From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Iwai Subject: Re: Re: [PATCH] emu10k1: add interval timer support Date: Fri, 24 Sep 2004 15:43:30 +0200 Sender: alsa-devel-admin@lists.sourceforge.net Message-ID: References: <1095405566.19045.35.camel@krustophenia.net> <1095795402.13220.21.camel@krustophenia.net> <1095865270.498.20.camel@krustophenia.net> Mime-Version: 1.0 (generated by SEMI 1.14.5 - "Awara-Onsen") Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <1095865270.498.20.camel@krustophenia.net> Errors-To: alsa-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , List-Archive: To: Lee Revell Cc: Jaroslav Kysela , alsa-devel List-Id: alsa-devel@alsa-project.org At Wed, 22 Sep 2004 11:01:11 -0400, Lee Revell wrote: > > On Wed, 2004-09-22 at 06:16, Takashi Iwai wrote: > > At Tue, 21 Sep 2004 15:36:42 -0400, > > Lee Revell wrote: > > > > > > I am using kX ASIO as a reference for how multichannel PCM should work. > > > From the application's point of view, this looks like 16 mono channels. > > > In the mixer, for each of the 16 ASIO channels you have 4/8 drop down > > > boxes to set the FX send destinations and 4/8 sliders to set the send > > > amounts. By default ASIO 1 goes to FXBus channel 0, 2 goes to FXBus 1, > > > etc. Multiple applications can open the same ASIO channel and the > > > driver will allocate additional voices with the same send routing. > > > > > > I think that the ALSA equivalent would be to have another device with > > > channels_min=channels_max=1, and 16 substreams for which the routing > > > would be controlled with the mixer; if multiple applications open the > > > same substream we would allocate another voice. You would call > > > snd_pcm_period_elapsed for each of these streams in the handler for the > > > EFX capture interrupt. All applications using this device must use the > > > same period size settings, as in the Windows driver, the only setting in > > > the ASIO control panel is the latency aka buffer size. > > > > > > You would then use an .asoundrc plugin that would look like a 16 channel > > > PCM device, and would consist of 16 mono channels, hw:x,x,0 through > > > hw:x,x,15. > > > > Maybe I didn't get your point, but why not simply provide a 16-channel > > non-interleaved device? > > > > Several reasons. With the kX driver, if I am using a ReWire host like > Ableton Live, and I want to use an app that is not ReWire capable, I > would have the app output to two extra ASIO channels, say 10 and 11, > and Live can use these as inputs like any other physical input. Live > would then output to ASIO 1/2 (front), ASIO 3/4 (rear), and ASIO 5/6 > (headphones/prelisten). It seems like the best way to do this in ALSA > is to have the driver support a bunch of mono channels and use alsalib > plugins to make multichannel devices out of these. > > How would I open only channels 10 and 11 with one app and 1-6 with > another using a single 16 channel device? It's doable to implement the multi-channel non-interleaved PCM with multi open. But even in this case, we provide eventually 16 substreams, so perhaps providing 16 mono substreams would be easier to implement (at least for the kernel driver). Regarding the efficiency (latency), there will be no difference between the multi-channel and multi-substream implementations. In the latter case, we can use linked substreams, as you already mentioned. > Also, it seemed like it would be easier to handle mmap with a bunch of > mono streams, but maybe I don't understand the mmap completely. The OSS > driver for example does not support mmap for multichannel PCM. This doesn't matter on ALSA. The mmap of a multi-channel non-interleaved substream is handled as well as a normal substream. The snd_pcm_mmap_begin() and commit() hide the difference well. Takashi ------------------------------------------------------- This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170 Project Admins to receive an Apple iPod Mini FREE for your judgement on who ports your project to Linux PPC the best. Sponsored by IBM. Deadline: Sept. 24. Go here: http://sf.net/ppc_contest.php