson Vivaz) and was thinking on how hard would it be to try and port the Android OS for it. Obviously Android runs on a myriad of devices with different hardware so I imagine it shouldn't be too hard to adapt it to SE hardware. Could some one give me a clue where to start or if this is even undertakable...
How much information do you have about the hardware in the phone ? Are you starting completely from scratch ?
Porting Android is not simple task. First thing is to have Linux running (preferably 2.6.32 for more compatibility with the latest releases of AOSP.
If you can find a kernel that can run on your phone, that's one big step. After that, you want make sure that the peripherals you want to use also have the right drivers : touch interface, LCD display, SD card, audio, video. The ones that are probably most difficult will be wifi, radio (GSM) and power management module.
If you get that far, you don't have that much to go anymore, a few more changes in the kernel needed for Android, be able to compile Android correctly file system, hook up a few things like buttons and correctly interface with the drivers mentioned above...
But overall, definitely not an easy task (IMHO).