Re: [linux-audio-dev] [WIP] hdsposc

thomas charbonnel <thomas@email-addr-hidden> writes:

>> Hi.
>>
>> Since I finally ordered my Multiface, I also started to write
>> a small program which I am going to need since hdspconf and hdspmixer
>> are both GUI only.
>>
>> The idea:
>> hdsposc will offer the RME mixer and the metering functionality
>> via OSC.
>>
>> Why do I write this mail? I'd like to know if someone else
>> could also make use of this tool. If so, I'd like to hear
>> your input what you'd want to exactly do with it. If no one responds,
>> I'll save coding time by ONLY implementing the Multiface (since thats
>> what I can test) and probably not polish it much, since
>> what I need is probably very basic.
>>
>> Oh, and BTW, during coding of hdsposc a question arose:
>> Is it recommended practice to immediately close a hwdep device
>> again after performing a single operation, or would it be OK
>> to leave the hwdep handle open during runtime and only close it
>> again on program shutdown?
>
> Hi Mario !
>
> This is great. Doing this has been part of my plan for the hdsp for a
> long time,

Great, I already kind of hoped you'd take the idea that way. All arguments
below aside, its the code duplication alone that really bugs me.

> but it's been delayed and delayed, and I have to admit that there is
> nearly no chance that I could find time to work on this in the next
> months.
>
> I'll explain here what I had in mind with the avowed hope to push you in
> this direction as I believe this is the way to go :)
>
> Situation :
> The hdsp is a great piece of hardware, and very straightforward to
> handle as almost everything is done in hardware. The alsa ctls the
> driver exports reflect this. But now comes the problem : if you ever
> used totalmix/hdspmixer, you probably used the last row (Output row).
> It is very useful, but here's how it works: every time you manipulate
> this row, hdspmixer/totalmix has to calculate and apply the attenuation
> coefficient to all streams routed to the specific physical output you
> targeted. Why is this a problem ? Because there is some information in
> hdspmixer that is not present in the hardware, and gets lost when
> hdspmixer is no more available.

I am not sure that I really understand. There is a hwdep ioctl to
receive the cuttent mixer matrix, wouldnt that kind of suffice to reconstruct
the gui? Or am I completely missing something else here? Mind my
situation, I have not use hdspmixer before, since I cant actually see its output.
So I have learned from the code, mostly.

> Also this prevents different application to access the mixer at the
> same time and share a common representation. If you play with
> amixer and the mixer ctl while hdspmixer is running, you'll
> invalidate hdspmixer's representation. And of course you can't use
> the very nice alsa monitoring/callback mechanism on ctls.
>
> So what can we do ?
> Implement a daemon to hold this representation and share it with other
> apps through OSC. Then rewrite the hdsp* tools to optionally use the osc
> backend instead of talking directly to the card using ctls.

I'd prefer if the GUI frontends would be made frontends only, to eliminate
the duplicated code. But thats already very futuristic... :)

> What are the benefits and possibilities ?
> * can you imagine controlling a farm of hdsp powered machine with
> hdspmixer and hdspconf running on a (possibly) hdsp-less machine on the
> network ?
Sure :-)
> * have a pd or sc patch, or a ladspa plugin (automated in ardour ? :)
> control the card's mixer and visualise the changes with hdspmixer (or
> the opposite)
hdsposc already contains a prototype of a HDSP class for SC :-)
It doesnt do much more than measuring latency with a ping right now, but hey :-)
> * implement a ramping mechanism in the daemon to eliminate zipper noises
> when accessing the mixer, thus making the hw mixer usable in live
> conditions.
Hmm, lagtime, neat idea.
> * provide fake standard mixer ctls in the driver, like a "master volume"
> ctl for example. The ctl does nothing in kernel space, but the daemon
> has a callback registered on it and does the actual job when for example
> the gnome mixer applet requests a change. (and again all this can be
> visualised in hdspmixer).
That definitely goes over my capabilities regarding alsa hackage...
>
> I hope all this was more exciting than confusing,
> Thomas

I guess for now, I'll keep it simple, maybe someone can later take it
and work on from there to complete the whole task. My problem is basically
that I cant see the current GUIs, and it sounds like very hard work to
work out the complete underlying model from just reading (C++, eeeek!)
code.

-- 
CYa,
  Mario