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I am trying to use Portaudio. For a start, I'd like to run the tests programs included with the distribution. After I copied the header portaudio.h and libportaudio.a to the test directory, I managed to compile successfully patest_sine8.c with:

$ g++ -o test1 patest_sine8.c -lrt -lm -lpthread -lasound libportaudio.a

When I run the program the output is the following:

PortAudio Test: output signed 8 bit sine wave.
ALSA lib setup.c:548:(add_elem) Cannot obtain info for CTL elem (MIXER,'AC97 2ch->4ch Copy Switch',0,0,0): No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.surround21
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.surround21
ALSA lib setup.c:548:(add_elem) Cannot obtain info for CTL elem (MIXER,'AC97 2ch->4ch Copy Switch',0,0,0): No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.surround41
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.surround50
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.surround51
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.surround71
ALSA lib setup.c:548:(add_elem) Cannot obtain info for CTL elem (PCM,'IEC958 Playback PCM Stream',0,0,0): No such file or directory
ALSA lib setup.c:548:(add_elem) Cannot obtain info for CTL elem (PCM,'IEC958 Playback PCM Stream',0,0,0): No such file or directory
ALSA lib setup.c:548:(add_elem) Cannot obtain info for CTL elem (PCM,'IEC958 Playback PCM Stream',0,0,0): No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.hdmi
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.hdmi
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline
ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred
ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred
ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred

Sound does comes out of the speaker but something is clearly wrong. This is happening on a recent install of Fedora 21 (XFCE) in a virtual machine with VMware. I had to run alsaunmute to get sound after I installed and its ouput is:

/sbin/alsactl: sysfs_init:48: sysfs path '/sys' is invalid

Found hardware: "ENS1371" "Cirrus Logic CS4297A rev 3" "AC97a:43525913" "0x1274" "0x1371"
Hardware is initialized using a generic method

Can somebody point me in the right direction to get Portaudio working?

alexandre
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  • PortAudio tries to open lots of devices that do not exist. Not suppressing these messages is a bug in PA. – CL. Dec 18 '14 at 18:49
  • Okay, thanks for the reply. But there's something I should have made more clear, the message: `ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred` keeps being printed on the terminal until I hit Ctrl+C to exit the program. I don't know what that means. – alexandre Dec 18 '14 at 19:43

2 Answers2

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when a sound device is active, data is transferred continuously between the hardware and application buffers. In the case of data capture (recording), if the application does not read the data in the buffer rapidly enough, the circular buffer is overwritten with new data. The resulting data loss is known as overrun.

repost from: Internet， searching by google. Sorry that I forgot the website.(_)!

Allen Cheung
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  • Welcome to [so]. It appears that this text is from another source. If that is indeed the case, you should quote the text and provide attribution as stated in the [referencing guidelines](http://stackoverflow.com/help/referencing). Also, it's better to also include your own explanation instead of merely quoting another source. For more information, see [answer]. Thanks! – Qantas 94 Heavy Feb 09 '15 at 13:21
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Sound Buffers and Data Transfer

A sound card has a hardware buffer that stores recorded samples. When the buffer is sufficiently full, it generates an interrupt. The kernel sound driver then uses direct memory access (DMA) to transfer samples to an application buffer in memory. Similarly, for playback, another application buffer is transferred from memory to the sound card's hardware buffer using DMA.

These hardware buffers are ring buffers, meaning the data wraps back to the start when the end of the buffer is reached. A pointer is maintained to keep track of the current positions in both the hardware buffer and the application buffer. Outside of the kernel, only the application buffer is of interest, so from here on we discuss only the application buffer.

The size of the buffer can be programmed by ALSA library calls. The buffer can be quite large, and transferring it in one operation could result in unacceptable delays, called latency. To solve this, ALSA splits the buffer up into a series of periods (called fragments in OSS/Free) and transfers the data in units of a period.

During playback, if the application does not pass data into the buffer quickly enough, it becomes starved for data, resulting in an error called underrun. The ALSA documentation sometimes refers to both of these conditions using the term XRUN. Properly designed applications can minimize XRUN and recover if it occurs.

Allen Cheung
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