At Fri, 30 Mar 2007 09:53:33 +0800, Carlo Florendo wrote: > > Takashi Iwai wrote: > > 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. > > Ok. I will take that seriously. I've heard about JACK and know it's > popular but I've never used it. Well, I don't mean JACK handles the MIDI in that way but as an example of real-time (audio) application. Basically you have to just set process scehduler class to SCHED_FIFO and raise the priority. Then your process would get invoked as soon as triggered, such as return from poll() events. > In any case, how does aplaymidi (or even timidity) produce the proper > timings using ALSA? (In other words, how does the queue output sounds with > correct timings?) The ALSA sequencer queue is implemented on kernel, so it can have and use more accurate timer sources. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
