[alsa-devel] usleep() and nanosleep() timings seem inaccurate using ALSA
tiwai at suse.de
Thu Mar 29 12:42:14 CEST 2007
At Thu, 29 Mar 2007 17:46:38 +0800,
Carlo Florendo wrote:
> Good Day!
> After studying the intricacies of MIDI, I ended up writing an
> implementation of the MIDI protocol and file format.
> I then studied the ALSA sequencer API to be able to control a synthesizer
> keyboard and play MIDI files. I've used aplaymidi, aconnect, arecordmidi,
> and all those great ALSA utilities. They're very good!
> However, I wanted to have a simple ncurses based, command line MIDI
> sequencer meant for small Linux distributions such as DSL or Trustix so I
> began to write a command line sequencer using ALSA. I've encountered one
> problem about using usleep() and nanosleep() especially in 2.4 kernels.
You cannot get a small sleep usually on user-space processes.
Usually, usleep() is implemented with select/poll and its timeslice is
defined by HZ in kernel config. In most cases, it's HZ=100, 250 or
1000 while 2.4-i386 kernel supports only HZ=100. That is, the least
sleep time is 10ms no matter what value you pass to usleep().
This can be overcome by using a realtime schedule class and priority
like JACK does.
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