On Sun, 11 Jun 2017 08:48:07 +0200, Takashi Sakamoto wrote: > > In design of ALSA PCM core, both of hardware-side and application-side > position on PCM buffer are maintained as a part of information for > runtime of PCM substream. In a view of ALSA PCM application, these two > positions can be updated by executing ioctl(2) with some commands. > > There's an event of tracepoint for hardware-side position; 'hwptr'. > On the other hand, no events for application-side position. > > This commit adds a new event for this purpose; 'applptr'. When > the application-side position is changed in kernel space, this event > is probed with useful information for developers. > > I note that the event is not probed for all of ALSA PCM applications, > because the application-side position is passively maintained in mmap > programming scenario. In this case, applications should be programmed > with ioctl(2) with SNDRV_PCM_IOCTL_SYNC_PTR to commit the application-side > position to kernel land when it operates any PCM frames. Here "should" is no correct choice of word. As you already noted in the cover letter, the notification of appl_ptr in the mmap mode with the status/control mmap is voluntary. So, it's not "should be programmed" but "may be programmed". thanks, Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
