On Wed, Nov 10, 2010 at 12:35 PM, Jaroslav Kysela <perex@xxxxxxxx> wrote: > On Wed, 10 Nov 2010, Manu Abraham wrote: > >> testbox ~ # arecord -Dplughw:2,0 >> Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono >> ALSA lib pcm_mmap.c:369:(snd_pcm_mmap) mmap failed: Invalid argument >> arecord: set_params:1041: Unable to install hw params: > > set_params fails, because snd_pcm_mmap (mmap() syscall) failed for your > driver. The configuration space for hw_params is now OK. > > You have to check sound/core/pcm_native.c, if snd_pcm_default_mmap() and > snd_pcm_mmap_data() implementation matches the mmap policy for your DMA > buffer. You may create your own mmap callback - substream->ops->mmap. I didn't yet map the buffers, will check it out. > >> bufsiz=31872 periods=83 bytes=384 > > This looks correct. Frame (in ALSA meaning) is 2 8-bit unsigned samples (you > have forced to use 2 channels in your hw->ops). Thus 192 frames is 384 bytes > for this stream format. Perhaps, your frame is not ALSA frame. 192 came from a mS long capture at 48kHz. > > ALSA frame: channels * sizeof(sample) > >> Now, I wonder what a period really is. I guess I lack the basics here >> .. A basic explanation to the context, >> would be quite helpful. > > Period is just a time after which should the driver acknowledge the > transferred samples. Note that it's preffered to also allow large periods > (if you can set hw to not acknowledge each DMA block transfer). Ok, so period should be the interval at which an IRQ is expected. ie, if i set a buffer size for 40mS, the period should be 40, I guess. That said, what should be a recommended value for period ? If hardware needs to generate an IRQ at the end of each period ? Thanks, Manu _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
