On Tue, 15.04.08 14:19, Takashi Iwai (tiwai@xxxxxxx) wrote: > > As far as I understood there are a few soundcards around where > > the playback sample index is only known each time the hw changes to > > the next fragment. It would be good to know about this, to tweak the > > time interpolation in timer-based scheduling. > > We may add some hints to the PCM information, but I think maybe this > isn't only the question about granualrity. For example, on some > hardwares, the query of the current position costs much due to the > hardware design. What is "much" if I may ask? > > > Documentantion - if you ask specific questions, we try to update > > > documentantion for other developers.. unfortunately, saying that whole > > > documentantion is bad is not productive > > > > Sorry. I'll make sure I'll ask for clarifications more clearly on > > alsa-devel from now on. > > > > Here's my first batch of questions: > > > > I am not sure I get what the "transfer align" is about. > > Just ignore, this is obsoleted in the latest version :) Please remove from the docs, then! Also the part in the "Managing parameters" chapter in the PCM introduction text. > > It is not clear how snd_pcm_update_avail() and snd_pcm_hwsync() > > actually play together, why they exist at all, and how exactly the > > optimization they are apparently useful for should be used. > > The detailed description is found in PCM documentation. Uh, and that's the part I don't get. I did read it, and didn't get it. What exactly does _hwsync() do that _update_avail() doesnt? > > It would be good to have an explanation what a "card", what an "id", > > what a "name", what a "device" and what a "subdevice" actually refers > > to, with examples. > > The card (index) is the index number of the sound card instance. > Each card has an id string and name string(s). > One card instance may have several belonging components. And each > component has (usually) a device index. Some components (e.g. PCM or > rawmidi) can have multiple subdevices (or substreams). Each subdevice > has a subdevice index. The question remains: what exactly is is a "device" and what is a "subdevice"? Examples? For a while I thought that for those sound cards wich can output to SPDIF and analog at the same time we have two different device indexes, but a single card index. However, for my HDA card that is listed in /proc/asound/pcm as "04-00 ALC882 Analog" and "04-01 ALC882 Digital", aplay -L suggests to use "ec958:CARD=Intel,DEV=0" for spdif and "front:CARD=Intel,DEV=0" for analog -- both times with DEV=0! Since then I have no idea what devices, subdevices and stuff should actually be. So again, what exactly qualifies subdevices? Do they share a single crystal? Are they usually combined for multi-channel output? What's the story? > > regarding hw params: What exactly is "double buffering", > > "sample-resolution mmap", "block transfer", "batch", "sync_start" , > > "fifo_size", "subformat", "export buffer", "min align"; > > Most of them can be ignored, at least for PA :) I'd love to get rid > of most of them in future, too. Really? "block transfer" sounds to me like something that would be interesting for mmap playback for cases where i randomly seek around in my mmap buffer, with frame granularity. Which is exactly what I do all the time in PA. > > why there is a > > need for a seperate can_pause() and can_resume()? > > can_pause() means the ability to pause/restart the stream. > > can_resume() means the ability to resume the suspended/hibernated > stream by the driver natively. Uh. This has very confusing naming. > > regarding sw params: What exactly is a "boundary"? Difference between > > tstamp modes? > > The boundary defines the limit PCM position (frames) can reach. When > the PCM position reaches to the boundary size, then it backs to 0 at > next. The boundary size is aligned to the buffer size, and it's not > LONG_MAX (although close to it). But what is this interesting for? I mean, I cannot read the raw hardware pointer index anyway from ALSA, so why should I care? Or is it all for the case where I create a *major* buffer underrun with disabled stop_threshold and the value of _update_avail() keeps increasing but eventually wraps around? > > how do silence_size and silence_threshold relate? > > The PCM driver core has a feature to clear the samples automatically > at each period elapse call. The silence_size and silence_threshold > defines this behavior. But in which way? Please elaborate! > > What is snd_pcm_xrun_t useful for? (I think it is obsolete, should > > also be removed from docs, then) > > Right. Maybe should be classified to the section "obsoleted > functions". A part of the problem is that the reference document is > generated via doxygen, and it seems a bit confusing to arrange the > sections in a single file. You can use stuff like \cond in doxygen to hide certain parts of the API pretty easily. > > Why is snd_pcm_scope included in the normal PCM docs? > > I guess it was thought it'd be pretty useful. Maybe the plugin is useful. But why is it part of the API docs? Thanks, Lennart -- Lennart Poettering Red Hat, Inc. lennart [at] poettering [dot] net ICQ# 11060553 http://0pointer.net/lennart/ GnuPG 0x1A015CC4 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
