Hi, Could someone enlighten me about the way alsa-lib / alsa-driver are supposed to work when using mmap mode please? I'm looking at the 1.0.2 code, along with madplay and Linux 2.6.4-rc1.
madplay sets the start_threshold to the size of the buffer, and min_avail to one period size - in much the same way as the alsa-lib test/pcm.c program. However, there appears to be a case where if snd_pcm_write_areas is called with non-period-sized blocks of samples, we end up waiting for the buffer to be emptied without starting the hardware. This can be clearly seen from a couple of fprintf's placed into this function (buffer size 16384, start threshold 16384, min_avail = 2047) snd_pcm_write_areas: offset 0 size 480 snd_pcm_write_areas: avail = e80 avail_min = 7ff size = 480 xfer_align = 1 snd_pcm_write_areas: hw_avail = 3600 start_threshold = 4000 snd_pcm_write_areas: offset 0 size 480 snd_pcm_write_areas: avail = a00 avail_min = 7ff size = 480 xfer_align = 1 snd_pcm_write_areas: hw_avail = 3a80 start_threshold = 4000 snd_pcm_write_areas: offset 0 size 480 snd_pcm_write_areas: avail = 580 avail_min = 7ff size = 480 xfer_align = 1 snd_pcm_write_areas: hw_avail = 3f00 start_threshold = 4000 snd_pcm_write_areas: offset 0 size 480 snd_pcm_write_areas: avail = 100 avail_min = 7ff size = 480 xfer_align = 1 Here, (avail < pcm->avail_min && size > avail) is true, so we end up calling snd_pcm_wait(). However, because hw_avail < start_threshold, we haven't called snd_pcm_start(). Here's the output of the /proc *_params and status files while the device is in this state: /proc/asound/card0/pcm0p/sub0/hw_params:access: MMAP_INTERLEAVED /proc/asound/card0/pcm0p/sub0/hw_params:format: S16_LE /proc/asound/card0/pcm0p/sub0/hw_params:subformat: STD /proc/asound/card0/pcm0p/sub0/hw_params:channels: 2 /proc/asound/card0/pcm0p/sub0/hw_params:rate: 44100 (44100/1) /proc/asound/card0/pcm0p/sub0/hw_params:period_size: 2047 /proc/asound/card0/pcm0p/sub0/hw_params:buffer_size: 16384 /proc/asound/card0/pcm0p/sub0/hw_params:tick_time: 10000 /proc/asound/card0/pcm0p/sub0/status:state: PREPARED /proc/asound/card0/pcm0p/sub0/status:trigger_time: 0.000000000 /proc/asound/card0/pcm0p/sub0/status:tstamp : 1078051902.544283000 /proc/asound/card0/pcm0p/sub0/status:delay : 0 /proc/asound/card0/pcm0p/sub0/status:avail : 256 /proc/asound/card0/pcm0p/sub0/status:avail_max : 0 /proc/asound/card0/pcm0p/sub0/status:----- /proc/asound/card0/pcm0p/sub0/status:hw_ptr : 0 /proc/asound/card0/pcm0p/sub0/status:appl_ptr : 16128 /proc/asound/card0/pcm0p/sub0/sw_params:tstamp_mode: NONE /proc/asound/card0/pcm0p/sub0/sw_params:period_step: 1 /proc/asound/card0/pcm0p/sub0/sw_params:sleep_min: 0 /proc/asound/card0/pcm0p/sub0/sw_params:avail_min: 2047 /proc/asound/card0/pcm0p/sub0/sw_params:xfer_align: 1 /proc/asound/card0/pcm0p/sub0/sw_params:start_threshold: 16384 /proc/asound/card0/pcm0p/sub0/sw_params:stop_threshold: 16384 /proc/asound/card0/pcm0p/sub0/sw_params:silence_threshold: 0 /proc/asound/card0/pcm0p/sub0/sw_params:silence_size: 0 /proc/asound/card0/pcm0p/sub0/sw_params:boundary: 1073741824 -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/ 2.6 Serial core ------------------------------------------------------- SF.Net is sponsored by: Speed Start Your Linux Apps Now. Build and deploy apps & Web services for Linux with a free DVD software kit from IBM. Click Now! http://ads.osdn.com/?ad_id=1356&alloc_id=3438&op=click _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
