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.
Takashi