TS-4100 Debian Sections

Debian is a community run Linux distribution. Debian provides tens of thousands of precompiled applications and services. This distribution is known for stability and large community providing support and documentation. This distribution does not include the same support as Yocto for the GPU. OpenGL ES, Gstreamer, or OpenCL are not supported in Debian. The framebuffer is supported so 2D applications will still run well. Debian is also very well suited for headless applications.

Getting Started with Debian

Once installed the default user is "root" with no password.

• debian-armhf-jessie-latest.tar.bz2 (md5)

To prepare an SD card, use partitioning tools such as 'fdisk' 'cfdisk' or 'gparted' in linux to create a single linux partition on the SD card. See the guide here for more information. Once it is formatted, extract the above tarball with:

# Assuming your SD card is /dev/sdc with one partition
mkfs.ext3 /dev/sdc1
mkdir /mnt/sd/
sudo mount /dev/sdc1 /mnt/sd/
sudo tar xjf debian-armhf-jessie-latest.tar.bz2 -C /mnt/sd
sudo umount /mnt/sd
sync

Note:

The ext4 filesystem can be used instead of ext3, but it may require additional options. U-Boot does not support the 64bit addressing added as the default behavior in recent revisions of mkfs.ext4. If using e2fsprogs 1.43 or newer, the options "-O ^64bit,^metadata_csum" must be used with ext4 for proper compatibility. Older versions of e2fsprogs do not need these options passed nor are they needed for ext3.

To rewrite the eMMC the unit must be booted to SD or any other media that is not eMMC. Once booted, run the following commands.:

mkfs.ext3 /dev/mmcblk2p1
mkdir /mnt/emmc
mount /dev/mmcblk2p1 /mnt/emmc
wget -qO- https://files.embeddedTS.com/ts-socket-macrocontrollers/ts-4100-linux/distributions/debian/prev_releases/debian-armhf-jessie-latest.tar.xz | tar xj -C /mnt/emmc/
umount /mnt/emmc
sync

Note:

The ext4 filesystem can be used instead of ext3, but it may require additional options. U-Boot does not support the 64bit addressing added as the default behavior in recent revisions of mkfs.ext4. If using e2fsprogs 1.43 or newer, the options "-O ^64bit,^metadata_csum" must be used with ext4 for proper compatibility. Older versions of e2fsprogs do not need these options passed nor are they needed for ext3.

The same commands can be used to write a SATA drive by substituting /dev/mmcblk2p1 with /dev/sda1.

Debian Networking

From almost any Linux system you can use 'ip' command or the 'ifconfig' and 'route' commands to initially set up the network.

# Bring up the CPU network interface
ifconfig eth0 up

# Or if you're on a baseboard with a second ethernet port, you can use that as:
ifconfig eth1 up

# Set an ip address (assumes 255.255.255.0 subnet mask)
ifconfig eth0 192.168.0.50

# Set a specific subnet
ifconfig eth0 192.168.0.50 netmask 255.255.0.0

# Configure your route.  This is the server that provides your internet connection.
route add default gw 192.168.0.1

# Edit /etc/resolv.conf for your DNS server
echo "nameserver 192.168.0.1" > /etc/resolv.conf

Most networks will offer a DHCP server, an IP address can be obtained from a server with a single command in linux:

Configure DHCP in Debian:

# To setup the default CPU ethernet port
dhclient eth0
# Or if you're on a baseboard with a second ethernet port, you can use that as:
dhclient eth1
# You can configure all ethernet ports for a dhcp response with
dhclient

Systemd provides a networking configuration option to allow for automatic configuration on startup. Systemd-networkd has a number of different configuration files, some of the default examples and setup steps are outlined below.

/etc/systemd/network/eth.network

[Match]
Name=eth*

[Network]
DHCP=yes

To use DHCP to configure DNS via systemd, start and enable the network name resolver service, systemd-resolved:

systemctl start systemd-resolved.service 
systemctl enable systemd-resolved.service
ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf

For a static config create a network configuration for that specific interface.

/etc/systemd/network/eth0.network

[Match]
Name=eth0

[Network]
Address=192.168.0.50/24
Gateway=192.168.0.1
DNS=192.168.0.1

For more information on networking, see Debian and systemd's documentation:

• Systemd Networking Documentation
• Debian Documentation

Debian WIFI Client

If connecting to a WPA/WPA2 network, a wpa_supplicant config file must first be created:

wpa_passphrase yournetwork yournetworkpassphrase > /etc/wpa_supplicant/wpa_supplicant-wlan0.conf

Create the file /lib/systemd/system/wpa_supplicant@.service with these contents

[Unit]
Description=WPA supplicant daemon (interface-specific version)
Requires=sys-subsystem-net-devices-%i.device
After=sys-subsystem-net-devices-%i.device

[Service]
Type=simple
ExecStart=/sbin/wpa_supplicant -c/etc/wpa_supplicant/wpa_supplicant-%I.conf -i%I

[Install]
Alias=multi-user.target.wants/wpa_supplicant@%i.service

Create the file /etc/systemd/network/wlan0.network with:

[Match]
Name=wlan0

[Network]
DHCP=yes

See the systemctl-networkd example for setting a static IP for a network interface. The wlan0.network can be configured the same way as an eth.network.

To enable all of the changes that have been made, run the following commands:

systemctl enable wpa_supplicant@wlan0
systemctl start wpa_supplicant@wlan0
systemctl restart systemd-networkd

Debian WIFI Access Point

This section will discuss setting up the WiFi device as an access point that is bridged to an ethernet port. That is, clients can connect to the AP and will be connected to the ethernet network through this network bridge. The ethernet network must provide a DHCP server; this will be passed through the bridge to WiFi client devices as they connect.

It is also possible to run a DHCP client on the platform itself. In this case the hostapd.conf file needs to be set up without bridging and a DHCP server needs to be configured. Refer to Debian's documentation for more details on DHCP server configuration.

The 'hostapd' utility is used to manage the access point of the device. This is usually installed by default, but can be installed with:

apt-get update && apt-get install hostapd -y

Note:

The install process may start an unconfigured 'hostapd' process. This process must be killed before moving forward.

Modify the file "/etc/hostapd/hostapd.conf" to have the following lines:

ssid=YourWiFiName
wpa_passphrase=Somepassphrase
interface=wlan0
bridge=br0
auth_algs=3
channel=7
driver=nl80211
hw_mode=g
logger_stdout=-1
logger_stdout_level=2
max_num_sta=5
rsn_pairwise=CCMP
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP CCMP

Note:

Refer to the kernel's hostapd documentation for more wireless configuration options.

The access point can be started and tested by hand:

hostapd /etc/hostapd/hostapd.conf

Systemd auto-start with bridge to eth0

It is possible to configure the auto-start of 'hostapd' through systemd. The configuration outlined below will set up a bridge with "eth0", meaning the Wi-Fi connection is directly connected to the ethernet network. The ethernet network is required to have a DHCP server present and active on it to assign Wi-Fi clients an IP address. This setup will allow Wi-Fi clients access to the same network as the ethernet port, and the bridge interface will allow the platform itself to access the network.

Set up hostapd

First, create the file "/etc/systemd/system/hostapd_user.service" with the following contents:

[Unit]
Description=Hostapd IEEE 802.11 AP
Wants=network.target
Before=network.target
Before=network.service
After=sys-subsystem-net-devices-wlan0.device
After=sys-subsystem-net-devices-br0.device
BindsTo=sys-subsystem-net-devices-wlan0.device
BindsTo=sys-subsystem-net-devices-br0.device

[Service]
Type=forking
PIDFile=/run/hostapd.pid
ExecStart=/usr/sbin/hostapd /etc/hostapd/hostapd.conf -P /run/hostapd.pid -B

[Install]
WantedBy=multi-user.target

Then enable this in systemd:

systemctl enable hostapd_user.service
systemctl enable systemd-networkd

Set up bridging

Create the following files with the listed contents.

"/etc/systemd/network/br0.netdev"

[NetDev]
Name=br0
Kind=bridge

"/etc/systemd/network/br0.network"

[Match]
Name=br0

[Network]
DHCP=yes

"/etc/systemd/network/bridge.network"

[Match]
Name=eth0

[Network]
Bridge=br0

Debian Application Development

Debian Jessie Cross Compiling

Debian Jessie previously provided cross compilers via the Emdebian project. However, Emdebian has been unmaintained for a number of years and is no longer able to provide a viable install package. In order to cross compile from a Debian Jessie workstation, a third party cross compiler is required.

A Debian Jessie install on a workstation has the ability to build for the same release on other architectures using Debian binary libraries. A PC, virtual machine, or chroot will need to be used for this. Install Debian Jessie for your workstation here.

From a Debian workstation (not the target), run the following commands to set up the cross compiler. Note that this expects a 64-bit Debian Jessie install on the workstation. 32-bit installations are not supported at this time.

# Run "lsb_release -a" and verify Debian 8.X is returned.  These instructions are not
# expected to work on any other version or distribution.

cd ~
wget http://ftp.embeddedTS.com/ftp/ts-arm-sbc/ts-7553-V2-linux/cross-toolchains/gcc-linaro-4.9-2016.02-x86_64_arm-linux-gnueabihf.tar.xz
# The above toolchain is from Linaro. Other cross compilers can be used but have not been tested.
mkdir cross_compiler
tar xvf gcc-linaro-4.9-2016.02-x86_64_arm-linux-gnueabihf.tar.xz -C ~/cross_compiler
export PATH=$PATH:~/cross_compiler/gcc-linaro-4.9-2016.02-x86_64_arm-linux-gnueabihf/bin/
# The 'export' command needs to be run every time the user logs in. It is possible to add this command to the user's ".bashrc" file
# in their home directory to ensure it is automatically run every time the user is logged in.
su root
dpkg --add-architecture armhf
apt-get update
apt-get install build-essential

This will install a toolchain that can be used with the prefix "arm-linux-gnueabihf-". The standard GCC tools will start with that name, eg "arm-linux-gnueabihf-gcc".

The toolchain can now compile a simple hello world application. Create hello-world.c on the Debian workstation:

#include <stdio.h>
int main(){
    printf("Hello World\n");
}

To compile this:

arm-linux-gnueabihf-gcc hello-world.c -o hello-world
file hello-world

This will return that the binary created is for ARM. Copy this to the target platform to run it there.

Debian Jessie supports multiarch which can install packages designed for other architectures. On workstations this is how 32-bit and 64-bit support is provided. This can also be used to install armhf packages on an x86 based workstation.

This cross compile environment can link to a shared library from the Debian root. The package would be installed in Debian on the workstation to provide headers and ".so" files. This is included in most "-dev" packages. When run on the arm target it will also need a copy of the library installed, but it does not need the -dev package. Note that since the cross compiler used is 3rd party and not directly from Debian, some compile commands that include libraries will need additional arguments to tell the compiler and linker where on the workstation to find the necessary headers and libraries. Usually, the additional arguments will look like the following string, however adjustments may need to be made depending on the application.

 -I/usr/include -L/usr/lib/arm-linux-gnueabihf -L/lib/arm-linux-gnueabihf -Wl,-rpath=/usr/lib/arm-linux-gnueabihf,-rpath=/lib/arm-linux-gnueabihf

apt-get install libcurl4-openssl-dev:armhf

# Download the simple.c example from curl:
wget https://raw.githubusercontent.com/bagder/curl/master/docs/examples/simple.c
# After installing the supporting library, curl will link as compiling on the unit.
arm-linux-gnueabihf-gcc -I/usr/include -L/usr/lib/arm-linux-gnueabihf -L/lib/arm-linux-gnueabihf -Wl,-rpath=/usr/lib/arm-linux-gnueabihf,-rpath=/lib/arm-linux-gnueabihf simple.c -o simple -lcurl

Copy the binary to the target platform and run on the target. This can be accomplished with network protocols like NFS, SCP, FTP, etc.

If any created binaries do not rely on hardware support like GPIO or CAN, they can be run using qemu.

# using the hello world example from before:
./hello-world
# Returns Exec format error
apt-get install qemu-user-static
./hello-world

Debian Installing New Software

Debian provides the apt-get system which allows management of pre-built applications. The apt tools require a network connection to the internet in order to automatically download and install new software. The update command will download a list of the current versions of pre-built packages.

Older Debian releases are moved to a different server to indicate it is no longer getting security updates. To download packages for these older distributions, edit /etc/apt/sources.list to only have the following lines:

Jessie:

deb http://archive.debian.org/debian/ jessie main
deb-src http://archive.debian.org/debian/ jessie main

Wheezy:

deb http://archive.debian.org/debian/ wheezy main
deb-src http://archive.debian.org/debian/ wheezy main

After modifying that file, be sure to update the package list:

apt-get update

A common example is installing Java runtime support for a system. Find the package name first with search, and then install it.

root@ts:~# apt-cache search openjdk
jvm-7-avian-jre - lightweight virtual machine using the OpenJDK class library
freemind - Java Program for creating and viewing Mindmaps
icedtea-7-plugin - web browser plugin based on OpenJDK and IcedTea to execute Java applets
default-jdk - Standard Java or Java compatible Development Kit
default-jdk-doc - Standard Java or Java compatible Development Kit (documentation)
default-jre - Standard Java or Java compatible Runtime
default-jre-headless - Standard Java or Java compatible Runtime (headless)
jtreg - Regression Test Harness for the OpenJDK platform
libreoffice - office productivity suite (metapackage)
icedtea-7-jre-jamvm - Alternative JVM for OpenJDK, using JamVM
openjdk-7-dbg - Java runtime based on OpenJDK (debugging symbols)
openjdk-7-demo - Java runtime based on OpenJDK (demos and examples)
openjdk-7-doc - OpenJDK Development Kit (JDK) documentation
openjdk-7-jdk - OpenJDK Development Kit (JDK)
openjdk-7-jre - OpenJDK Java runtime, using Hotspot Zero
openjdk-7-jre-headless - OpenJDK Java runtime, using Hotspot Zero (headless)
openjdk-7-jre-lib - OpenJDK Java runtime (architecture independent libraries)
openjdk-7-source - OpenJDK Development Kit (JDK) source files
uwsgi-app-integration-plugins - plugins for integration of uWSGI and application
uwsgi-plugin-jvm-openjdk-7 - Java plugin for uWSGI (OpenJDK 7)
uwsgi-plugin-jwsgi-openjdk-7 - JWSGI plugin for uWSGI (OpenJDK 7)
                                                       

In this case you will want the openjdk-7-jre package. Names of packages are on Debian's wiki or the packages site.

With the package name apt-get install can be used to install the prebuilt packages.

apt-get install openjdk-7-jre
# More than one package can be installed at a time.
apt-get install openjdk-7-jre nano vim mplayer

For more information on using apt-get refer to Debian's documentation here.

Debian Setting up SSH

To install ssh, install the package as normal with apt-get:

apt-get install openssh-server

Make sure the device is configured on the network and set a password for the remote user. SSH will not allow remote connections without a password or a valid SSH key pair.

passwd root

Note:

The default OpenSSH server will not permit root to login via SSH as a security precaution. To allow root to log in via ssh anyway, edit the /etc/ssh/sshd_config file and add the line PermitRootLogin yes in the authentication section. This change will take effect after reboot or after sshd service restart.

After this setup it is now possible to connect from a remote PC supporting SSH. On Linux/OS X this is the "ssh" command, or from Windows using a client such as PuTTY.

Note:

If a DNS server is not present on the target network, it is possible to save time at login by adding "UseDNS no" in /etc/ssh/sshd_config.

Debian Starting Automatically

A systemd service can be created to start up headless applications. Create a file in /etc/systemd/system/yourapp.service

[Unit]
Description=Run an application on startup

[Service]
Type=simple
ExecStart=/usr/local/bin/your_app_or_script

[Install]
WantedBy=multi-user.target

If networking is a dependency add "After=network.target" in the Unit section. Once you have this file in place add it to startup with:

# Start the app on startup, but will not start it now
systemctl enable yourapp.service

# Start the app now, but doesn't change auto startup
systemctl start yourapp.service

Note:

See the systemd documentation for in depth documentation on services.

To start an application on bootup with X11 instead change the x-session-manager. By default the system starts xfce:

root@ts:~# ls -lah /usr/bin/x-session-manager 
lrwxrwxrwx 1 root root 35 May 26  2015 /usr/bin/x-session-manager -> /etc/alternatives/x-session-manager
root@ts:~# ls -lah /etc/alternatives/x-session-manager
lrwxrwxrwx 1 root root 19 May 26  2015 /etc/alternatives/x-session-manager -> /usr/bin/startxfce4

The x-session can be modified to only start specified processes. Create the file /usr/bin/mini-x-session with these contents:

#!/bin/bash
matchbox-window-manager -use_titlebar no &

exec xfce4-terminal

You may need to "apt-get install matchbox-window-manager." first. This is a tiny window manager which also has a few flags that simplify embedded use. Now enable this session manager and restart slim to restart x11 and show it now.

chmod a+x /usr/bin/mini-x-session
rm /etc/alternatives/x-session-manager
ln -s /usr/bin/mini-x-session /etc/alternatives/x-session-manager
service slim restart

If the x-session-manager process ever closes x11 will restart. The exec command allows a new process to take over the existing PID. In the above example xfce4-terminal takes over the PID of x-session-manager. If the terminal is closed with commands like exit the slim/x11 processes will restart.