arduino
Comunicación MIDI

Introducción

Ejemplo de MIDI THRU

El MIDI Thru es simple y fácil de probar. Cuando trabaje correctamente, podrá instalar su proyecto Arduino entre dos dispositivos MIDI, MIDI IN a MIDI OUT y podrá verificar que los dos dispositivos funcionan juntos. Si tiene la capacidad de medir la latencia, verá un aumento debido a las instrucciones de captura y retransmisión del búfer en serie.

// This is a simple MIDI THRU.  Everything in, goes right out.
// This has been validate on an Arduino UNO and a Olimex MIDI Shield  

boolean byteReady; 
unsigned char midiByte;

void setup() {
    // put your setup code here, to run once:
    //  Set MIDI baud rate:
    Serial.begin(31250);
    byteReady = false;
    midiByte = 0;  
}

// The Loop that always gets called...
void loop() {
   if (byteReady) {
        byteReady = false;
        Serial.write(midiByte);
    }
}

// The little function that gets called each time loop is called.  
// This is automated somwhere in the Arduino code.
void serialEvent() {
  if (Serial.available()) {
    // get the new byte:
    midiByte = (unsigned char)Serial.read();
    byteReady = true;
  }
}

MIDI a través de la cola

// This is a more complex MIDI THRU.  This version uses a queue.  Queues are important because some
// MIDI messages can be interrupted for real time events.  If you are generating your own messages,
// you may need to stop your message to let a "real time" message through and then resume your message.


#define QUEUE_DEPTH 128

// Queue Logic for storing messages
int headQ = 0;
int tailQ = 0;
unsigned char tx_queue[QUEUE_DEPTH];

void setup() {
    // put your setup code here, to run once:
    //  Set MIDI baud rate:
    Serial.begin(31250);
}

// getQDepth checks for roll over.  Folks have told me this 
// is not required.  Feel free to experiment.
int getQDepth() {
int depth = 0;
    if (headQ < tailQ) {
        depth = QUEUE_DEPTH - (tailQ - headQ);
    } else {
        depth = headQ - tailQ;
    }
    return depth;
}

void addQueue (unsigned char myByte) {
    int depth = 0;
    depth = getQDepth();

    if (depth < (QUEUE_DEPTH-2)) {
        tx_queue[headQ] = myByte;
        headQ++;
        headQ = headQ % QUEUE_DEPTH; // Always keep the headQ limited between 0 and 127
    }
}

unsigned char deQueue() {
    unsigned char myByte;
    myByte = tx_queue[tailQ];
    tailQ++;
    tailQ = tailQ % QUEUE_DEPTH;  // Keep this tailQ contained within a limit
    // Now that we dequeed the byte, it must be sent. 
    return myByte;
}

void loop() {
   if (getQDepth>0) {
        Serial.write(deQueue());
    }
}

// The little function that gets called each time loop is called.  
// This is automated somwhere in the Arduino code.
void serialEvent() {
  if (Serial.available()) {
    // get the new byte:
    addQueue((unsigned char)Serial.read());;
  }
}

Generación de reloj MIDI

// This is a MiDI clk generator.  This takes a #defined BPM and 
// makes the appropriate clk rate.  The queue is used to let other messages 
// through, but allows a clock to go immediately to reduce clock jitter

#define QUEUE_DEPTH 128
#define BPM 121
#define MIDI_SYSRT_CLK 0xF8

// clock tracking and calculation
unsigned long lastClock;
unsigned long captClock;
unsigned long clk_period_us;

// Queue Logic for storing messages
int headQ = 0;
int tailQ = 0;
unsigned char tx_queue[QUEUE_DEPTH];

void setup() {
    //  Set MIDI baud rate:
    Serial.begin(31250);
    clk_period_us = 60000000 / (24 * BPM);
    lastClock = micros();
}

// getQDepth checks for roll over.  Folks have told me this 
// is not required.  Feel free to experiment.
int getQDepth() {
int depth = 0;
    if (headQ < tailQ) {
        depth = QUEUE_DEPTH - (tailQ - headQ);
    } else {
        depth = headQ - tailQ;
    }
    return depth;
}

void addQueue (unsigned char myByte) {
    int depth = 0;
    depth = getQDepth();

    if (depth < (QUEUE_DEPTH-2)) {
        tx_queue[headQ] = myByte;
        headQ++;
        headQ = headQ % QUEUE_DEPTH; // Always keep the headQ limited between 0 and 127
    }
}

unsigned char deQueue() {
    unsigned char myByte;
    myByte = tx_queue[tailQ];
    tailQ++;
    tailQ = tailQ % QUEUE_DEPTH;  // Keep this tailQ contained within a limit
    // Now that we dequeed the byte, it must be sent. 
    return myByte;
}

void loop() {
    captClock = micros();
    
    if (lastClock > captClock) {
        // we have a roll over condition - Again, maybe we don't need to do this.
        if (clk_period_us <= (4294967295 - (lastClock - captClock))) {
            // Add a the ideal clock period for this BPM to the last measurement value
            lastClock = lastClock + clk_period_us;
            // Send a clock, bypasing the transmit queue
            Serial.write(MIDI_SYSRT_CLK);
        }
    } else if (clk_period_us <= captClock-lastClock) {
        // Basically the same two commands above, but not within a roll over check
        lastClock = lastClock + clk_period_us;
        // Send a clock, bypasing the transmit queue
        Serial.write(MIDI_SYSRT_CLK);
    }

    if (getQDepth>0) {
        Serial.write(deQueue());
    }
}

// The little function that gets called each time loop is called.  
// This is automated somwhere in the Arduino code.
void serialEvent() {
  if (Serial.available()) {
    // get the new byte:
    addQueue((unsigned char)Serial.read());;
  }
}

Mensajes MIDI definidos

En general, el protocolo MIDI se divide en "mensajes". Hay 4 clases generales de mensajes:

• Canal de voz
• Modo de canal
• Sistema Común
• Mensajes en tiempo real del sistema

Los mensajes comienzan con un valor de byte por encima de 0x80. Cualquier valor por debajo de 0x7F se considera datos. Lo que significa efectivamente que 127 es el valor máximo que se puede codificar en un solo byte de datos MIDI. Para codificar valores más grandes, se requieren dos o más bytes de datos MIDI.

Debe señalarse que los mensajes deben enviarse de principio a fin sin interrupción ... EXCEPTO ... Los mensajes del sistema en tiempo real, que son un solo byte, que se pueden inyectar en medio de cualquier mensaje.

Mensajes de voz del canal

Mensajes de modo de canal

Mensajes comunes del sistema

Mensajes en tiempo real del sistema