LineageOS 14.1 build guide for the Samsung Galaxy Tab A 7.0 LTE 2016 (SM-T285)

This is a build guide specifically for the Samsung Galaxy Tab A 7.0 LTE 2016 (SM-T285) also known internally and for this guide as the gtexslte Note that the build is not compatible with the wifi only version also known as the gtexswifi or the (SM-T280)

Operating system and build environment that I used is

OS: Ubuntu 18.04 Processor: Ryzen 3 1300x with 16GB DDR4 ram

You do not need this exact hardware but I am including it for reference purposes. It may be possible to use another linux distro other than ubuntu however this guide will not cover that.

On the hardware front you do need a lot of disk space, when I mean a lot, I mean 100GB+, you will need to be storing the sources as well as the compiled binaries and intermediate code. You may also need to store the ROM image which takes at least a gigabyte each

We also have instructions on how to build firmware using Docker. Using Docker allows everyone to have a consitent build environment which would make support and debugging easier, aslo it allows for consistent builds even amoung different operating systems. As of November 2023, this instruction is the most complete and up-to-date.

Update Ubuntu

sudo apt install bc bison build-essential ccache curl flex g++-multilib gcc-multilib git gnupg gperf imagemagick lib32ncurses5-dev lib32readline-dev lib32z1-dev liblz4-tool libncurses5-dev libsdl1.2-dev libssl-dev libwxgtk3.0-dev libxml2 libxml2-utils lzop pngcrush rsync schedtool squashfs-tools xsltproc zip zlib1g-dev
sudo apt install openjdk-8-jdk
mkdir -p ~/bin

Here we prepare our working directory which will be at ~/android/lineage you can change this, but make sure to account for this change with respect to the instructions from this guide

mkdir -p ~/android/lineage
curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo
chmod a+x ~/bin/repo

Download sources

depth=1 and -c options to limit download size, you can omit this if you plan to work on android versions and have the time, internet speed and storage to handle this. However if your goal is just to be able to build lineage 14.1 from source for the gtexslte this is all you need

cd ~/android/lineage
repo init -u https://github.com/jedld/android.git -b cm-14.1 --depth=1
repo sync -c

repo sync will take a while, more like several hours depending on you internet speed. After it is finished you should be able to see the android project files in the current folder. If there are connection issues or failures you always execute repo sync again

Start Build

For Ubuntu 18.04, need to do this first to prevent "Assertion `cnt < (sizeof (_nl_value_type_LC_TIME) / sizeof (_nl_value_type_LC_TIME[0]))' failed" errors

export LC_ALL=C

Setup environment and also make commands like brunch work:

source build/envsetup.sh

Make sure you have enough space on your drive and then start the build. This will take some time, so be patient:

brunch gtexslte

If there are no errors, built intermediate code and binaries will be placed in the out folder. This includes binaries for the host machine (x86) and the device (arm)

You can find the images under out/target/product/gtexslte

adb and the other android commandline tools should also be available, make sure to add them to your path, for example:

export PATH=/home/jedld/android/lineage/out/host/linux-x86/bin:$PATH

This should take effect for a new terminal, you can do:

source ~/.bashrc

so that it takes effect on the current terminal

Building the kernel

There are still issues with the kernel build integrated into the LineageOS 14.1 build, so you may have to build it again to make it boot properly.

First we create a softlink since there are some paths that the kernel build script expects. Replace ~/android/lineage with the location of where your lineage project folder is.

ln -sf ~/android/lineage ~/android-work

Start the kernel build

cd ~/android/lineage/kernel/gtexslte
./build_kernel.sh

After the compile finishes, a new kernel should be built:

kernel/samsung/gtexslte/arch/arm/boot/zImage

Note: If you want to recompile or do a clean build you can do below

make mrproper

You also have to do the above if you want to start a new lineageos build via brunch

Creating the boot image

Now we have to create the boot image. Note that everytime you want to update the kernel you have to do both the kernel build and the boot image build.

Optional (enable adb on boot)

This is optional, but it may be useful to enable adb logging by default on the device so that you can get logs on first clean boot without going to developer mode.

First edit ~/android/lineage/out/target/product/gtexslte/root/default.prop and at the top of the file you will see this:

#
# ADDITIONAL_DEFAULT_PROPERTIES
#
ro.adb.secure=1
ro.device.cache_dir=/cache
ro.secure=1

change the secure bits to 0 like this

#
# ADDITIONAL_DEFAULT_PROPERTIES
#
ro.adb.secure=0
ro.device.cache_dir=/cache
ro.secure=0

This settings will be included in the boot image that will be built in the next step. Note that default.prop changes will require a reflash of the boot image everytime.

boot image creation (cont.)

Before starting this make sure that you have paths setup described earlier so that the mkbootfs command is available to you

mkbootfs ~/android/lineage/out/target/product/gtexslte/root | minigzip > /tmp/boot.img-ramdisk-new.gz

degas-mkbootimg -o ~/android/lineage/out/target/product/gtexslte/boot.img --base 0 --pagesize 2048 \
  --kernel ~/android/lineage/kernel/samsung/gtexslte/arch/arm/boot/zImage --cmdline "console=ttyS1,115200n8" \
  --ramdisk /tmp/boot.img-ramdisk-new.gz --dt ~/android/lineage/kernel/samsung/gtexslte/dt.img \
  --signature ~/android/lineage/device/samsung/gtexslte/seandroid.img

After this completes you should have a boot.img ready for flashing. This overwrites the image found in ~/android/lineage/out/target/product/gtexslte

Build Heimdall

We will use heimdall to flash our gtexslte

git clone https://gitlab.com/BenjaminDobell/Heimdall.git
sudo apt install build-essential cmake zlib1g-dev qt5-default libusb-1.0-0-dev

Go to the Heimdall folder and do the following:

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make
sudo make install

the heimdall command should now be available

Flash the boot image

Make sure your tablet is fully charged and it is OEM unlocked. (Disable OEM lock by going to Developer Settings)

First if you haven't done so, flash TWRP first:

https://forum.xda-developers.com/galaxy-tab-a/development/recovery-samsung-galaxy-tab-a6-sm-t280-t3475381

TWRP will be useful for wiping your device and flashing gapps later on. If you are coming from another ROM or stock, it might be wise to wipe your device first.

First make sure you are in the correct folder:

cd ~/android/lineage/out/target/product/gtexslte/

Then start the flash

heimdall flash --KERNEL boot.img --no-reboot

The flash will complete although it will just stop and an error will appear, but ignore this and go back to download mode again by holding power + HOME + VOL DOWN

Flash the system image

heimdall flash --SYSTEM system.img

Your system should automatically reboot and you should see the LineageOS startup logo instead of the samsung one.

Troubleshooting

If you did the default.prop edit, you should be able to use adb to check for boot problems. If not you have to go and enable developer mode on your device.

Now, if this is your first time to setup adb you may first need to fix permissions:

sudo vim /etc/udev/rules.d/51-android.rules

For the contents, you can paste the one found here https://github.com/M0Rf30/android-udev-rules/blob/master/51-android.rules

it is updated regularly even for other devices, then restart services so that it takes effect:

sudo chmod a+r /etc/udev/rules.d/51-android.rules
sudo udevadm control --reload-rules
sudo service udev restart

After this you can now do:

adb logcat

If you need a shell you can do:

adb shell

This will allow you to login to the device to explore the filesystem, execute commands and other things

MISC: building specific modules

You may have fixed a bug or made changes to the lineageos source code, and you want to deploy it to your device. For the most part if the changes only require an update to the system partition an image flash is not necessary.

First compile the module that you made changes with, for example changes where made to the gralloc module:

cd ~/android/lineage/hardware/sprd/gralloc
mm

The mm commmand will compile the current module and place the necessary compiled binaries to ~/android/lineage/out/target/product/gtexslte/system/lib

sync updated files to your device

Your devices system folder is readonly by default, we need to make it read/write:

adb root
adb remount

Note: You have to do this everytime your devices is restarted

You can now do this:

adb sync system

All modified files will be copied directly to your device system partition. Changes should take effect once you reboot your device.

MISC: Creating an Odin flashable zip

You might want to share your build, you can create an ODIN flashable package using this script below:

export BUILD=20181117
cd ~/android/lineage/out/target/product/gtexslte/
rm *.tar
rm *.zip
tar -H ustar -c boot.img system.img > LINEAGE-OMS-14.1-$BUILD-UNOFFICIAL-SMT285-ALPHA.tar
md5sum -t LINEAGE-OMS-14.1-$BUILD-UNOFFICIAL-SMT285-ALPHA.tar >> LINEAGE-OMS-14.1-$BUILD-UNOFFICIAL-SMT285-ALPHA.tar
mv LINEAGE-OMS-14.1-$BUILD-UNOFFICIAL-SMT285-ALPHA.tar LINEAGE-OMS-14.1-$BUILD-UNOFFICIAL-SMT285-ALPHA.tar.md5
gzip -c LINEAGE-OMS-14.1-$BUILD-UNOFFICIAL-SMT285-ALPHA.tar.md5 > LINEAGE-OMS-14.1-$BUILD-UNOFFICIAL-SMT285-ALPHA.zip

This will create a zip file that you can share on xda for example.

Contribution

If you would like to contribute to this guide or report any issues, simple do a pull request or file an issue at https://github.com/lineage-gtexslte/build_guide