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Author: hfreyther

Using setitimer of your favorite posix kernel

Using setitimer of your favorite posix kernel

As this was requested in a comment of a previous post and knowing your kernel helps to write better performing systems here is a small information of how to use the interval timers provided by your posix kernel. What is the interval itime?r The interval timer is managed and provided by your kernel. Everytime the interval of the timer expires the kernel wil send a signal to your application. The kernel is providing three different interval timers for every application….

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Things I didn’t know about RTP and AMR

Things I didn’t know about RTP and AMR

Oh my god… Looking at an AMR payload wrapped in RTP, wrapped in UDP, wrapped in IP… one will recognize that there is a +70% overhead on payload vs. header… The other thing is… the AMR payload can have a CRC or not but it is not indicated in the RTP header and must be signalized out of band… it took someone a while to figure it out. Hurray on having clever colleagues.

Dealing with Performance Improvements

Dealing with Performance Improvements

I hope this post is educational and help the ones among us doing performance optimisations without any kind of measurement. If you do these things without a benchmark you are either a genuis or very likely your application is going to run slower. I’m not going to talk about performance analysis right now but tools like OProfile, callgrind, sysprof and speedprof are very handy utilities. The reason I’m writing this up is that I saw a performance regression in one…

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Explorations in the field of GSM

Explorations in the field of GSM

Something like 14 months ago I had no idea about GSM protocols, 12 months ago I was implementing paging for OpenBSC, beginning from last summer I explored SS7 and SCCP, wrote a simple SCCP stack for On-Waves. Started to implement the GSM A Interface for OpenBSC, the last week I saw myself learning more about MTP Level3. With the Osmocom I start to explore GSM Layer 1 (TDMA, bursts, syncing), GSM Layer 2 (LAPDm) and on GSM Layer3 we mostly…

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Conclusions of my QtWebKit performance work

Conclusions of my QtWebKit performance work

My work on QtWebKit performance came to a surprising end late last month. It might be interesting for others how QtWebKit compares to the various other WebKit ports, where we have some strong points and where we have some homework left todo and where to pickup from where I had to leave it. Memory consumption Before I started our ImageDecoderQt was decoding every image as soon as the data was complete. The biggest problem with that is that the ImageSource…

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On getting Free Support

On getting Free Support

Most of the things I know about Software and Hardware I have from reading books, looking at sourcecode but most importantly people willing to answer my questions on IRC and giving me a direction I could look for answers. Now it seems to be my part to give back and help others to gain knowledge, but some things have changed. Free Software has made it to the mainstream, so besides hackers that want to understand things, we do have paid…

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Reverse engineering with okteta

Reverse engineering with okteta

In the last week I was hacking on OpenBSC to make GSM 12.21 Software Load usable for the ip.access nanoBTS. The difficulta was not within GSM 12.21 as Harald had it implemented for the Siemens BS11 BTS. The difficulty was that some messages need to contain paramaters and these come directly from the firmware file which ultimately means that one needs to understand the firmware file format to extract these. okteta came to rescue me and it was extremely good…

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Looking back to 2009

Looking back to 2009

The second year as part time freelancer has passed. Looking back the most significant things are: Signing the contribution agreement for gdb and glibc with the Free Software Foundation and trying to contribute to both projects. So picking future work will always have to be compatible with this. Hacked on OpenBSC. At first just simple stuff like a telnet interface, paging and later doing paid work for On Waves to add SCCP over IP, GSM 08.08 and other things for…

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Kafka’s Briefe an den Vater

Kafka’s Briefe an den Vater

I used to read books of Franz Kafka a lot, I loved his struggle with his father as I could relate to it. I loved the idea if writing letters in form of liberating myself. But in recent years as I got older and parents became less important. So the last thing I will ever say about my “father” (and in case he reads it, as even old people can use computers…). I have no memory left of you, I…

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(Qt)WebKit Sprint in Wiesbaden

(Qt)WebKit Sprint in Wiesbaden

The sprint is over for some time. You can see summaries of the different sessions and some slides in the wiki. Besides talking about QtWebKit and how to improve it (API, features, speed, make people aware that they can contribute, influence the release schedule, policies.. *hint*) the thing that has impressed me the most is unrelated to coding. We all hear when someone from our Community is leaving the Qt department, and we always wonder how life will continue, who…

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