Module expanders tutorial?

stoermelder · August 4, 2019, 6:09pm

Thanks, I had the same thoughts about expanders and this is really helpful!
Just one question: where is the instance of MessageBus defined? Is it a global variable?

jerrysv · August 4, 2019, 6:22pm

yes:

github.com

SVModular/CharredDesert/blob/v1.0/src/CharredDesert.hpp#L8-L12


      
            float values[8];
          };
          
          
          ////////////////////

in this case, it’s defined at plugin instantiation - hence my comment about adding message tagging. you’ll note that thee message bus in this case is using an array of floats.

marc_boule · August 4, 2019, 8:26pm

Thanks for sharing this Jerry, very interesting!

marcelo.f.dantas · November 16, 2019, 1:12pm

I have been thinking about the idea of a modular mixer, where each module (channel strip) is expander to its left one and mother to its right one … so to get a 4 channel mixer all you need to do is put 4 channel strips side by side, with probably a master to their right. Then you build your mixer whatever size you want. Though I have absolutely NO idea how to make an expander/mother (yet), this is what my ultimate goal would be. Do you guys, with more expander experience, see any problem with this? Feasible?

Vortico · November 16, 2019, 1:29pm

Should work. Has it not been done before?

stoermelder · November 16, 2019, 1:34pm

@Squinky has a mixer module „Form“ and expanders ExFor and ExTwo.

marcelo.f.dantas · November 16, 2019, 7:01pm

I will check it out, thank you.

Squinky · November 17, 2019, 2:33am

Yes, our modular mixers are very similar to what you are asking for. And they are open source so if you want to make you own you may find some info there. That said it was very difficult for us to get this to work, especially the rather trivial details around getting solo to work across the modules. don’t know if it’s cause or effect, but we have to confess our source code for the expander part of it is not super clear.

marcelo.f.dantas · January 15, 2020, 6:49pm

Just to be 100% sure … there should be nothing preventing a module to have expanders connected both to its left side and to its right side, right?

Vortico · January 15, 2020, 6:54pm

Correct.

Squinky · January 16, 2020, 5:13am

we put out mixer ex panders on the left, but that’s just because “real” mixers tend to be organized that way.

clone45 · May 17, 2022, 3:11pm

I’m revisiting this thread because my bi-directional expander code isn’t working. It’s easy to get confused with this stuff and I could use an example to follow. However, the link is broken to Andrew’s compact example. Does anyone know if it’s still around somewhere?

marc_boule · May 17, 2022, 7:28pm

The github issues were removed in that repo, so unless someone has a copy, it might be best to look at some code of an open source module that uses expanders. I have a few (as do many others), and I’m definitely not claiming to have the most elegant code, but perhaps some of my simpler modules like Clocked or ChordKey could be worth a look. In those cases, the buffers are declared as float arrays, but it can in fact be a struct to make management easier. I’ve done the struct method in MixMaster/AuxSpander, but that’s way more code to sift through perhaps than what is needed.

clone45 · May 18, 2022, 2:15am

Drat, I’m having trouble. Maybe I can talk it out here.

My main module (GrooveBox) expects the expansion module (GrooveBoxExpander) to be on the left-hand side.

I’m using two different structs for passing around the data: One for the expander → groovebox communication, and a different struct for the groovebox → expander communications…

I’ve been successful in sending data from the expander module to the groovebox module.

Here’s the structure used for sending information from the expander to the groovebox:

#pragma once

struct GrooveBoxExpanderMessage
{
  bool message_received = true;
  bool mutes[8];
  bool solos[8];
  float track_volumes[8];

  GrooveBoxExpanderMessage()
  {
    for(unsigned int i=0; i<8; i++)
    {
      mutes[i] = false;
      solos[i] = false;
      track_volumes[i] = 1.0;
    }
  }
};

In the Groovebox module, I define the following class variables:

  GrooveBoxExpanderMessage *producer_message = new GrooveBoxExpanderMessage;
  GrooveBoxExpanderMessage *consumer_message = new GrooveBoxExpanderMessage;

I’ve created a function that sends data from the Groovebox module to the expander which is called every frame:

  void processExpander()
  {
    if (leftExpander.module && leftExpander.module->model == modelGrooveBoxExpander)
    {
      // Receive message from expander
      GrooveBoxExpanderMessage *expander_message = (GrooveBoxExpanderMessage *) leftExpander.producerMessage;

      // Retrieve the data from the expander
      if(expander_message && expander_message->message_received == false)
      {
        // Copy the information in the structure to local variables.
        // This code was left out because it doesn't really pertain to
        // my question, and it's working fine.
        //
        // But saying that, here's just a taste:
        for(unsigned int i=0; i < NUMBER_OF_TRACKS; i++)
        {
           bool expander_mute_value = expander_message->mutes[i];
           // (I then store expander_mute_value locally)
        }

        // Set the received flag so we don't process the message every single frame
        expander_message->message_received = true;
      }

      leftExpander.messageFlipRequested = true;
    }
  }

So far, so good. That seems to work perfectly. However, now I wish to do the opposite: Send information from the groovebox module to the expander. First step, I created a struct to hold the data:

#pragma once

struct GrooveBoxMessage
{
  bool track_triggers[8];
  bool message_received = true;
  
  GrooveBoxMessage()
  {
    for(unsigned int i=0; i<8; i++)
    {
      track_triggers[i] = false;
    }
  }
};

And here’s my code in the GrooveBox that’s not working, with a clue to why:

It probably has something to do with this line:

GrooveBoxMessage *groovebox_message = (GrooveBoxMessage *) leftExpander.module->rightExpander.producerMessage;

And because I’m a bit confused about what’s going on. Thanks for any help you can muster!

carbon14 · May 18, 2022, 5:48am

I think it would be easier to combine the structures. Rely on one of the modules, either the parent, or the expander; to own those structures and coordinate the swap.

To keep things as clear as they are now; enclose one of each of your structures into a new structure.

carbon14 · May 18, 2022, 5:58am

I cant see anything in your code to set message received to false. But that is what you are testing for.

carbon14 · May 18, 2022, 6:09am

Also i notice that you have dynamically allocated your message structures. Are you disposing of them correctly? (Not related to your current issue)

You can avoid the dynamic allocation but using a static array of two structures.

marc_boule · May 18, 2022, 11:06am

Perhaps I’m understanding the code wrong and my comment will be besides the mark, but I think for a given direction of communication you always have to declare an array of 2 elements of the buffer you wish to use. For example, if I want to share 6 floats in one direction, it has to be declared as a double buffer:

github.com

MarcBoule/ImpromptuModular/blob/master/src/ChordKeyExpander.cpp#L35

      
        
            		NUM_OUTPUTS
            	};
            	enum LightIds {
            		NUM_LIGHTS
            	};
            
            
	// Constants
            	const float unusedValue = -100.0f;
            
            
	// Expander
            	float leftMessages[2][6] = {};// messages from mother (CvPad or ChordKey): 4 CV values, panelTheme, panelContrast
            
            
	// Need to save, no reset
            	// none
            	
            	// Need to save, with reset
            	// none
            	
            	// No need to save, with reset
            	float chordValues[4];
            	bool enabledNotes[12];

And when using a struct, it looks like this:

github.com

MarcBoule/MindMeldModular/blob/master/src/MixMaster/MixMaster.cpp#L75

      
        
            		NUM_LIGHTS
            	};
            
            
	typedef TAfmExpInterface<N_TRK, N_GRP> AfmExpInterface;
            
            

            
	#include "MixMaster.hpp"
            	
            	
            	// Expander
            	MfaExpInterface rightMessages[2];// messages from aux-expander, see MixerCommon.hpp
            
            
	// Constants
            	int numChannels16 = 16;// avoids warning that happens when hardcode 16 (static const or directly use 16 in code below)
            
            
	// Need to save, no reset
            	// none
            	
            	// Need to save, with reset
            	alignas(4) char trackLabels[4 * (N_TRK + N_GRP) + 4];// 4 chars per label, 16 (8) tracks and 4 (2) groups means 20 (10) labels, null terminate the end the whole array only, pad with three extra chars for alignment
            	GlobalInfo gInfo;

The whole mechanism has to be diligently followed, and for each direction the double buffer is really needed.

CountModula · May 18, 2022, 11:30am

You are trying to do 2 way communication between a module and an expander; am I understanding that right?

clone45 · May 18, 2022, 3:28pm

Yes, correct!