XELK-TN-001: Using Chromium browser as an Embedded GUI

Info Box Applies to Axel Ultra Applies to AXEL ESATTA Applies to Axel Lite Applies to SBC AXEL

This application note has been validated starting from the XELK 4.0.0 kit version.

History

Version	Date	XELK version	Notes
1.0.0	Oct 2019	4.0.0

Introduction

Starting from XELK 4.0.0 a new root file system image can be created using Yocto recipes provided by DAVE's XELK BSP.

The new axel-image-x11-browser Yocto image includes the recipes for adding the following packages:

• Chromium browser
• apache2 web server
• PHP with apache2 plugin

Architecture

The new root file system can be a complete solution for creating GUI (Graphical User Interface) using popular knowledge as per designing HTML web pages. The apache2 web server is configured for starting at boot time: the web pages, stored on local file system, will be directly shown on the Chromium browser which is configured for looking on localhost interface.

Here below a command line example for chromium using this configuration:

google-chrome --test-type --kiosk -disable-gpu --start-maximized http://localhost:80/phpinfo.php

How to configure

Web server

Apache2 is used as a web server let the embedded system to provide the HTML pages used for creating the GUI. Once installed into the rfs, apache2 will be automatically started using the following configuration file:

/etc/apache2/httpd.conf

It is possible to see that apache2 uses the web page present into the /usr/share/apache2/htdocs directory:

root@imx6qxelk:~# cat /etc/apache2/httpd.conf | grep htdocs
DocumentRoot "/usr/share/apache2/htdocs"
<Directory "/usr/share/apache2/htdocs">
root@imx6qxelk:~#

PHP

For demonstration purposes the PHP info page is loaded as the home page for our web server running on the system:

root@imx6qxelk:~# cat /usr/share/apache2/htdocs/.htaccess
DirectoryIndex phpinfo.php
root@imx6qxelk:~# cat /usr/share/apache2/htdocs/phpinfo.php
<?php

phpinfo();

?>
root@imx6qxelk:~#

In this way, the PHP info page is shown when the web browser is started on localhost.

Graphical backend

Chromium browser has been built on top of X11 backend: the Yocto build automatically starts the X11 Desktop which should be avoided for having a clean boot with only the browser displayed.

For this pruposes, the desktop will be displayed and the X11 server will be started only as backend:

root@imx6qxelk:~# systemctl disable xserver-nodm.service
Removed /etc/systemd/system/multi-user.target.wants/xserver-nodm.service.
root@imx6qxelk:~# 

Then, the new X service will be created and started

root@imx6qxelk:~# cat /etc/systemd/system/X.service
[Unit]
Description=X
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=1
User=root
ExecStart=/usr/bin/X -nocursor

[Install]
WantedBy=multi-user.target

root@imx6qxelk:~# systemctl enable X
Created symlink /etc/systemd/system/multi-user.target.wants/X.service → /etc/systemd/system/X.service.
root@imx6qxelk:~#

Chromium

In the same way of the web server, chormiumcam be started using a proper service:

root@imx6qxelk:~# cat /etc/systemd/system/browser.service
[Unit]
Description=ChromiumBrowser
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=1
User=root
ExecStart=/home/root/browser.sh

[Install]
WantedBy=multi-user.target

and a script which will be started at boot time:

root@imx6qxelk:~# cat browser.sh
#!/bin/bash

export DISPLAY=:0

google-chrome --test-type --kiosk -disable-gpu --start-maximized http://localhost:80/phpinfo.php
root@imx6qxelk:~#

As per the command line parameters, chromium is started with the following properties:

• Full screen mode: --start-maximized
• Kiosk mode: --kiosk
• removing warning popus: --test-type

For a touch screen interaction, it is possible to install a Virtual Keyboard available on the chrome Google store. This is very easy starting chrome on the proper URL and then installing it:

root@imx6qxelk:~# google-chrome https://chrome.google.com/webstore/detail/virtual-keyboard/pflmllfnnabikmfkkaddkoolinlfninn