Linux-audio-dev

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7501 discussions

by lieven moors

< However you can also use them to < implement circular FIFOs for example, which is a trick used all the < time in audio as well as in kernel programming. For anyone interested... The Effo libraries seem to have a fair choise of lock-free queue and ringbuffer implementations in the addon project: http://code.google.com/p/effoaddon/ But I have to admit that i find these concepts quite confusing...

15 years, 6 months

Atomic Operations

by Gabriel M. Beddingfield

Recently on this list, Paul referred to an "atomic integer swap" and an "atomic pointer swap." This was a new concept to me (and possibly others), and this e-mail shares what I've learned. If you access a variable from multiple threads -- even a built-in variable like 'int', it is important to control access to the variable with a mutex, semaphore, or an atomic operation. Alexander Sandler, on his blog, wrote a couple of good articles on the subject: "Do you need a mutex to protect an int?" http://www.alexonlinux.com/do-you-need-mutex-to-protect-int "Multithreaded simple data type access and atomic variables" http://www.alexonlinux.com/multithreaded-simple-data-type-access-and-atomic… The first article contains code that calculates a wrong answer on multiprocessor machines. I've attached a similar example that will even fail on a single-processor machine. There is a wealth of reading material on using Mutexes and Semaphores. However, information on atomic operations appears to be sparse and hard-to-follow. So, here's what I've found: + At the moment, there is no built-in support in C/C++ for atomic operations. You will need to use a library, compiler extension, or write your own in assembly code. + The GCC compiler has the built-in __sync_*() functions[1] that provide atomic operations. Note that the attached example is using this. + glib provides the g_atomic_*() functions[2]. + Qt 4 has the q_atomic_*() functions.[3] While they are accessible, they are /not/ a part of their stable, public API. + The next version of ISO C++ (code name c++0x) is expected to have support for atomic operations (E.g. the std::atomic<T> template) and memory barriers. It may even require that all built-in types be atomic. + In the x86 instruction set, these are usually implemented using the 'LOCK' instruction prefix.[5] When using atomic operations, perhaps the best advice I found is near the end of Sandler's second article: "When using atomic variables, some extra precautions have to be taken.... There is nothing that prevents you from incrementing value of the atomic variable with __sync_fetch_and_add() as I just demonstrated and later in the code doing same thing with regular ++ operator. "To address this problem, I strongly suggest wrapping around atomic functions and variables with either ADT in C or C++ class."[4] Peace, Gabriel [1] http://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Atomic-Builtins.html [2] http://www.gtk.org/api/2.6/glib/glib-Atomic-Operations.html [3] http://doc.trolltech.com/4.3/atomic-operations.html See also the Qt header file QtCore/qatomic_i386.h, and its brothers. [4] http://www.alexonlinux.com/multithreaded-simple-data-type-access-and-atomic… [5] http://siyobik.info/index.php?module=x86&id=159

15 years, 6 months

ladspavst.linuxaudio.org site is going offline

by Ivica Ico Bukvic

All ladspavst users/contributors, A ladspavst visitor has brought to my attention that the ladspavst.linuxaudio.org has been spammed for quite some time, rendering a page into useless goop of spam. This is mainly due to lack of moderation. As a result, I've no other choice than to take the site offline until further notice. If you or someone you know is supposed to take care of this site, please contact me and we'll figure out the best way to bring this site back online. Until that happens, the site will remain offline. Best wishes, Ivica Ico Bukvic, D.M.A. Composition, Music Technology Director, DISIS Interactive Sound & Intermedia Studio Director, L2Ork Linux Laptop Orchestra Assistant Co-Director, CCTAD CHCI, CS, and Art (by courtesy) Virginia Tech Dept. of Music - 0240 Blacksburg, VA 24061 (540) 231-6139 (540) 231-5034 (fax) ico(a)vt.edu http://www.music.vt.edu/faculty/bukvic/

15 years, 6 months

Maximum size of SysEx messages in JACK MIDI and ALSA sequencer

by Dominic Sacré

Hi, I'm wondering what the size limit is for SysEx messages in the JACK MIDI and ALSA sequencer APIs. My observations so far: In JACK MIDI, a SysEx message can be as large as the MIDI port buffer, which in turn has the same size as an audio buffer for one period. This is assuming that there are no other events transmitted on the same port during the same period. Is this correct? Or are applications somehow expected to handle larger SysEx messages split over multiple periods? In the documentation of the ALSA sequencer API, I couldn't find any mention of an upper limit. Some sources suggest that ALSA splits SysEx messages into chunks of 256 bytes, but from my own attempts at sending larger messages, it seems the limit is actually somewhere around 5500 bytes. Unfortunately ALSA doesn't seem to report an error when I try to send larger chunks, instead the messages just disappear. Can anyone shed some light on how to handle larger SysEx messages correctly? Thanks, Dominic

15 years, 6 months

libsndfile-1.0.21

by Erik de Castro Lopo

Hi all, Yesterday I released version 1.0.21 of libsndfile. Its available here: http://www.mega-nerd.com/libsndfile/#Download Main changes for this version are: * Add a couple of new binary programs to programs/ dir. * Remove sndfile-jackplay (now in sndfile-tools package). * Add windows only function sf_wchar_open(). * Bunch of minor bug fixes. Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

15 years, 6 months

Hi,,go to Dopcity !!

by Γιάννης Γράβεζας

dear www.dopcity.com ，It can be a good place for select christmas gift! let's go!

15 years, 6 months

Possible snd_pcm_hw_params_set_buffer_time_near() gotcha

by Mario Lang

Hi. I just happened to stumble about a (what I call) pretty subtle bug in typical ALSA PCM code: root@fzidpc73:/tmp# cat test.c #include <stdio.h> int main() { int period = 1024; int nperiods = 3; int rate = 96000; unsigned buffer_time = 1000000*period*nperiods/rate; printf("%d\n", buffer_time); } root@fzidpc73:/tmp# ./test -12739 root@fzidpc73:/tmp# sed -i -e 's/int rate/unsigned int rate/' test.c root@fzidpc73:/tmp# gcc -o test test.c root@fzidpc73:/tmp# ./test 32000 I.e., don't trust this boilerplate formula blindly. -- CYa, ⡍⠁⠗⠊⠕

15 years, 6 months

Re: [LAD] First L2Ork track now available

by Ivica Ico Bukvic

> amount of positive feedback and it has been truly hart-touching to learn Umm, that should read "heart-touching"... DOH! :-) Ico

15 years, 6 months

First L2Ork track now available

by Ivica Ico Bukvic

Dear fellow FOSS enthusiasts, Last week's L2Ork debut was a great success with the performance hall packed and people standing in the back. We've had a tremendous amount of positive feedback and it has been truly hart-touching to learn that people genuinely cared about and were moved by what we had to share. As some of you may be already aware, our story also made the Slashdot and our server has received close to a half a million hits since its posting. Likewise, we've been featured on regional TV channels as well as various international news outlets. As our thanks to all who have so generously supported us both in person and through the endless corners of the internet, we've posted a track from our weekend recording session. "Citadel" is a piece for soprano and L2Ork that uses a poem by Ivan Gundulic, a famous Croatian poet from the Baroque era. The piece was recorded in a beautifully reverberant Burruss rotunda on the Virginia Tech campus. No post-processing has been applied to the recording beyond a minor eq to soften lows. To listen please visit http://l2ork.music.vt.edu/main/ and click on the Media->Jukebox, or simply click on the link in what is currently the top post on the L2Ork blog. Once again, thank you all for your kind support. We will be starting a public l2ork-dev list soon, so if you wish to contribute, participate, or start your own L2Ork, please do not hesitate to join in on the discussion. Likewise, should you feel compelled to leave a comment, please feel free to do so on our jukebox page (no registration required). Best wishes, Ivica Ico Bukvic, D.M.A. Composition, Music Technology Director, DISIS Interactive Sound & Intermedia Studio Director, L2Ork Linux Laptop Orchestra Assistant Co-Director, CCTAD CHCI, CS, and Art (by courtesy) Virginia Tech Dept. of Music - 0240 Blacksburg, VA 24061 (540) 231-6139 (540) 231-5034 (fax) ico(a)vt.edu http://www.music.vt.edu/faculty/bukvic/

15 years, 6 months

Re: [LAD] jack ringbuffer question

by lieven moors

Thanks for pointing that out to me. I've started a version which uses atomic pointer exchange, and this is something I wasn't aware of. I think it shouldn't be a problem right now, as I keep the objects I use in memory, and I don't need the reaction of the program to the pointer swap to be a realtime operation. thanks again for your reply, lieven

15 years, 6 months

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Linux-audio-dev