Setting up proper terminal size for serial connection to an embedded device

When you work over serial line on an embedded device usually the terminal size it set to 80x25.

There's an easy way, however, to setup your real terminal size, just add the following line to your profile script (~/.profile):

resize > /tmp/resize
. /tmp/resize

resize command detects real terminal size and sets COLUMNS and ROWS parameters accordingly:

# resize
COLUMNS=159;LINES=52;export COLUMNS LINES;

One just need to execute the output as sh commands (using source "." command).

Conflicting DHCP server locator under Linux

In order to locate conflicting DHCP server in your LAN execute the following command:

sudo dhcpdump -i eth4 | awk '/IP:/{SRC=$2 " " $3} /OP:.*BOOTPREPLY/{ print "DHCP server found:", SRC; }'

The restart your PC network (use DHCP to get new IP). If you see more than one IP address here:

DHCP server found: 192.168.4.1 (0:9:6b:a3:fc:4a)
DHCP server found: 192.168.1.1 (f8:d1:11:9e:1d:8b)
DHCP server found: 192.168.4.1 (0:9:6b:a3:fc:4a)
DHCP server found: 192.168.1.1 (f8:d1:11:9e:1d:8b)
DHCP server found: 192.168.4.1 (0:9:6b:a3:fc:4a)

Then you have two, conflicting DHCP servers in your network. You can use http://www.coffer.com/mac_find/ tool to locate the device type that causes the problems.

PlantUML - draw your diagrams declaratively

One picture is worth of thousand words. So true. Even if you describe some flow with many detailed paragraphs one sequence diagram might show the idea instantly to the reader much better than all the words.

Separation of diagram drawing software (Visio, Dia, ...) from your main documentation system (Google Docs, Latex, doxygen, ...) is not a good idea. Having no access to source of the diagram makes modification much harder to do (when original author is not available, you have, actually, re-draw the diagram from scratch to fix some minor change).

Text-based diagrams and some form of post-processing is the answer to above problem. You embed your documentation AND the diagrams in the document and tools change those into graphics when needed. Example of such systems cooperation is doxygen and plantuml.

Let's see how easy sequence diagram could be expressed in plantuml:

@startuml{sequence.png}
MainProcess -> Library: FacadeCall()
Library -> SSO: GetToken()
Library -> Server: CallService(token)
Server -> SSO: IsTokenValid(token)
@enduml

The result is rendered as diagram below:

There are more advanced functionality there, but I hope you have already caught the idea.

Next diagram type I'd like to explore is state diagram:

Meeting "minutes" in three simple steps

Nobody likes it. It's a boring duty you ought to do after a meeting. What? "Minutes", of course.

By "minutes" I mean: a note from the meeting (or a telco) that should be sent after a call to all participants involved in order to remind what has been agreed on the meeting and what action items are specified and who is responsible for implementation.



Is there a way to make this very useful tool more effective? The answer is: YES!

First of all: lets enumerate expected properties of those "minutes":

• easy to write
• do not skip/forget anything important
• allow to control if every action item has an assignee

Having above properties in mind I've implemented the following process using an online documents solution (Google Docs, to be specific):

• I send proposed agenda as online document link to every participants and I allow them to extend it if needed
• During the call I (or any participant) add action items and responsible persons to the document. Remember: concurrent editing is fun!
• A copy the document is sent after the call in the same e-mail thread as invitation
• And now: the previous step delivers your team "minutes"! Voila!

Everyone has R/W access to the document and this is the gag - you can delegate your job to add notes and complete document (including completeness checks) to meeting participants. They enjoy that as they're involved in the meeting flow and the output directly. Nobody is bored.

To speed things up you can add timestamp to each agenda item. Such meeting could never miss allocated time!

Implementation tracking is also easy - you can add ticket tracking ID (Jira, Redmine) to the minutes and assign appropriately.

Happy (not boring) meetings! :-)

Why EDID/HDCP information is important in monitoring solutions

EDID stands for "Extended Display Identification Data" and in IPTV solutions is used to provide detailed information on TV set capabilities and manufacturing information. HDCP ("High-bandwidth Digital Content Protection") is used for protecting high resolution content from being stolen by DVR. We typically count failed and successful HDCP connections.  This data is usually reported to central server using TR-69 protocol and/or proprietary protocols like Agama.

STB Development: TFTP+NFS boot methods - for dummies :-)

STB (Set Top Box) devices usually run from NAND partitions. All the rootfs is persisted in read-only filesystem (squashfs) and mounts additional R/W locations if needed (ramdisk for /tmp storage, at least). This setup works quite well for final deployment, but might be a bit problematic if you, actually, develop software stack and need to update and test many times per day.

This is the place where long-time forgotten network boot method comes to play.

In the old days (university) I remember "thin Solaris clients" that were used for programming classes. They had no hard disk and booted from network. What the boot process does look like?

Buildroot basics

If you are an embedded software developer like me chances are you use embedded Linux for the purpose. It's Open Source, has great tools support and is a great software environment where (almost) everything could be automated through command line interfaces.

Once you decide about operating system used the next step is to choose a build system that would be used for the task of building the software. There are few choices you can select from:

• use pre-built toolchain and rootfs and add your binaries and configuration files (i.e. STLinux for ST-based devices)
• use OpenEmbedded for full-featured buildsystem with packaging system included
• use BuildRoot for simple build system without packaging system included

Today I'm going to tell you about the 3rd option. Buildroot states their view on packaging systems for embedded development this way:

We believe that for most embedded Linux systems, binary packages are not necessary, and potentially harmful. When binary packages are used, it means that the system can be partially upgraded, which creates an enormous number of possible combinations of package versions that should be tested before doing the upgrade on the embedded device. On the other hand, by doing complete system upgrades by upgrading the entire root filesystem image at once, the image deployed to the embedded system is guaranteed to really be the one that has been tested and validated.

After few years with OpenEmbedded and few months with Buildroot I like the simplicity of Buildroot model. Below you can find basic (the most important in my opinion) concepts of Buildroot.

[SOLVED] VPN connectioin error: short read (-1): Message too long

If you encounter the following error during VPN connection:

pptp[12549]: nm-pptp-service-12543 warn[decaps_gre:pptp_gre.c:331]: short read (-1): Message too long

there's an easy fix. You have to lower your MTU (automatically obtained value was invalid).

First, you have to locate your VPN gateway address in syslog:

NetworkManager[11926]: <info> VPN Gateway: X.X.X.X

Then, you have to check minimum MTU toward this address:

$ traceroute --mtu X.X.X.X
traceroute to X.X.X.X (X.X.X.X), 30 hops max, 65000 byte packets
1  192.168.43.1 (192.168.43.1)  4.309 ms F=1380  4.042 ms  2.535 ms
2  * *^C

Then you have to change MTU it in your primary connection settings (network manager on Ubuntu below):



That's all!. No more spurious disconnects!