Takashi Iwai wrote: > 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. > Clear enough :) Thanks for the pointers. Best Regards, Carlo -- Carlo Florendo Softare Engineer/Network Co-Administrator Astra Philippines Inc. UP-Ayala Technopark, Diliman 1101, Quezon City Philippines http://www.astra.ph -- The Astra Group of Companies 5-3-11 Sekido, Tama City Tokyo 206-0011, Japan http://www.astra.co.jp _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
