On Fri, Jul 03, 2020 at 08:16:26AM +0200, Tanjeff Moos wrote: > > Anyway, when using alsa-lib application for the purpose, you should pay > > enough attention to which API is used since alsa-lib includes several > > abstractions of API for control element set in each level: > > > > * Lower abstraction (snd_ctl_xxx) > > * Higher abstraction (snd_hctl_xxx) > > * Setup control interface (snd_sctl_xxx) > > * Mixer interface (snd_mixer_xxx) > > * Simple Mixer interface (snd_mixer_selem_xxx) > > I find this quite confusing. If I could change a volume control using any of > those interfaces, then I don't understand when to use which interface. I'm > sure that there is good reasoning for each of them, but unfortunatly the > documentation has very little information about these concepts. So do I. I can imagine that the toughness of work to design good abstraction for the control feature... > Anyway, I will stick to the lower abstraction which serves my needs. In the > worst case I will do more work than necessary ;-) > > > The configuration space of alsa-lib affects Setup control interface > > and Mixer interface. On the other hand, it doesn't affect the > > lower/higher abstraction. The amixer is a kind of application to use > > 'snd_hctl_xxx', 'snd_mixer_xxx', and 'snd_mixer_selem_xxx'. > > So the controls offered by CTL/HCTL are determined by the driver? And SCTL, > MIXER and MIXER_SELEM are influenced by user space config files? Yes, as long as I know. HCTL abstraction nearly equals to 'CTL + cache mechanism for control elements + event notification callback'. However in some cases of addition/removal control element set from user space[1], it hits assert and aborts programs with panic. SCTL/MIXER/MIXER_SELEM features includes extra filter logic for control elements with the configuration. They're specialized to usual channel of audio; e.g. stereo, surround sounds. It's functional as long as using usual sound devices such as stereo speakers. On the other hand, they can handle just a part of the channels when handling control elements for exceptional multi-channel of audio for recording equipments. I guess that your case is the latter. > > When you'd like to communicate to kernel land implementation without any > > effects of alsa-lib's configuration space. it's better to use the lower/higher > > abstractions. As long as I've used, 'qashctl' in QasTools[4] is good GUI > > application for this purpose. It's written with Qt5 and seems to be helpful > > for your work in both of GUI programming and control elements handling. > qashctl is indeed very helpful, thank you! As being said, I'll stick to CTL. > > Thank you very much for your advice! Quashctl is pretty good tool for the purpose as long as I know. I wish for someone to develop similar functional tool with CUI or TUI... [1] for example, below test program can abort pulseaudio when removing added control element set: https://github.com/alsa-project/alsa-lib/blob/master/test/user-ctl-element-set.c Regards Takashi Sakamoto
