Nodal Point

This blog goes to github with all its posts. Cheers Tumblr! I'll keep the account to read others, but won't post. New blog will be accessible via http://exocortex.madfire.net.

I've ported events, sequencers and event-based communication primitives from Nemesis. It's a little bit messy at the moment (mostly because of mixing C and C++ concepts in one place), but I'm going to spend the autumn time on cleaning it up and finishing the dreaded needs_boot.dot dependencies to finally bootstrap some domains and perform communication between them. Obviously, the shortest term plan is timer interrupt, primitive kernel scheduler which activates domains and events to move domains between blocked and runnable queues. There's some interesting theory behind using events as the main synchronization mechanism, described [here](http://research.microsoft.com/pubs/72910/UCAM-CL-TR-361.pdf) in more detail. For the vacation time I've printed some ANSA documents, which define architectural specifications for distributed computation systems and is very invaluable source of information for designing such systems. The full list of available ANSA documents can be found [here](http://www.ansa.co.uk/ANSATech/ANSAhtml/). Good reading.

I needed to quickly check how much of Nemesis support has to be ported over before I can start launching some basic domains. I used a simple shell one-liner to extract NEEDS dependencies from the interface files. It's easy to do in Nemesis because of explicit NEEDS clause in each interface (would be nice to add this functionality to meddler, it also has the dependency information available). Here's the shell one-liner: `echo "digraph {"; find . -name '*.if' -exec grep -H NEEDS {} \; | grep -v "\-\-" | sed 's/ *NEEDS //g' | sed 's@^\./@@' | sed 's/\.if//' | awk -F: '{print $1, "->", $2}'; echo "}" ` This generated a huge [graphic](http://downloads.exquance.com/metta/needs_full.png) with all dependencies, which I then filtered a bit by removing unreferenced entities and culling iteration after iteration. The [resulting graphic](http://downloads.exquance.com/metta/needs_boot.png) is much smaller and additionally has a hand-crafted legend (green - leaf nodes, yellow - direct dependencies of DomainMgr and VP, my two interfaces of interest). This shows I need to work on about 10-12 interface implementations to be able to run domains. And my ticket tracker of choice, bugs-everywhere now has an entry 7df/0fe 'Generate dot files with dependency information in meddler'. Time to sleep.

**Alan Kay** via folklore.org

I've been working on toolchain building script, now at least on Macs it's possible to build a standalone toolchain for building Metta and you can download it and try to build it yourself. All necessary details are descibed on [SourceCheckout wiki page](http://metta.exquance.com/wiki/SourceCheckout). There is followup work to remove dependency on binutils and gcc (gcc will probably go first, then once lld is mature enough I could get rid of ld/gold). Another update is about type system. The operations on type system are implemented now, I can successfully register type information and query it - some examples of that are in the recently released iso image R925. Next up is fixing some of naming context operations so I can actually create and operate hierarchical naming contexts.

Since I've decided to approach the system development from both low-level and high-level perspectives, one of the applications I have in mind for demo purposes is a little console tool which lets you activate various parts of the system, list available services and call operations on available interfaces. Imagine a little tool that allows you to pick a video file, seek it to a particular time and play it frame by frame, then run face recognition on each frame and make a database of recognized faces. Being able to make such applications "mashup style" by just fiddling with text and pictures in the command line should enable people to create more and more interesting tools from the basic building blocks presented by the system. This tool would need to inspect installed interfaces and types of the running components and be able to construct calls to these components directly from the command line. This requires introspection, or the ability to describe structure of objects in the system. At the moment I'm working on the extension of meddler that allows to generate introspection data from the interface IDL. It is generally simple and then the next step would be to somehow register this information in the system when a new interface type is introduced. This is harder and requires some design effort. In the first approach of course only boot image is loaded, so registering types is very simple. Next up is actual introspection interface - how to know what format a particular data type is and how to marshal/unmarshal it for the purpose of interchange and operations calls on interfaces.

Hehe, this is truly amazing museum! The best I've seen lately.

I took three more classes (actually, I took a lot more this time, but they all fell off, still hope to at least watch the videos). So here's the breakdown: [Udacity CS212](http://www.udacity.com/course/cs212) - Design of Computer Programs - a bit boring for me, I usually do all the same stuff as my daily job. Might be interesting to people new in the craft. [Udacity CS387](http://www.udacity.com/course/cs387) - Applied Cryptography - very interesting one, enjoying the theory and application equally. [Coursera Compilers](http://coursera.org/compilers) - Compilers (ha!) - extremely interesting, very practical and exciting course. I'm kinda skipping the quizzes - they are too theoretical and not very interesting, but spend most of my time on actually implementing the lexer and parser and in the future hopefully some code generation and optimizations as well. So far, my favourite course.

IRQ11 enabled. Finished initializing NE2000 with MAC b0:c4:20:00:00:00. Received irq: 0x0000000b Packet transmitted. Packet received. Received packet with status 33 of length 68, next packet at 82 0x004f0064 ff ff ff ff ff ff 28 cf da 00 99 f5 00 10 48 65 ......(.......He 0x004f0074 6c 6c 6f 20 6e 65 74 20 77 6f 72 6c 64 21 00 00 llo net world!.. 0x004f0084 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 0x004f0094 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

Of course, the clang's implementation of setjmp is very generic and uses quite an abstraction of program state, which makes it hardly suitable for the ad-hoc local exception support I'm using. Since my requirements for setjmp were quite simple (just give me back my damn registers and stack frame), I went and implemented a very custom-tailored versions __sjljeh_setjmp and __sjljeh_longjmp which do just what I need. With [that stuff](http://metta.exquance.com/browser/src/runtime/setjmp.s) out of the way, my entire boot sequence now works and I can finally fiddle with more interesting stuff. Type system and introspection, here we go.

I'm done with CS373, having implemented some quite nice algorithms that can be used to real-life robot navigation and after a surprisingly well done final exam (my hopes weren't so high after the AI class, so I'm positively surprised). It was so fun I signed up for two more classes starting April 16. - Applied Cryptography and Design of Computer Programs. Can't wait to have moar edjuukation.

How to stop worrying and love your visualization tools.

(Both these are less of "just lectures" and more of the interactive study class approach)

Now everything boots up until exceptions, at which point I believe the __builtin_longjmp primitive fails. Debugging it.

With the material provided I'm basically ready to build a small self-navigating robot, so I hope my Pololu 3pi will get some use soon.

I've finished my CS373 homework 5 at Udacity - more about that in the next post.