ALSA control service in user space

[Scott Bahling]

Hi Takashi,

On Fri, 2020-06-05 at 10:18 +0900, Takashi Sakamoto wrote:
> Hi Scott,
> 
> On Thu, Jun 04, 2020 at 09:02:23PM +0200, Scott Bahling wrote:
> > Hi Takashi,
> > 
> > On Wed, 2020-06-03 at 19:05 +0900, Takashi Sakamoto wrote:
> > > Now instead of Python 3, I select Rust language to write the server
> > > programs for audio and music units on IEEE 1394 bus. The hinawa-rs helps
> > > the third and fourth of the above tasks.
> > 
> > What does this mean for the future of hinawa-utils?
> 
> I'm sorry to puzzle you but I shift my effort of userspace applications
> from hinawa-utils into the services.
> 
> As you can see, Python 3 scripts in hinawa-utils depends on 'libhinawa 1'
> which produces 'Hinawa-2.0.gir'. On the other hand, libhinawa 2 produces
> 'Hinawa-3.0.gir'. Although hinawa-utils needs to be arranged for its
> dependency to the latest libhinawa, at present I have no plan for it due
> to the rest of my time... Therefore hinawa-utils is actually going to become
> abandoned now at least Python 3 areas, unfortunately.
> 
> > I have created an OSC server interface[1] to the Tascam FW-1884 control
> > surface using a fork of the hinawa-utils with a few enhancements[2]. The
> > OSC server works great for controlling applications like Ardour with the
> > FW-1884.
> 
> I'm interested in Open Sound Control protocol itself, and I would use it
> if I were a developer out of alsa-project. However it's secondary option
> to me if any ALSA interface assists me to achieve the aim.
> 
> Now I made the repository public[1] for your information. The 'topic/work'
> branch includes the latest codes for the services[2]. You can see many
> protocols are already added. (The most of them are just makeshift...)
> 
> For Tascam FireWire series, I uses two types of ALSA interfaces for
> inter-process communication between the service and ALSA applications:
> 
> - interface on ALSA control character device
> - interface on ALSA sequencer character device
> 
> For FW-1884, below elements are transparently visible for ALSA control
> applications (e.g. amixer, qashctl):
> 
>  * clock-source
>  * clock-rate
>  * input-threshold
>  * coax-output-source
>  * master-fader-assign
>  * host-mode
>  * opt-output-source
>  * spdif-input-source
>  * monitoring (to start polling for below elements)
>  * monitor-rotary (readonly)
>  * solo-rotary (readonly)
>  * input-meters (readonly)
>  * output-meters (readonly)
>  * detected-clock-source (readonly)
>  * detected-clock-rate (readonly)
>  * monitor-meters (readonly)
>  * analog-mixer-meters (readonly)
>  * monitor-mode (readonly)
> 
> Additionally, 'FW-1884' port is opened to ALSA Sequencer. The events generated
> by touching control surfaces such as fader, rotary are converted to standard
> MIDI messages and sent to the port. Any ALSA Sequencer application can receive
> the messages via the port. Ardour is such an application.

Very nice! I'm particularly interested in the monitoring controls which is
currently missing and would be useful.

> You can see the conversion in 'src/tascam/isoch/seq_ctl.rs'[3] and everything
> is hard-coded. It's possible to be more inconvenient than your implementation.
> 
> > I was just cleaning up the code and was prepared to submit my patches for
> > hinawa-utils, but if that will go unmaintained, I might just integrate the
> > hinawa-utils parts into my OSC server code and only depend on libhinawa
> > directly. What do you recommend?
> > 
> > [1] https://gitlab.com/tascam-fw-1884/tascam-fw-osc
> > [2] https://github.com/sbahling/hinawa-utils/compare/master...fw-1884
> 
> The integration into your repository is easy and convenient to you. I
> recommend it. But I'm welcome your comment and patches for the service itself
> when the service officially starts for public development.
> 
> 
> Well, from my interests, how do you implement to blight 'REC' LEDs? It's my
> concern when using ALSA Sequencer because MIDI standard has no
> specification to associate LED and messages.

With Ardour OSC the state of record enable/disable for each channel is sent
using the following message format:

command           channel  state 
/strip/recenable  1        1
/strip/recenable  1        0

I listen for those events and turn the LED on or off depending on the state
of channel it's assigned to.  For a MIDI implementation if there is not a
standard, I guess you need to just pick a note or control signal to use.
There seems to be no standard for many controls and different units have
their own MIDI mappings.

An example of mappings can be found in the Ardour code[ [1]. A description
of how map MIDI messages to Ardour actions is in the docs [2]. Unfortunately
,given no standard, each application needs to be configured/adjusted to use
any particular controller. Even with my OSC implementation I have API
translation service to translate the general FW-1884 API that I came up with
to specific applications like Ardour.

I looked into MIDI briefly at first, but an OSC implementation seemed easier
and more flexible to me. I think it's a better fit for complex control
surfaces. But it's not as ubiquitous as MIDI so a MIDI implementation would
be useful.

[1] https://github.com/Ardour/ardour/tree/master/share/midi_maps
[2] https://manual.ardour.org/using-control-surfaces/generic-midi/midi-binding-maps/

Scott
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