On Jun 12 2017 01:53, Takashi Iwai wrote:
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".
Indeed. It's better.
Regards
Takashi Sakamoto
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
