Embedded Networking

Nowadays everything and anything are connected using Internet Protocols: TCP, UDP, RTP, ARP, IGMP... the list goes on and on. However, embedded systems are frequently island systems, that are not connected to the usual support services such as DHCP and DNS. IP addresses are static and there are no gateways to other nets.

Island Networks

When you plug an office laptop computer into a typical embedded net, nothing happens, your machine remains unconfigured and you cannot access anything. Testing and debugging a modern system therefore requires a little bit of advanced networking knowledge.

In order to communicate on a net, your machine needs at least two things to be configured: IP Address and Subnet Mask, but before you can set it, you first have to disable the NetworkManager auto-configuration utility, since in an embedded system, it is more of a hindrance than a help.

Each time you unplug a cable or power down the device your laptop computer is connected to, Network Manager tends to forget the IP settings and when you replug it, you got to set everything up all over again. This gets annoying super quick.

Network Manager

To save your sanity, disable NetworkManager with one of these commands:
# service NetworkManager stop

or
# systemctl stop NetworkManager.service
# systemctl disable NetworkManager.service

or
# killall NetworkManager

Network Settings

Once NetworkManager is truly dead, see what the available network devices are:

# ifconfig

# ip link show

Now you can set a static address and be assured that it will stick:

# ifconfig em1 192.168.111.1 netmask 255.255.255.0 up

# ip addr add 192.168.111.1/24 dev em1

# ip link set em1 up

There Is More Than One Way To Do It (TIMTOWDI).

Going back to Normal

When you need to check you email or do a search for information and you need to plug the machine back into a wall socket, you got to restart the network, or just restart Network Manager.

# systemctl restart network.service

# systemctl restart NetworkManager.service

Happy debugging!

Comments

Unlock CRA PDF Forms

Unlock Canada Revenue Agency PDF Forms It appears that there is a relatively new PDF feature to prevent casual copying and saving of a file and that some programs save PDF files with these foolish features active by default. Many forms from the Canada Revenue Agency are locked in this way, which makes it difficult to do one's taxes, since one can fill the form, but cannot save it. One can only print the form. It should be possible to print to a file or export it to a new PDF file, but it is far better to reset the annoying anti-taxpayer flags, since the 'printed' form cannot be edited easily any more and I always manage to make a mistake or three that need to be corrected after review. If there is a Linux (virtual) machine handy, install qpdf and use it to reset the silly flags: $ su - password # dnf update # dnf install qpdf # exit $ qpdf --decrypt lockedfile.pdf unlockedfile.pdf One doesn't need a password to unlock these flags, so the fix is instant. La voila! He...

Parasitic Quadrifilar Helical Antenna

This article was reprinted in OSCAR News, March 2018: http://www.amsat-uk.org If you want to receive Satellite Weather Pictures , then you need a decent antenna, otherwise you will receive more noise than picture. For polar orbit satellites, one needs an antenna with a mushroom shaped radiation pattern . It needs to have strong gain towards the horizon where the satellites are distant, less gain upwards where they are close and as little as possible downwards, which would be wasted and a source of noise. Most satellites are spin stabilized and therefore the antenna also needs circular polarization, otherwise the received signal will flutter as the antennas rotate through nulls. The helical antenna, first proposed by Kraus in 1948, is the natural solution to circular polarized satellite communications. It is a simple twisted wire - there seems to be nothing to it. Various papers have been published on helix antennas, so the operation is pretty well ...

Weather Satellite Turnstile Antennas for the 2 meter Band

NEC2, 2 m band, 146 MHz, Yagi Turnstile Simulation and Build This article describes a Turnstile Antenna for the 2 meter band, 146 MHz amateur satcom, 137 MHz NOAA and Russian Meteor weather satellites. Weather satellite reception is described here . A quadrifilar helical antenna is described here . Engineering, is the art of making what you need, from what you can get. Radiation Pattern of the Three Element Yagi-Uda Antenna Once one combine and cross two Yagis, the pattern becomes distinctly twisted. The right hand polarization actually becomes visible in the radiation pattern plot, which I found really cool. Radiation Pattern of Six Element Turnstile Antenna Only a true RF Geek can appreciate the twisted invisible inner beauty of a herring bone antenna... Six Element Turnstile Antenna Essentially, it is three crosses on a stick. The driven elements are broken in the middle at the drive points. The other el...

Aeronetworks sro - Airborne Linux

Search This Blog