How to populate boards for Android

Applicable for

This article describes how to load Android^TM distribution images, built for the STM32MPU, to defined Flash device partitions. It is intended for Distribution Package users.

1. Prerequisites[edit source]

The recommended host PC setup is specified in the following article: PC prerequisites.

The environment must be installed using the Distribution Package adapted to the selected microprocessor device.

It is assumed that:

STM32CubeProgrammer tool has been installed (refer to STM32CubeProgrammer)
OpenSTDroid distribution has been built (refer to How to build OpenSTDroid distribution)

Additionally, Fastboot mode is useful to accelerate the device provisioning (commands sent through USB).

In Linux environments, the Android USB drivers are built-in. The only action required is to set the target device information.

Information

To perform this action, you need administrator rights. In addition, you may need to add sudo in front of each executed command

To do this, open a terminal and

Create (or update if it already exists) the 51-android.rules file in /etc/udev/rules.d/ with the following information
- idVendor = 0483 (STMicroelectronics vendor)
- idProduct = 5720 or 0afb (depends on board configuration)
- Mode = 0660 (read/write permissions)
- Group = plugdev (Unix group which owns the device node)

Information

Check if you belong to the plugdev group by executing the following command:

$ groups

Example:

# Fastboot on STMicroelectronics devices
SUBSYSTEM=="usb", ATTR{idVendor}=="0483", ATTR{idProduct}=="0afb", MODE="0660", GROUP="plugdev"
SUBSYSTEM=="usb", ATTR{idVendor}=="0483", ATTR{idProduct}=="5720", MODE="0660", GROUP="plugdev"

Make sure that the access rights to the created file are the correct ones:

 chmod a+r /etc/udev/rules.d/51-android.rules

At this stage, your USB driver is correctly installed and configured.

2. Populate a board[edit source]

The out/target/product/<BoardId> directory contains all images built for the selected board during the setup (lunch step).

The STM32CubeProgrammer tool is used to flash the first stages of the images to the board. Then fastboot is used to flash the remaining images.

The board shall be started in "Forced USB boot for flashing" mode (also named DFU), selecting it through boot switches as explained in the article <your board reference - hardware description>, chapter Boot related switches (for example, Boot switches on the STM32MP257x-EV1 board for the STM32MP257F-EV1 board).

Connect the board to the host PC through USB.

The board can be designed to support several flash devices, for example: microSD, eMMC and so on. This document uses the eMMC as the Flash device example for this article.

Go to the distribution root directory, and run flash-device:

 flash-device

Once the DFU flashing is completed, the boot switches must be configured so that the correct Flash device (e.g. eMMC) is selected as the boot source.

Press the reset button and keep the USER 1 button (refer to LEDs and buttons on STM32 MPU boards) pressed until the board enters fastboot. The device provisioning continues until the required images have been loaded.

This operation takes several minutes.

When the download is finished, press the reset button in the board. The Android software then starts.

3. Populate a microSD card (case hybrid)[edit source]

In case of hybrid (eMMC / microSD card) configuration, you have to flash the data partitions (metadata and userdata) in a microSD card.

First you need to create the disk image:

 create-disk --hybrid

At this stage, the image st-android-optee-sd.raw has been created in the out subdirectory.

It's then possible to copy this image on a microSD card:

Linux (ex: Ubuntu) host

 dd if=st-android-optee-sd.raw of=<device_path> bs=8M conv=fdatasync status=progress
 sgdisk --move-second-header <microSD destination>

With:

<device_path>: the device identified in the system to access the microSD card (/dev/sdX for microSD card connected through USB dongle or /dev/mmcblkX for microSD card connected through reader, X is the instance associated to the Flash device).

Windows host

Example using HDD Raw Copy Tool :

Select the SOURCE: st-android-<boot_mode>-sd.raw
Select the TARGET: microSD card
Click on “START” button

4. Flash a dedicated image[edit source]

If an Android distribution is already installed and booted on the board, it's possible to update partitions one by one depending on the need. For example, if the kernel is rebuilt, just flash the boot (kernel), the dt (device tree) and the vendor images (modules).

First the device has to be restarted in fastboot mode:

Keep the reset button pressed until the board enters fastboot (USER1 for Evaluation board).

or

Run the command

 adb reboot bootloader

Finally, execute the flashing command:

 provision-device -i reboot

-i option means that a confirmation will be needed for flashing each partition at a time (select the partitions that need to be updated)
reboot option means that the device will reboot automatically at the end

5. Update an Android distribution[edit source]

If the content of the partitions dedicated to Android^TM needs to be updated (vendor,system, system_ext or product) after a rebuild, use ADB tool.

An overlayfs mechanism is used to allow updating files in read-only partitions, the first time you have to execute the following commands:

 adb root
 adb remount
 adb reboot

It is then possible to update the Android^TM partitions.

 adb root
 adb remount
 adb sync

Finally, the device needs to be rebooted to take these changes into account

 adb reboot