On Sun, 7 Dec 2003, Arve Knudsen wrote:The user is allowed to choose between devices, but its also good to be able to display information about the different units. Like its normal in Windows audio applications to choose between available devices in the system and their respective channels. Are you saying this is a bad thing?
I'd like to be able to query the capabilities (number of channels, buffer
size etc.) of ALSA devices in the system, even if they should be in use by
some other process. The only current way to probe device capabilities is
to open a pcm, and use snd_pcm_hw_params, correct? At least this is my
current approach, but I'd like to query the devices without first
acquiring exclusive access. If there is currently no way around acquiring
a device for querying, maybe this requirement could be loosened in a
future version of ALSA?
Nope. You ask for runtime information. This information can change due various hardware contraints so we cannot give you an useful information without blocking the device.
Anyway, auto-probing for devices is a bad idea. Let user to choose the device (hw:X,Y or plughw:X,Y or some "abstract" name in a dialog box) yourself. The hw:X,Y numbers can be determined using the control API in a non-blocking way.
Isn't this pretty much what I'm asking for? I don't care how its done, I would just like to obtain available information in some civilized manner (so I can gather info during initialization) :) Speaking of information, I wouldn't mind some info from each driver about supported period sizes, like ASIO has a way of obtaining buffer granularity I think. Could be useful for determining a common period size if a full-duplex stream consists of two different devices.I think that we should provide the list of devices with a description via some interface in alsa-lib.
Regards
Arve Knudsen
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