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In this chapter, common configuration and maintenance tasks are described.

Initial Device Configuration

Starting from the Dunfell release of Linux Yocto, SECO Northern Europe devices no longer support dynamic change of device configuration (e.g. display or touch settings) via xml file with the xconfig script. Initial device configurations need to be made before OS installation and will be attached permanently to that installation. Further changes down the line require a new installation of the OS.

This has the benefit of a simplified device boot, as well as an accelerated boot speed. While later configuration changes might be more complicated, with the nature of embedded systems, changes are not very common and an improved boot process would be better for the system overall.

The process of booting into the Flash-N-Go System is described in the chapter [Deploying the Linux system to the target]. Within Flash-N-Go System, the xconfig script can be called to modify the device configuration.

 Working with xconfig

Calling xconfig to show available option:

FLASH-N-GO:/# xconfig

List the installed configuration of the device:

FLASH-N-GO:/# xconfig list

Delete the existing display config:

FLASH-N-GO:/# xconfig delnode -y -p /variables/display

Import an xml configuration file, in this example a display config located in /mnt/mstick1/:

FLASH-N-GO:/# xconfig import /mnt/mstick1/<my-display-config>.xml -y

More detail about Flash-N-Go infrastructure can be found here.

SECO Northern Europe system configuration

As with xconfig, sconfig also no longer support dynamic changes of configuration in the target OS. A new OS installation is required for the new setting to take effect.

Some parts of the system configuration are stored in an xml file stored on one of the boot partitions of the eMMC. This information is shared between the backup OS Flash-N-Go System and the main OS, but also persistent between normal OS installations.

The shared information is stored in an xml file called config.xml, found in /etc/shared. For this purpose, there is a link to the script at /usr/sbin/sconfig which can be called without the absolute path:

root@santaro:~# sconfig

   dhcp        true
   ip          192.168.1.1
   mask        255.255.255.0
   gateway     192.168.1.100
   mac         0x00:0x07:0x8E:0x35:0xA4:0x8A
   name        GFMM03515530
   serial      03515530

Call without parameter to show the list of current configurations on the system. Call with -h to show additional help.

If the script is called with a setting as parameter, the setting is read from the XML configuration and displayed on the console. 

root@santaro:~# sconfig gateway
192.168.1.1

If additionally a value is appended, this value is updated to the according setting in the XML configuration.

root@santaro:~# sconfig gateway 192.168.1.10
root@santaro:~# sconfig gateway
192.168.1.10

The ’name’ set with sconfig is also used as hostname for the device. It defaults to GFMM<serial number>.

Network configuration

The Network Manager service is responsible for initializing all network interfaces at system startup and when an ethernet cable or a WLAN stick is plugged in.
The Network Manager stores its config files in the /etc/NetworkManager directory. Normally there is no need to change those files directly as there are some tools available to configure the network.

More information about Network Manager can be found here.

WLAN

While SANTOKA has a built-in WLAN module, all other SECO Northern Europe products support WLAN using WLAN USB dongles. A list of supported devices can be found in the BSP release notes. WLAN can be used as client or provide an own network as Access Point.

Network management is done through nmcli, which is a command-line client for the Network Manager and reporting network status. A detail explanation of nmcli usage can be found here and here.

 Enable WLAN device

View status of all network devices:

nmcli dev status

Check status of WLAN device:

nmcli radio wifi

If disabled, enable with the command:

nmcli radio wifi on

Configure as WLAN client

 Connect to a network

Scan for nearby networks:

nmcli dev wifi list

Note the name of networks listed under the column SSID, to connect a desired network:

nmcli dev wifi connect <network-name> password <network-password>

Once successfully connected, test the connection with ping:

ping north.seco.com

Network Manager will save the connection and auto-connect on reboot, so you don't have to worry about issuing the command every time the device is booted.

 Managing connections

View all of the saved connection:

nmcli con show

Disconnect from an active connection:

nmcli con down <network-name>

Connect to another saved connection:

nmcli con up <network-name>

Delete a network from the list:

nmcli con delete <network-name>

Configure as WLAN Access Point

It is possible to configure the device to act as WLAN Access Point though this feature is not supported by all WLAN modules and WLAN drivers.

 WLAN access point with sub net

To setup a WLAN Access point with own sub network including a DHCP service using the Network Manager use following commands:

nmcli connection down wlan0-sconfig-autogenerated
nmcli con add type wifi ifname wlan0 con-name Hotspot autoconnect no ssid test
nmcli con modify Hotspot 802-11-wireless.mode ap 802-11-wireless.band bg ipv4.method shared wifi-sec.key-mgmt wpa-psk wifi-sec.psk "secret_passphrase"
nmcli con up Hotspot

This creates a “test” network with the password “secret_passphrase”. The connection to identify this setup in the Network Manager is called Hotspot. This kind of WLAN access point assigns each client an own IP Address in its own sub net, starting with 10.42.0.1 by default. Accesses to the internet over an ethernet connection are using NAT (network address translation). This way the clients are not visible from the ethernet.

To remove this connection use:

nmcli con delete Hotspot

Compliance to Regulatory Domain

The WLAN modules perform wireless communication that is subject to different local regulations, depending on where the module is used. For example, in the USA the FCC does not allow communication to be performed on channels 12, 13, and 14, whereas in Japan communication is allowed on all channels 1 to 14.

CRDA Regulatory Domain Setting

Most of our systems allow the configuration of the regulatory domain via the standard CRDA support of the Linux kernel.

 View and change setting for LM808 and internal modules

Show current settings:

iw reg get

Set domain to Germany:

iw reg set DE

Set domain to USA:

iw reg set US

Show enabled channels and other information:

iw list

Show enabled channels:

iwlist wlan0 channel

These settings use a general strategy of regdomain compliance:

  • The system uses a default "world" regdomain.

  • The wifi adapter can define its own regdomain. (E.g., the PCEAN2i Module is configured to US.)

  • A user can set a regdomain.

In any case only the common subset of the three possible settings is enabled, so the permissions can usually
only shrink to be more compliant.

The world regdomain is a bit special. It receives configurations on channels that are not allowed everywhere in the world, which are enabled only if a router announces its network on such a channel.

Run an application at startup

The init system changed from System V to systemd. This means that all scripts in /etc/init.d are gone and replaced by systemd units. systemd uses so-called unit-files to configure services to start and stop. The tool systemctl is the main userspace tool to control these if needed.

 Configuring application startup

View list of installed services

root@santaro:~# systemctl list-unit-files

Disable/enable a service from automatic startup

root@santaro:~# systemctl disable <service-name>
root@santaro:~# systemctl enable <service-name>

Check the status of a service

root@santaro:~# systemctl status <service-name>

Example: disable the demo from startup

root@santaro:~# systemctl disable guf-show-demo

Watchdog

Generally a watchdog is a subsystem that monitors the system state in some way and executes a reset when a malfunction is detected. The watchdog service is built of a hardware watchdog device and a linux service.

The hardware watchdog device on SECO Northern Europe devices is capable to execute a hardware reset when not triggered in time. The device node for the hardware watchdog is /dev/watchdog.

The watchdog service is able to monitor different system parameters, like the system load, and can take different actions if any system parameter is out of a defined range. Those repair actions can be simple cleanup scripts or the execution of a reboot or shutdown.

The service opens the hardware watchdog and triggers it regularly. When the service crashes or the execution of a repair script fails, the hardware watchdog isn’t triggered in time and a hardware reset will be executed.

The default state of the service is disabled.

 Configure watchdog

The file /etc/systemd/system.conf contains option to configure the watchdog logic.

RuntimeWatchdogSec=0

Default value of 0 means watchdog is disabled, set to a value (e.g. 20s) to reboot the system after there is no keep-alive ping during the given interval.

RebootWatchdogSec=10min
ShutdownWatchdogSec=10min
KExecWatchdogSec=0

Further configuration to watchdog timing at reboot, shutdown, and by kexec, respectively.

 Add watchdog logic to running service

To add the watchdog logic to a running service, simply add WatchdogSec=<interval> to the systemd unit file of that service.

[Unit]
Description=My unit

[Service]
ExecStart=/usr/bin/myunit
WatchdogSec=30s

Further documentation and additional configuration can be found here and here.

Power down mode

The system can enter a power down mode to reduce power consumption when the system is not in use. In this mode all PLLs are disabled, CPU voltages are lowered and several hardware components are powered down. The overall power consumption should be less than 500 mW in this mode but actually depends on the device and its hardware assembly option.

 Enter power down mode

Power down mode is entered using the following command:

root@santaro:~# echo mem > /sys/power/state

The average time it takes to enter power down mode has been measured at 364+-5ms (last byte on UART RX until voltage drop on VDDSOC).

There are different possibilities to make the system wake up from the power down mode. Wakeup sources have to be configured before entering power down mode, otherwise the system cannot be woken up.

 Wakeup sources

RTC: The CPU internal RTC can be configured to wake up the system after a specified time. The following command wakes the system up at 20 seconds after the command has been executed:

root@santaro:~# echo +20 > /sys/class/rtc/rtc1/wakealarm

RS232/RS485/MDB: All serial interfaces can be configured to wake up the system on incoming bytes. The following command wakes the system up as soon as a byte is received on the serial debug port:

root@santaro:~# echo enabled > /sys/class/tty/ttymxc0/power/wakeup

The average time it takes to wake up from power down mode using the serial debug port has been measured 1326+-4ms (first byte on UART RX until last byte on UART TX).

The first few incoming bytes after and including the wakeup byte might be truncated and not received by the UART driver.

Reboot, Halt and Poweroff

As you probably have noticed already, none of our SECO Northern Europe devices are equipped with any kind of power button. This means, they will start booting and running an OS as soon as an external power-supply is connected and turned-on and the only way to turn the device off is to disconnect the external power-supply.

The devices are not designed to be turned-off under software-control.

The common Unix/Linux utilities to shutdown the system behave accordingly:

  • reboot: will stop all login-services, stop all running applications, flush all caches, unmount all filesystems and safely reboot the system.

  • halt: will stop all login-services, stop all running applications, flush all caches, unmount all filesystems and just "halt" the system, so that a user may safely disconnect the power-supply without risking any data-loss.

  • poweroff: according to Unix/Linux conventions for systems that cannot turn-off themselves, will do just the same as halt.

This means, as per Linux/Unix convention for systems that can’t turn-off themselves, none of these commands will turn-off device power; not even the display power. The halt and poweroff commands will only ensure that the system is put in a state, where no user-processes are running anymore and all data has been written back to storage media.

Kernel command line

The kernel command line can be used to change some kernel features.

Be careful changing the command line, as it can easily break the booting process of your device. If booting fails after those changes, you will need to boot into Flash-N-Go System and correct the settings. In this case, please refer to the Flash-N-Go infrastructure manual.

 Open and edit the command line

To change the kernel command line, the boot partition needs to be mounted:

mount /dev/mmcblk0p2 /mnt

Open the boot configurator file to edit:

nano /mnt/boot.cfg

The boot configuration normally looks similar to this:

# Only load linux image as it also contains the configured devicetree attached
load linuximage
exec "console=ttymxc0,115200 root=/dev/mmcblk0p3 rootflags=data=journal rootwait rootfstype=ext4 cma=128M loglevel=6 vt.global_cursor_default=0 vt.color=0xF7 fbcon=logo-pos:center,logo-count:1,rotate:0"

The last line is the kernel command line. Options can be added to the end.

Integrating customized driver (module loading)

SECO Northern Europe devices can automatically load customized drivers (module) on boot with the help of systemd. The systemd-modules-load.service is responsible for external module loading on system startup. Users can customize this service to integrate their own driver to the system.

 Load a customized driver

First check if systemd-modules-load.service is activated:

root@santaro:~# systemctl status systemd-modules-load.service

Create the config file in /etc/modules-load.d/:

root@santaro:~# cd /etc/modules-load.d/
root@santaro:/etc/modules-load.d/# touch <module-name>.conf

Edit the file to only contain the module name:

<module-name>

Next time the system reboots, the module will be automatically loaded.

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