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Android 6 Marshmallow over Network File System (NFS) on the Wandboard

This tutorial assumes you have already built and deployed Android 6.0.1 for the Wandboard on an SD-card, according to our preceeding blog post in this series. For quick reference, we are using the Android source 6.0.1 for the Wandboard from the official website. The source code is assumed to be extracted to /opt/android/wand, and our host system is Ubuntu 16.04.

Android system development on an SD-card can be quite cumbersome. Even though there is the possibility of pushing and pulling files via Android Debug Bridge (ADB) between the target device and the host computer, more often than not, you still need to replace the contents of the SD-card manually. In the following, we will show you how you can boot the Linux kernel via TFTP and the Android operating system over NFS.

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Building and Deploying Vanilla/AOSP Android 4.4.4 for the Wandboard

In this post we are going to build and deploy Android Kitkat for the Wandboard Quad. The instructions are mostly identical for the Wandboard Dual, although you will need a different u-boot bootloader configuration, and a different dtb file. With the current Android 4.4.4 build we are able to use ethernet, wifi in client and AP mode, as well as ALSA sound. Bluetooth and hardware accelerated graphics is not yet accomplished.

  • Host Build System: Ubuntu 13.10 (64 Bit)
    It is important to use a 64 Bit version, otherwise, it is not possible to build Android.
  • Hardware: Wandboard Quad revision B1
  • Kernel version: 3.16 rc5
    We will use the latest kernel provided by Robert Nelson
  • Bootloader: u-boot bootloader by Denx
    We will also download and patch as per instructions provided by Robert Nelson.
  • Android version: 4.4.4_r1 AOSP
  • An USB to serial converter for communicating with the Wandboard
    Unless your computer has a serial port of course.
  • A microSD card
    We recommend at least class 10, it really makes a big difference. A size of 2GB should be enough.

For this tutorial, we will have 3 main source code repositories, namely Android, u-boot and Linux kernel sources. It is assumed that we download the Android source code, and place the u-boot and Kernel sources in their respective sub-folders “u-boot” and “armv7-multiplatform” inside the Android source‘s root. While the exact location does not matter, we will use /opt/android as an example here. Since we are going to use a cross-compiler from Android for building the bootloader, it makes sense to first download all the source code repositories before starting with this tutorial.

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Cross compiling Android’s adb and fastboot for embedded Linux (e.g. Yocto/OpenEmbedded)

The tools adb and fastboot are essential for debugging, managing and customizing Android devices. Both adb and fastboot are available for download within the ADT Bundle, however, those prebuilt binaries are for common host platforms (x86 and x86_64). What if you would like to run adb on a different architecture, such as ARM? There are of course multiple ways to get this done. Here we will show you how to cross compile adb and fastboot outside of the Android source tree using a standalone Makefile.

For this tutorial you will need

  • A cross compilation toolchain
    We will be using the official yocto project toolchain
  • Source files for adb and fastboot
    These will be in the platform/system/core and platform/system/extras repository from the official Android sources
  • Source files of three “external” projects
    Namely zlib, openssl and libselinux, which are also available from the official Android sources

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Working with GPIO on the Wandboard and Writing an Android Driver for GPIO Interrupts

Following up on the last post “How to get started with Embedded Android on the Wandboard”, this article shows how to use the GPIO Pins of the Wandboard. It is based on the Android setup, however the generic part should run under other Linux based systems as well.

Finding the right GPIO Pin Number

In the userspace you are able to access GPIO functionality through the sysclass interface.

root@android:/ # ll /sys/class/gpio/                                           
--w------- root     root         4096 2013-06-20 10:57 export
lrwxrwxrwx root     root              2013-06-20 10:57 gpio101 -> ../../devices/virtual/gpio/gpio101
lrwxrwxrwx root     root              2013-06-20 10:57 gpio200 -> ../../devices/virtual/gpio/gpio200
lrwxrwxrwx root     root              2013-06-20 10:57 gpio24 -> ../../devices/virtual/gpio/gpio24
lrwxrwxrwx root     root              2013-06-20 10:57 gpio72 -> ../../devices/virtual/gpio/gpio72
lrwxrwxrwx root     root              2013-06-20 10:57 gpio75 -> ../../devices/virtual/gpio/gpio75
lrwxrwxrwx root     root              2013-06-20 10:57 gpio90 -> ../../devices/virtual/gpio/gpio90
lrwxrwxrwx root     root              2013-06-20 10:57 gpio91 -> ../../devices/virtual/gpio/gpio91
lrwxrwxrwx root     root              2013-06-20 10:57 gpiochip0 -> ../../devices/virtual/gpio/gpiochip0
lrwxrwxrwx root     root              2013-06-20 10:57 gpiochip128 -> ../../devices/virtual/gpio/gpiochip128
lrwxrwxrwx root     root              2013-06-20 10:57 gpiochip160 -> ../../devices/virtual/gpio/gpiochip160
lrwxrwxrwx root     root              2013-06-20 10:57 gpiochip192 -> ../../devices/virtual/gpio/gpiochip192
lrwxrwxrwx root     root              2013-06-20 10:57 gpiochip32 -> ../../devices/virtual/gpio/gpiochip32
lrwxrwxrwx root     root              2013-06-20 10:57 gpiochip64 -> ../../devices/virtual/gpio/gpiochip64
lrwxrwxrwx root     root              2013-06-20 10:57 gpiochip96 -> ../../devices/virtual/gpio/gpiochip96
--w------- root     root         4096 2013-06-20 10:57 unexport

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