Android Device Configuration for Aosp

Android device configuration for AOSP

Right... So you want to build your own device tree, read on.

Disclaimer: this is by no means complete, and there will be omissions as have explained all this top of my head and copied pasted certain bits that I have here on my own device tree.

The device tree, for example, /device/lg/gt540would consist of the following make files:

• Android.mk - this will tell the build system to include and to build sources specifically for your device. See below, for an example. This is dependant on the device and hardware, you could have libsensors, liblights, libcamera subdirectories under the example device tree, i.e. /device/lg/gt540/libsensors, /device/lg/gt540/liblights, /device/lg/gt540/libcamera etc.
• AndroidBoard.mk - this is for the kernel, the build system uses that to drop the kernel image in place (more about this in a few minutes)
• AndroidProducts.mk - specifies the appropriate device's make file, to use for building. i.e. /device/lg/gt540/device_gt540.mk, this is specific also.
• device_xxxxx.mk - specifies the properties and extras to copy over into the final output, in this case, it could be for example, device_gt540.mk
• BoardConfig.mk - This is the meat of it all, this is where compiler conditional flags are set, partition layouts, boot addresses, ramdisk size, and so on.

Lets peek into each of those to give a glance as to where it all fits in.

Android.mk:

ifeq ($(TARGET_BOOTLOADER_BOARD_NAME),xxxxx)
    include $(call all-named-subdir-makefiles, recovery libsensors liblights libcamera ....)
endif

This is how the build will use that to build recovery, sensors, lights and camera (of course there will be more), its saying 'Yo Builder, go into each of the directories specified, and build the respective sources plskthxbai'

AndroidBoard.mk:

LOCAL_PATH := device/lg/gt540/

#
# Boot files
#
TARGET_PREBUILT_KERNEL := $(LOCAL_PATH)/kernel

file := $(INSTALLED_KERNEL_TARGET)
ALL_PREBUILT += $(file)
$(file): $(TARGET_PREBUILT_KERNEL) | $(ACP)
    $(transform-prebuilt-to-target)

Now this, is telling the build system, to be able to drop this kernel into the out/target/product/lg/gt540 (notice the correlation with the device tree directory?)

AndroidProducts.mk:

PRODUCT_MAKEFILES := \
    $(LOCAL_DIR)/device_gt540.mk 

Its telling the build as in 'Yo Builder, read that device make file please and process it upon completion of build.'

*device_xxxxx.mk: (for this example, device_gt540.mk) *

PRODUCT_NAME := lg_gt540
PRODUCT_DEVICE := gt540
PRODUCT_MODEL := LG GT 540

PRODUCT_COPY_FILES += \
    ... specific ...

PRODUCT_PROPERTY_OVERRIDES := \
    ro.com.android.dateformat=dd-MM-yyyy \
     ... more stuff ...

This is where all the specifics for the device such as drivers, proprietary libraries, supporting scripts specifically for the device, gets copied over to out/target/product/lg/gt540/system/ in this case. Notice how the overrides for the properties, these end up in the build.prop found in the root of the /system of the Android ROM.

BoardConfig.mk:

LOCAL_PATH:= $(call my-dir)

TARGET_NO_BOOTLOADER := true
TARGET_PREBUILT_KERNEL := device/lg/gt540/kernel
TARGET_PREBUILT_RECOVERY_KERNEL := device/lg/gt540/recovery_kernel

# This will vary from device!
TARGET_BOARD_PLATFORM := msm7k
TARGET_ARCH_VARIANT := armv6-vfp
TARGET_CPU_ABI := armeabi
TARGET_CPU_ABI := armeabi-v6l
TARGET_CPU_ABI2 := armeabi

# OpenGL drivers config file path
BOARD_EGL_CFG := device/lg/gt540/egl.cfg

# Dependant, not to be taken literally!
BOARD_GLOBAL_CFLAGS += -DHAVE_FM_RADIO

# Dependant, not to be taken literally!
BOARD_KERNEL_BASE := 0x02600000

# this will be device specific, and by doing cat /proc/mtd will give you the correct sizes
BOARD_BOOTIMAGE_PARTITION_SIZE     := 0x00480000
BOARD_RECOVERYIMAGE_PARTITION_SIZE := 0x00480000
BOARD_SYSTEMIMAGE_PARTITION_SIZE   := 0x0cf80000
BOARD_USERDATAIMAGE_PARTITION_SIZE := 0x0d020000
BOARD_FLASH_BLOCK_SIZE := 131072

That is an excerpt, notice how we specify kernel's base address, this is how the boot.img gets generated after compilation is done and yet again, gets dropped into out/target/product/lg/gt540/boot.img. Also, more importantly, we're telling the build system to use the target platform for cross-compiling the sources (*TARGET_BOARD_PLATFORM*/*TARGET_CPU_ABI*) There will be more information in there such as conditional flags to pass to the compiler, for an example. we specified the directive HAVE_FM_RADIO to tell it, when it comes to handling the source for the FM radio system, to conditionally compile parts of the source. Again, this is hardware specific and mileage will vary, also this applies to the address for boot. In a nutshell, this is saying 'Yo Builder, read the damn variables and remember them and apply them when cross-compiling those source files!'

Now that the internals of each of those Android build make-files are shown.

Now, onto the vendor/ part of it, in AOSP, simply, once again, correlation and corresponds with the device/ tree, as in continuing with this example, vendor/lg/gt540/ which gets picked up by the lunch. There's more make files in there but the general consensus is there's a directory called proprietary which contains the proprietary libs (due to close-source etc) that gets copied over. The copying over of the libraries gets specified in the file device-vendor-blobs.mk, in this case, gt540-vendor-blobs.mk.

When the magic happens by doing the following:

. build/envsetup.sh

This is reading in the entire entries found in each of the device/ subdirectories and "remembers them", so the build system knows what type of target is used etc.

When the . lunch gets invoked, a menu appears prompting to pick the device that is required to build. Now the last and final step to do the build...

make -j5 > buildlog.log 2>&1

I run multitail on another terminal and monitor the buildlog.log file to check and make sure its building.

This last step will depend on how many cores you have (n cores + 1 as a rule) and it takes a while to build, GB build takes 40mins on my laptop running Arch Linux 64bit, ICS build takes about 2hrs 30 mins. So mileage will vary on what type of horsepower your machine has.

When the build is done, a little bell goes off and at the bottom of the said log file, I see this:

Combining NOTICE files: out/target/product/xxxxx/obj/NOTICE.html
Target system fs image: out/target/product/xxxxx/obj/PACKAGING/systemimage_intermediates/system.img
Install system fs image: out/target/product/xxxxx/system.img
out/target/product/xxxx/system.img+ total size is 108776448

As matter of interest JBQ (Jean Baptiste Queru - the 'boss' for managing/distributing the source from Google), his build step is this...

make -j32 

Yup! 32 cores! That..... is pretty powerful.

What is the sweet spot PC configuration to download and build android AOSP (as of 2022)?

You can see the complete system requirements and recomendations at https://source.android.com/setup/build/requirements

• A 64-bit environment is required for Android 2.3.x (Gingerbread) and higher versions, including the master branch. You can compile older versions on 32-bit systems.
• At least 250GB of free disk space to check out the code and an extra 150 GB to build it. If you conduct multiple builds, you need additional space.
• At least 16 GB of available RAM is required, but Google recommends 64 GB.
  As of June 2021, Google is using 72-core machines with 64 GB of RAM internally, which take about 40 minutes for a full build (and just a few minutes for incremental builds, depending on exactly which files were modified). By contrast, a 6-core machine with a similar amount of RAM takes 3 hours.

Configure AOSP for a batteryless device?

As Simpl mentioned, AOSP describes how to configure batteryless devices,
I implemented health HAL for my industrial device on Android 9, by default with no battery it shows Battery UNKNOWN (as mentioned in AOSP documentation). My requirement was to show Battery 100% when no battery inserted and actual battery status when battery is present.

Below is the code snippet from my health hal, HealthService.cpp

int healthd_board_battery_update(struct android::BatteryProperties *props) {
    // return 0 to log periodic polled battery status to kernel log
    if (! props->batteryPresent){
    props->chargerAcOnline=true;
    props->batteryPresent = true;
    props->batteryStatus = android::BATTERY_STATUS_CHARGING;
    props->batteryHealth = android::BATTERY_HEALTH_GOOD;
    props->batteryFullCharge = 100;
    props->batteryLevel = 100;
    }
return 0;
    }
 

For more details on how to write your own health HAL, follow:
https://android.googlesource.com/platform/hardware/interfaces/+/master/health/2.0/README.md

How can I add individual settings to Android System settings?

How can I add individual settings additional to Android system settings?

By building a custom Android image and changing the settings app at packages/apps/Settings/src/com/android/settings.

Porting AOSP to specific hardware device

1. The adb rules are to enable adb to work over USB. If you can connect to your device over ADB then the adb rules worked. You may have to enable ADB in the device's Developer Settings.
2. After you have synced AOSP you can build for your device. You can choose your device in the lunch menu. Run the build/setenv.sh script. Then run lunch. It will have a list of specific devices you can choose from. You can add to that list by syncing new device trees into the tree.
3. By default it will build system.imgs that you flash through fastboot. If you are building AOSP, make otapackage will make a flashable zip.
4. The build will make an emulator image that you can test by running emulator. That will give you a general idea of if your build works, but will not give you the full story with regards to your specific device. For instance, the emulator build might run but if you forgot to add the correct proprietary files the build might not boot on your specific device. But you are very unlikely to hard brick your device by flashing a system.img.

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