2010/2/2 pl bossart <bossart.nospam@xxxxxxxxx> > > I don't think that there have been no progress. The queued samples can be > > stored to runtime->delay now, so snd_pcm_delay() returns a correct value. > > > > The snd_pcm_rewind() and snd_pcm_forward() functions should operate in > the > > ring buffer and it's ok. See the USB driver for an example. Just add > support > > for runtime->delay to the lowlevel drivers and use snd_pcm_delay() > correctly > > in the user space and everything will work as expected. > > > > In other words - for hardware with large FIFOs, the runtime->delay should > be > > used for queued samples and the hw_ptr in the ring buffer should be > > increased as soon as the FIFO is filled with samples from the ring > buffer. > > Thanks Jaroslav. > I was under the impression that the runtime->delay indicated the time > needed for transmission and D/A. If this is intended to be the queued > samples, then it plays the same role as my 'fifo' proposal. There are > several consequences though: > - This means rewind() can only happen within the ring buffer, and all > samples previously queued will be played as is. > - the 'only' change is to make sure the hw_ptr reported in .pointer is > NOT the number of samples pushed out to the interface. hw_ptr should > really represent the next read position in the ring buffer, this isn't > uniform across drivers. This means for example that the HDAudio > implementation needs to modified so that the LPIB value is increased > with runtime->delay. > - How do you specify the time for transmission and D/A, so that > applications can know when a sample will actually be played. With your > explanation the applications can only know when a sample will be > pushed out, there is an additional latency not accounted for. > Thanks for your feedback. > - Pierre > > if snd_xxx_pointer call back return the next read position , the hw_ptr will always be multiple of PCI/PCIe brust size _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
