Stereo - Strange error compilation depending if a function was define before updateAudio() - Problem with preprocessor ?

Start with the minimal sketch in the issue and compare compilation with callback_updateEncodeurRotatif() before and after updateAudio(). Inspect mozzi_config.h and the AudioOutput.h include path, then verify that stereo compilation succeeds regardless of the callback's position while the mono case remains working.

Hello,

I got a really strange problem using the stereo mode on a pico using pt_8211 as output (I did not test on other platforms).

The problem

My code is using a rotary encoder and mozzi and looks like that (minimal code example, I remove a max of things) :

//********************************************************************
// 2023 Djevahirdjian Léo
//
// Bug Stereo - Minimal Code
//
//********************************************************************

//********************************************************************
//     DEFINITIONS - Interface
//********************************************************************
// Rotary encoder
# define ROT_PIN0 6
# define ROT_PIN1 7
#include <RotaryEncoder.h>
RotaryEncoder *interface_encodeurRotatif = nullptr ;

//  Definition of the function called when rottary encoder is used.
// THIS MAKE THE COMPILATION FAILS
void callback_updateEncodeurRotatif(){
  interface_encodeurRotatif->tick() ;
}

//********************************************************************
//     DEFINITIONS - Mozzi
//********************************************************************
#include <MozziGuts.h>
#include <AudioOutput.h>
// Template oscillateur
#include <Oscil.h>
// Chargement des tables pour oscillateurs
#include <tables/saw2048_int8.h>
#include <tables/sin2048_int8.h>

Oscil <SAW2048_NUM_CELLS, AUDIO_RATE> Oscillateur_Scie1(SAW2048_DATA) ;
Oscil <SAW2048_NUM_CELLS, AUDIO_RATE> Oscillateur_Scie2(SAW2048_DATA) ;

int CH1_frequence = 440 ;
int CH2_frequence = 220 ;

void updateControl() {
  Oscillateur_Scie1.setFreq(CH1_frequence) ;
  Oscillateur_Scie2.setFreq(CH2_frequence) ;
}

// Fonction de génération de la sortie
AudioOutput_t updateAudio() {
  return StereoOutput::fromNBit(9, Oscillateur_Scie1.next(), Oscillateur_Scie2.next()) ;
}


//********************************************************************
//     COEUR n°0 - Mozzi
//********************************************************************
void setup() {
}

void loop() {
}

//********************************************************************
//     COEUR n°1 - Interface
//********************************************************************
void setup1(void) {
}

void loop1(){
}

These return an error "Compilation error: 'StereoOutput' does not name a type".

Try 1 - Switch to Mono

Switching to Mono mode in mozzi_config.h, and replacing

return StereoOutput::fromNBit(9, Oscillateur_Scie1.next(), Oscillateur_Scie2.next()) ;
```c++

to

```c++
return MonoOutput::fromNBit(9, Oscillateur_Scie1.next()) ;

-> the compilation work. The problem seems linked to the stereo mode.

Try 2 - Find the disturbing element

I was able to find what make a mess but I don't uderstant why ^^. Moving the function definition of callback_updateEncodeurRotatif() after updateAudio and the sketch is compiled witout error :

//********************************************************************
// 2023 Djevahirdjian Léo
//
// Bug Stereo - Minimal Code
//
//********************************************************************

//********************************************************************
//     DEFINITIONS - Interface
//********************************************************************
// Rotary encoder
# define ROT_PIN0 6
# define ROT_PIN1 7
#include <RotaryEncoder.h>
RotaryEncoder *interface_encodeurRotatif = nullptr ;

//********************************************************************
//     DEFINITIONS - Mozzi
//********************************************************************
#include <MozziGuts.h>
#include <AudioOutput.h>
// Template oscillateur
#include <Oscil.h>
// Chargement des tables pour oscillateurs
#include <tables/saw2048_int8.h>
#include <tables/sin2048_int8.h>

Oscil <SAW2048_NUM_CELLS, AUDIO_RATE> Oscillateur_Scie1(SAW2048_DATA) ;
Oscil <SAW2048_NUM_CELLS, AUDIO_RATE> Oscillateur_Scie2(SAW2048_DATA) ;

int CH1_frequence = 440 ;
int CH2_frequence = 220 ;

void updateControl() {
  Oscillateur_Scie1.setFreq(CH1_frequence) ;
  Oscillateur_Scie2.setFreq(CH2_frequence) ;
}

// Fonction de génération de la sortie
AudioOutput_t updateAudio() {
  return StereoOutput::fromNBit(9, Oscillateur_Scie1.next(), Oscillateur_Scie2.next()) ;
}

// AFTER -> MAKE THE COMPILE WORKS IN STEREO
void callback_updateEncodeurRotatif(){
  interface_encodeurRotatif->tick() ;
}


//********************************************************************
//     COEUR n°0 - Mozzi
//********************************************************************
void setup() {
}

void loop() {
}

//********************************************************************
//     COEUR n°1 - Interface
//********************************************************************
void setup1(void) {
}

void loop1(){
}

Conclusion

I don't have a clue what happen, it's really strange... I don't know if that is a clue that something wrong is happening with stereo mode... Hope that can help.

Thanks for your good work :-)

Leo