Building AOSP image

If your embedded product is a touchscreen device such as a Kiosk/Smart TV/infotainment System that relies upon a custom Linux OS then you may have faced challenges in hardware driver support and maintenance of regular software/security updates. Maintaining a custom-built Embedded Linux is a costly task and requires expertise in building the OS and reliably providing OTA updates. 

Over the years Embedded Android has evolved into a much better Alternative. Here in this post, I want to share the basic steps to start building an AOSP project from scratch. This will later help if someone wants to build/port a custom Embedded Android stack for a particular hardware

Here I will be sharing how I downloaded Android AOSP sources and built an AOSP image for a Nexus 7 [2012] device. You can follow this approach to build AOSP images for your devices, for example, Nexus 5. So Let’s Start.

Device Information 

The Tablet device used here is the Nexus 7 (2012)

• Product Name : grouper

• Variant: grouper

• HW version: ER3

• Bootloader Version: 4.23

Environment Setup 

>install some required packages

ayx@ayx-HP:~$ sudo apt-get install git-core gnupg flex bison gperf build-essential zip curl zlib1g-dev gcc-multilib g++-multilib libc6-dev-i386 lib32ncurses5-dev x11proto-core-dev libx11-dev lib32z-dev ccache libgl1-mesa-dev libxml2-utils xsltproc unzip

ayx@ayx-HP:~/$ sudo apt-get install ncurses-dev

> install adb tool

ayx@ayx-HP:~/$ sudo apt-get install android-tools-adb

> Fix Udev permission error 

ayx@ayx-HP:~$ lsusb

check the vendor id left of the colon, e.g nexus 5

Open this file 

ayx@ayx-HP:~$ sudo gedit /etc/udev/rules.d/51-android.rules

Put the following at the bottom of the file and save

# Nexus 5 Google Inc SUBSYSTEM=="usb", ATTR{idVendor}=="18d1", MODE="0666", GROUP="plugdev"

ayx@ayx-HP:~$ sudo chmod a+r /etc/udev/rules.d/51-android.rules ayx@ayx-HP:~$ sudo service udev restart ayx@ayx-HP:~$ fastboot -l devices ayx@ayx-HP:~$ sudo service udev restart ayx@ayx-HP:~$ sudo udevadm control --reload-rules ayx@ayx-HP:~$ sudo udevadm trigger ayx@ayx-HP:~$ fastboot -l devices

> install Java 7

ayx@ayx-HP:~$sudo apt-get install -f ayx@ayx-HP:~$sudo add-apt-repository ppa:openjdk-r/ppa ayx@ayx-HP:~$sudo apt-get update ayx@ayx-HP:~$sudo apt-get install openjdk-7-jre

select java 7 for the followings

ayx@ayx-HP:~$ sudo update-alternatives --config javac ayx@ayx-HP:~/$ sudo update-alternatives --config java ayx@ayx-HP:~/$ sudo update-alternatives --config javap

> Check versions of the following

In my cases, these were the versions 

gcc	5.4
Python	2.7
make	4.1
git	2.7.4
javac	7
java	7

> install repo tool

ayx@ayx-HP:~/$ mkdir ~/bin ayx@ayx-HP:~/$ PATH=~/bin:$PATH ayx@ayx-HP:~/$ curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo ayx@ayx-HP:~/$ chmod a+x ~/bin/repo

Download AOSP sources & Build Image  

> Download The Source

ayx@ayx-HP:~$mkdir ~/aosp_work ayx@ayx-HP:~$ cd aosp_work/ ayx@ayx-HP:~/aosp_work$ ulimit -S -n 1024

> Configure Git account

Replace “ ” marked text with yours  

ayx@ayx-HP:~$git config --global user.name "your_user_name" ayx@ayx-HP:~$git config --global user.email "your_mail"

> checkout Lollipop 

ayx@ayx-HP:~/aosp_work$ repo init -u https://android.googlesource.com/platform/manifest -b android-5.1.1_r1

ayx@ayx-HP:~/aosp_work$ repo sync -j4

Wait for the sources to be downloaded 

> Find your Device variant

ayx@ayx-HP:~/aosp_work$sudo adb devices ayx@ayx-HP:~/aosp_work$sudo adb reboot-bootloader ayx@ayx-HP:~/aosp_work$sudo fastboot oem unlock

Now in the FASTBOOT bootloader Mode, you will see the VARIANT and other device-related info printed, take note of those. THIS IS THE MOST IMPORTANT THING TO NOTICE

> Download The Device binaries

then go to https://developers.google.com/android/drivers And download the latest binaries for your variant, e.g. for GROUPER variant considering the OS version you want to build. Take note of the branch

extract the binaries to the root of the source tree. For our case into the “aosp_work” folder. Then extract them

> extract the binaries [press ENTER then Space then type I ACCEPT to accept license]

ayx@ayx-HP:~/aosp_work$ ./extract-asus-grouper.sh ayx@ayx-HP:~/aosp_work$ ./extract-broadcom-grouper.sh ayx@ayx-HP:~/aosp_work$ ./extract-elan-grouper.sh ayx@ayx-HP:~/aosp_work$ ./extract-invensense-grouper.sh ayx@ayx-HP:~/aosp_work$ ./extract-nvidia-grouper.sh ayx@ayx-HP:~/aosp_work$ ./extract-nxp-grouper.sh ayx@ayx-HP:~/aosp_work$ ./extract-widevine-grouper.sh

> setup cache for faster build

ayx@ayx-HP:~/aosp_work$ export USE_CCACHE=1 ayx@ayx-HP:~/aosp_work$ prebuilts/misc/linux-x86/ccache/ccache -M 100G ayx@ayx-HP:~/aosp_work$ echo 'export USE_CCACHE=1' >> ~/.bashrc ayx@ayx-HP:~/aosp_work$ . ~/.bashrc

> clean up

ayx@ayx-HP:~/aosp_work$ make clean ayx@ayx-HP:~/aosp_work$ make clobber

>Apply Patches  

There will be a build error related to “uniqueptr” , and you have to rebuild again, so it is better to first apply the patch, follow this Stackoverflow post to patch this issue 

ref: https://stackoverflow.com/questions/19186629/fatal-error-utils-uniqueptr-h-no-such-file-or-directory-error

ref: https://stackoverflow.com/questions/36048358/building-android-from-sources-unsupported-reloc-43

ref: https://groups.google.com/forum/#!topic/android-building/b66T0PzDIiM

> build

ayx@ayx-HP:~/aosp_work$ source build/envsetup.sh ayx@ayx-HP:~/aosp_work$ lunch

Choose “userdebug” option

ayx@ayx-HP:~/aosp_work$ make -j12

This build will use a prebuilt kernel from the vendor.

If everything is okay then the build will be successful 

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ESP32 Non Volatile Storage tutorial

 NVS stands for Non-volatile Storage 

This library is designed to store key-value pairs to flash 

By default The flash has an NVS partition at 0x9000 offset address, it contains the wifi data 

We will go through this example to make use of the NVS memory 

https://github.com/espressif/esp-idf/tree/master/examples/storage/nvs_rw_value

At first NVS partition is initialized, if there are no free pages then it is erased and re-initialized again 

// Initialize NVS     esp_err_t err = nvs_flash_init();     if (err == ESP_ERR_NVS_NO_FREE_PAGES || err == ESP_ERR_NVS_NEW_VERSION_FOUND) {         // NVS partition was truncated and needs to be erased         // Retry nvs_flash_init         ESP_ERROR_CHECK(nvs_flash_erase());         err = nvs_flash_init();     }     ESP_ERROR_CHECK( err );

Multiple internal ESP-IDF and 3rd Party apps can store key-value pairs in the NVS partition using this library. in order to reduce possible conflicts on key names, the library provides a way for the user to store values by creating Namespace first. 

* @param[in]   name        Namespace name. * @param[in]   open_mode   NVS_READWRITE or NVS_READONLY. * @param[out]  out_handle  If successful (return code is zero), handle will be returned esp_err_t nvs_open(                   const char* name,                   nvs_open_mode_t open_mode,                   nvs_handle_t *out_handle                   );

At first, create a handle to reference the further usage of NVS 

nvs_handle_t my_handle;

 

Then open the namespace 

err = nvs_open("storage", NVS_READWRITE, &my_handle);

To set/ save a value for a key use the following function 

* @param[in]  handle  Handle obtained from nvs_open function. * @param[in]  key     Key name. * @param[in]  value   The value to set. *                     For strings, the maximum length (including null character) is *                     4000 bytes. esp_err_t nvs_set_i32 (                       nvs_handle_t handle,                        const char* key,                        int32_t value                       );

After writing a value you must commit to ensuring changes are written to flash storage 

esp_err_t nvs_commit(nvs_handle_t handle);

To read from the key use the following function

* @param[in]     handle     Handle obtained from nvs_open function. * @param[in]     key        Key name. * @param          out_value  Pointer to the output value. esp_err_t nvs_get_i32 (nvs_handle_t handle, const char* key, int32_t* out_value);

After usage close the handle 

/** * @brief      Close the storage handle and free any allocated resources * * This function should be called for each handle opened with nvs_open once * the handle is not in use any more * * @param[in]  handle  Storage handle to close */ void nvs_close(nvs_handle_t handle);

Build and run the example on the ESP32 

The output of the program : 

Please take a look at the following snippet from Espressif. It has some important info on the partition 

Wrapping the NVS in, we can easily create a custom database library. I have designed a lot of databases on top of NVS. There are some design patterns that work by creating a cache in RAM thereby preventing excessive write cycles to NVS. this is also known as wear-leveling 

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