2010/11/2 Pierre-Louis Bossart bossart.nospam@gmail.com
Merged and cleaned patch based on earlier patches posted on alsa-devel by Clemens Ladisch clemens@ladisch.de and Pierre-Louis Bossart pierre-louis.bossart@intel.com
This patch disables period interrupts which are not needed when the application relies on a system timer to wake-up and refill the ring buffer. The behavior of the driver is left unchanged, and interrupts are only disabled if the application requests this configuration. The behavior in case of underruns is slightly different, instead of being detected during the period interrupts the underruns are detected when the application calls snd_pcm_update_avail, which in turns forces a refresh of the hw pointer and shows the buffer is empty.
But PA server set stop threshold to boundary, according to
http://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m___s_w___params.h...
PCM is automatically stopped in SND_PCM_STATE_XRUN state when available frames is >= threshold. If the stop threshold is equal to boundary (also software parameter - sw_param) then automatic stop will be disabled (thus device will do the endless loop in the ring buffer).
The available buffer will not be empty (zero) but negative since device will do the endless loop