Category Archives: Development

Development, Open Source

Video: How to build Rockbox

I recorded a 10 minute screencast on how to build Rockbox from SVN (on Linux) just now. It’s something I’ve been meaning to do for a long time since I believe a lot of users need to get this shown rather than just a static text describing it. It really is easy and I think my video shows that.

rockboxbuild

The video is available as:

This recording was done using recordmydesktop. I did resize down my browser and reduce the font size to make it look decent in the smaller window. I consider this shot a bit of a test on how it works, and what I can do with it.

Development, Electronics

USB converter woes

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USB to rs232 converters are just never sold properly advertising what chip’s inside and right now I want to know if this one UART I’m working with perhaps is not playing fine with my existing converter cable.

I have this XScale PXA270 on a toradex-colibriboard, and it has only one full featured RS232 (FFUART) and I’m about to move things over to the lesser featured BTUART.

A theory is that my current USB converter that is based on a “Prolific PL2303” doesn’t play nicely on the serial port that isn’t a full RS232.

So I ran off and bought a new cable. I grabbed the only model I found in my local Kjell & Company store – it’s quite different looking than my existing but there’s no hint anywhere on the package or inside of it that says what chipset that empowers it.

A quick drive back home (I’m working from home in this assignment), I plugged it in and I got to see this depressingly familiar dmesg output:

usbcore: registered new interface driver usbserial
usbserial: USB Serial support registered for generic
usbcore: registered new interface driver usbserial_generic
usbserial: USB Serial Driver core
usbserial: USB Serial support registered for pl2303
pl2303 2-2.4:1.0: pl2303 converter detected
usb 2-2.4: pl2303 converter now attached to ttyUSB0
usbcore: registered new interface driver pl2303
pl2303: Prolific PL2303 USB to serial adaptor driver

So what now? I hate how (my) computers these days don’t have serial ports while the entire embedded world still very much uses them. I think I’ll go searching in my closet to see if I can find an old crap computer with a serial port to try.

Another theory is that the port simply is broken hw-wise on the dev board but that’s harder to check for me right now.

Update: it was (as usual) only my stupidity that prevented this from working. If I switch it over to the correct baudrate the usb converter does fine. But before I found that out, I did find a computer with a serial port and I did see it working on that too…

Development, Open Source

C Code Commandments

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I’m an old school C programmers guy and I stay true to some of the older and commonly used rules present in many open source and similar projects. Since I sometimes rant about this to people, I thought I’d amuse my surrounding by stating them here for public use/ridicule. Of course heavily inspired by the great and superior The Ten Commandments for C Programmers. My commandments are not necessarily in any prio order.

Thy Code Shall Be Narrow

Only in very rare situations should code be allowed to be wider than 80 columns. I want my two or three windows next to each other horizontally and still see the code fine. Not to mention the occasional loading up in an editor in a 80 columns terminal and that is should be possibly print nicely (for reviews etc). Wide code is also harder to read I think, quite similarly to how very wide texts in web pages etc aren’t kind to your eyes either.

Thou Shall Not Use Long Symbol Names

To be able to keep the code easily readable by human eyes so that you quickly get an overview and understand things, you simply need to keep the function and variable names fairly short. Not to mention that the code gets harder to keep within 80 columns if you use ridiculously long names.

Comments Shall Be Plenty

Yes, this is something we know everyone says and few live up to. In statistical analyzes of my own C code I usually reach around 25-27% comments and I’m usually happy with that amount. Comments should explain what is otherwise not obvious in the code.

No Hiding What’s Really Happening

I’m not a fan of overloaded operators or snazzy macros that do fancy stuff without it being noticeable in the code. It should be clear when reading the code what it does. That’s also one of the reasons you don’t catch me doing a lot of C++ work…

Thou Shalt Hunt Down and Kill Compiler Warnings

Compiler warnings may be significant and in some cases they are not. Either way, it is our duty to silence them at all times. Firstly because it is often simpler to fix the code to not warn than to figure out if the warning is indeed right or not, but perhaps primarily because it makes it harder to see new warnings appearing if the old ones have been left there.

Write Portable Code Unless Forced by Evil

You may first believe that your code will live on forever on this single platform with this single compiler, but soon and very soon you will learn otherwise. Then you will cheer this rule as it makes you consider unaligned memory accesses, assuming byte-order of binary data or the size of your ‘long’ variable type.

Repeat Not, Use Functions

I see a lot of “copy and paste” programming in my daily life and I’ve learned that sooner or later such practices lead to sorrow. If you paste the same code on multiple places it not only makes it repetitive and boring to update it when an API or something changes, more seriously it increases the risk that you address bugs only on one out of many places or that the fix differ etc. It also makes the code larger and thus harder to follow and understand.

Thou Shalt Not Typedef Away Pointers

A really nasty habit to be seen in some source codes is when people use typedefs to define their own types that is simply a pointer to something. Like with ‘typedef struct whatever * whatever_t’. While I’m in general against excessive typedefing, I’m fine with them in many cases but not when used to hide pointers to look like “ordinary” types. It makes code harder to follow.

Defines, no fixed numbers

Code that relies on zero and non-zero can get away without this, but as soon as you start relying on more numbers in the code you must start using #defines or possibly enums to make them appear with names in the code. Using names is more clever than hardcoded numbers since you can avoid having to explain the number in a comment, and of course it’ll be easier to change the actual number in the code at a later point without it being a painful search-and-replace operation.

cURL and libcurl, Development

Some stats on curl development

Counting curl 6.0 and up to curl 7.19.3 we’ve done 78 releases during the 9.4 years it took.

In this time, we’ve mentioned 1259 bugfixes and 389 notable changes.

This makes one bugfix done every 2.7 days. One release done every 43rd day with an average of 16 bugfixes done in each. The longest interval ever between two curl releases was 139 days, back in 2000 when we worked to release the first version 7 release (known as 7.1).

To compare with how our work has been more recently, doing the same math limited to the 20 latest releases only (the 3.3 years since and including 7.15.0) shows that we’re still on 2.7 days per bugfix (although we know that the code base has grown steadily for years) but we’re now on 61 days between releases and 21 bugfixes/release…

All this info and more will be visible on a web page on the curl site soonish, I’m still working on polishing it up.

What other useful or useless but interesting numbers could be extracted from this?

cURL and libcurl, Development, Linux, Network, Web

IETF http-state group created

Over at the IETF another group was just created named http-state (with an associated mailing list) with the specific goal:

Ultimately, the purpose of this group is to create an updated HTTP State Management Mechanism RFC (aka cookies) that will supersede the Netscape spec, RFCs 2109, 2964, 2965 then add in real-world usage (e.g. HTTPOnly), and possibly add in additional features and possibly merge in draft-broyer-http-cookie-auth-00.txt and draft-pettersen-cookie-v2-03.txt.

I’ve joined the list and I hope to follow and participate in this, as I believe the current state of HTTP cookies is a rather sorry mess and the Netscape spec is still what closest describes how cookies work in the wild. Of course I’ll do it with my libcurl experience in my luggage.

While it perhaps would be cool to join the group in more formal way, there’s no way for me to participate in that IETF meeting in San Francisco in March.

Development, Open Source

emacs!

I haven’t said it here before, but I feel I really should. I’ve been an avid emacs user since I started to learn it back in 1991 on emacs 18. I worked at IBM with their RS/6000 machines at the time and I learned C on AIX with emacs as my editor.

To me there was no alternative at that time and I soon learned all the quirks, got used to things and appreciated all the beautiful parts – my fellow colleagues being emacs fans of course helped pushing me into that team. For the fun of it, I’ve checked when vim was started and I’ve learned that it got available for “unix” in 1992. And it probably was quite far away from a real emacs competitor at that time. The vi editor was of course there, but it had no C syntax indent support and it used and still uses that quirky “mode” approach that I’ve never liked.

I came from hacking the C64 to programming Amiga over to AIX and I was used to and liked full-screen editors without any particular mode switching necessary. Still today I find it a bit curious how vi (in the shape of vim) can be this popular given that (in my view) funny concept.

While I do see some of the benefits of XEmacs over GNU Emacs I always disable all menus, icons and toolbars so to me in real-life editing the differences don’t mean a lot, so I tend to go with the plain GNU Emacs.

So, I’ve pretty much used Emacs just about daily at work and in my spare time hacking since then. Even during the few times I’ve been locked in at a windows desktop I’ve managed to get a windows version installed to survive my days!

Thank you emacs team!

Development, IT Politics, Open Source, Security

SSL certs crash without trust

Eddy Nigg found out and blogged about how he could buy SSL certificates for a domain he clearly doesn’t own nor control. The cert is certified by Comodo who apparently has outsourced (parts of) there cert business to a separate company who obviously does very little or perhaps no verification at all of the buyers.

As a result, buyers could buy certificates from there for just about any domain/site name, and Comodo being a trusted CA in at least Firefox would thus make it a lot easier for phishers and other cyber-style criminals to setup fraudulent sites that even get the padlock in Firefox and looks almost perfectly legitimate!

The question is now what Mozilla should do. What Firefox users should expect their browser to do when HTTPS sites use Comodo-verified certs and how Comodo and their resellers are going to deal with everything…

Read the scary thread on the mozilla dev-tech-crypto list.

Update: if you’re on the paranoid/safe side you can disable trusting their certificates by doing this:

Select Preferences -> Advanced -> View Certificates -> Authorities. Search for
AddTrust AB -> AddTrust External CA Root and click “Edit”. Remove all Flags.

Development, Linux, Network

10G and Direct Cache Access

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As some of you might know, I currently work with a client doing 10G network stuff. 10G as in 10 gigabit/second Ethernet. That’s a lot of data. It’s actually so much data it’s hard to even generate network loads of this magnitude to be able to do good tests, as a typical server using SATA harddrives hardly fills a one gigabit pipe due to “slow” I/O: ordinary SATA drives don’t even reach 100MB/sec. You need RAID solutions or putting the entire thing in RAM first. So generating 10 gigabit network loads thus requires some extraordinary solutions.

Having a server that tries to “eat” a line speed 10G is a big challenge, and in fact we can’t do it as 1.25 GB/sec is just too much and yet we run a quad-core 3.00GHz Xeon thing here which is at least near the best “off-the-shelf” CPU/server you can get at the moment. Of course our software does a little bit more with the data than just receiving it as well.

Anyway, recently I’ve been experimenting with 10G cards from Myricom and when trying to maximize our performance with these beauties, I fell over the three-letter acronym DCA. Direct Cache Access. A terribly overused acronym consisting of often-used words make it hard to research and learn about! But here’s a great document describing some of the gory details:

Direct Cache Access for High Bandwidth Network I/O

Summary: it is an Intel technology for delivering data directly into the CPU’s cache, to reduce the bandwidth requirement to memory (note: it only decreases the bandwidth requirement at that moment, not the total requirement as it still needs to be read from memory into the cache, as noted in a comment below). Using this technique it should be possible to drastically reduce the time for getting the traffic. Support for this tech has been added to the Linux kernel as well since a while back.

It seems DCA is (only?) implemented in Intel’s 7300 chipset family which seems to only exist for Xeon 7300 and 7400. Too bad we don’t have one of these monsters so I haven’t been able to try this out for real yet…

Currently we can generate 10G network loads using two different approaches: one is uploading a specially crafted binary blob embedded with the FPGA image to a Xilinx-equipped board with a 10G MAC that then can do some fiddling with the packages (like increasing a counter) so that they aren’t all 100% identical. It makes a pretty good load test, even if the traffic isn’t at all shaped like the “real” traffic our product will receive. Our other approach has been even less good: upload a custom firmware to the network card and have that send the same Ethernet frame… This latter approach didn’t get better because it was a bit too complicated and badly documented on how to make a really good generator out of it. Even if I liked being able to upload custom code to my network card! 😉

Allow me to also mention that the problems with generating 10G is with small packet sizes, like 100 bytes or so as the main problem in the hardwares seem to the number of packets, not the payload part. Thus it is easier to do full line speed with 9000 bytes packets (jumbo frames) than the tiny ones we are likely to get when this product is in use by customers in the wild.

Update: this article was written in 2008. Please note that many things may have changed since then.