On Fri, Nov 5, 2010 at 1:58 PM, Clemens Ladisch clemens@ladisch.de wrote:
Adam Rosenberg wrote:
On Fri, Nov 5, 2010 at 10:31 AM, Clemens Ladisch clemens@ladisch.de wrote:
How much CPU does "aplay -D hw -t raw -f dat /dev/zero" use?
I do not know how to calculate CPU usage for a given process.
The time utility (if you have it) measures both elapsed and actually used CPU time.
I am not sure how to interpret this, but I told aplay to play for 3 minutes from /dev/zero and here are the results: root:/> time aplay -d 180 -D hw -t raw -f dat /dev/zero Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo real 3m 0.10s user 0m 0.22s sys 0m 8.48s
For the audio playback I am polling the streams using snd_pcm_avail_update() and then writing the number of frames available using snd_pcm_writei().
And what does your program do when avail_update returns 0 frames?
If it returns 0 then I do not write any frames. I then check the next stream. This continues in an infinite loop.
You cannot write data faster than it's playing; the audio ring buffer has a finite size.
You would have a problem if the processing and/or the driver would make everything so slow that you wouldn't be able to write new data to the device fast enough, which would result in an buffer underrun. Does this actually happen?
I am currently writing the decoded mp3 data to a buffer in RAM so that the program is decoding the mp3 data as fast as it can. I then run the audio process separately and just play silence. I am doing this so that I can tell how much time is being spent decoding mp3 data and processing audio data so that I know how much time remains for other tasks. From the times I have calculated I can tell that a buffer underrun would occur frequently if I was actually writing the decoded mp3 data to the pcm streams.
-Adam