A misc weekend

So today is the first week without Gentoo work for me. I admit I feel a bit disappointed, I used to do a lot of stuff and now that I can’t do them anymore (for my choice too), I feel like I’m useless. But I’m resisting the temptation to feel my overlay with a lot of ebuilds for the bumps that I would have done myself previously.

First of all, I wish to thank the anonymous “bla” who commented on my previous post about the lack of analysers for the usbmon output, suggesting me Wireshark. I really didn’t know they were working on supporting USB sniffing, and yes that is nice and stops me from deciding to write an analyser myself. Unfortunately, the current weekly snapshot of libpcap and the current subversion trunk of Wireshark does not get along well together: they simply don’t allow me to sniff at all, I get a series of errors instead.

Talking about the Chinese adapter, I found something on their site but I’m not really sure if it’s a specification or simply a description of the driver interface. Nonetheless, I’ve been able to identify a few patterns in the logs I was able to get with usbmon (analysed by hand), and I now know two major type of commands that are sent to the device: a pair of set and get commands used to set and get a 16 bit word out of at least three «registers»… I’m not sure if they are registers at all, they only are three 16-bit words which have another 16-bit word assigned to them, and which is set and get with some vendor-type requests. Unfortunately, I haven’t been able to get a hold of their actual meaning yet.

I’ve also found a sort of “commit” request, or a “get internal status” command, that tells me I haven’t initialised the device correctly yet: when handled by the Windows drivers, this request always return 0x9494, while here it returns values like 0xf4f4 or similar, never the actual 0x9494 word I’m expecting.

I didn’t work on Rust in the past few days but I have been thinking a lot about it, as David is being the first user of it, and submitted me a few reports of features currently missing, which I didn’t think of before, namely support for multiple constructors, and proper support for sub-classes. I haven’t worked on this yet, but I’ll do soon. He also provided me a patch that I merged, but I’ll have to write a series of testcase for that too, so that I can actually be sure that Rust continue behaving as needed.

Today I also decided to look a bit more on xine, as lately I’ve been neglecting it a lot. I’ve tried to cleanup my Wavpack demuxer a bit more, and I just finished a Valgrind (massif) run while playing two wavpack files one after the other. The results are somewhat interesting: xine does not leak memory, as the memory consumption remains constant between the two playbacks, but it also seems to allocate about ten megabytes of memory in _x_video_decode that are not used at all, as I’ve disabled the effect plugins, and so there should be no video at all. About seven more megabytes are wasted in the overlay handling, which also shows that the video output is not correctly disabled while playing audio tracks, with xine-ui at least.

I’ll be running a callgrind now also to test where time is actually lost, it’s good now that I have KCacheGrind displaying properly the callgraph, thanks to Albert Astals Cid (TSDgeos from KDE). One thing that I’m afraid of is that xine does not really have good performances on lossless files because it uses too small buffers, at least by default; I have this doubt because while mp3s play mostly fine – with mad decoder, not FFmpeg’s – it skips a lot for both Flac and WavPack files. This is especially seen when you run it through Valgrind, as the code is obviously slowed down and shows the need for improvements.

If only there was support in ruby-prof for Valgrind-style output to analyse the output with KCacheGrind, I could be improving Rust too. But that will have to wait I’m afraid.

Oh well.

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