[LAD] Invitation - Control Chain interface and communication protocol

[Gianfranco Ceccolini]

Hi LADs

This is an invitation for all those who are interested in the Control Chain system, the MOD approach to external hardware controllers.

The Control Chain interface was conceived with the LV2 control ports properties in mind. It tries to dis-abstract the LV2 Control structure in tangible (and material) form.

The first purpose of the Control Chain was to connect the MOD and its external peripherals. The MIDI system is very generalistic and we didn’t want to design a “MIDI Clone”. As the LV2 standard enables the developers to add important metadata to describe the Control Ports, the MOD platform makes use of all this info to offer a good user experience to the musicians.

A good example is the footswitch.  The Control Chain footswitch has built in its firmware different behaviours depending on port properties. It alternates the state of toggles controls, it can trigger an event, it can run the items of an enumeration list and it can also measure time and offer TapTempo for time based units.

All this is accomplished with the same physical actuation - the pressing of the button - but according to the control that has been addressed to it. The GUI decides which actuator it offers the user for each of the Controls. 

The physical interface of the Control Chain devices is an RS-485 full-duplex serial line running at 1Mbit/sec.  Currently up to eight devices can be daisy chained and by use of the RJ-45 cable we also power the devices ( 1 pair for input,1 for output and 1 for power supply).

After some development we came to the conclusion that such a protocol could be extended for virtual devices in the GUI as well and this would make the development of plugins interfaces much easier.  

The reason for sharing this with the Linux Audio community is to involve as much people as possible in electing the needed features for the plugins. 

At this current state, the Control Chain supports only Input ControlPorts. People have been asking about the Tuner and other plugins that have Control Outputs. 

So we’re opening up the discussion to set the requirements and possibilities that shall be implemented.  

The discussion is to happen on our mailing list:

http://portalmod.com/cgi-bin/mailman/listinfo/developers <http://portalmod.com/cgi-bin/mailman/listinfo/developers>

and at the #portalmod IRC channel @ freenode.

Hope to see you all there

Kind regards

Gianfranco
The MOD Team
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