MIDI BLE Tutorial

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Contributors: MTaylor
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Full MIDI BLE Converter

Combining the MIDI BLE Starter program, DIN to BLE program, and BLE to DIN program, a full program is written that converts MIDI messages both ways. Without the shield, this can be put on an nRF52832 that is connected to another processor's UART to add MIDI BLE to an existing MIDI device, such as the Tsunami.

language:c
#include <MIDI.h>
#include "nrf52.h"
#include <BLEPeripheral.h>

#define BLUE_STAT_PIN     7   // LED on pin 7
#define RED_STAT_PIN     11   // LED on pin 11
#define GREEN_STAT_PIN   12   // LED on pin 12
#define BTN_PIN           6   // User button 

unsigned long msOffset = 0;
#define MAX_MS 0x01FFF //13 bits, 8192 dec

// create peripheral instance, see pinouts above
//const char * localName = "nRF52832 MIDI";
BLEPeripheral blePeripheral;
BLEService service("03B80E5A-EDE8-4B33-A751-6CE34EC4C700");
BLECharacteristic characteristic("7772E5DB-3868-4112-A1A9-F2669D106BF3", BLERead | BLEWriteWithoutResponse | BLENotify, 20 );
BLEDescriptor descriptor = BLEDescriptor("2902", 0);

MIDI_CREATE_INSTANCE(HardwareSerial, Serial, MIDI);

void setup() {
    delay(1000);

    //Setup diag leds
    pinMode(BLUE_STAT_PIN, OUTPUT);
    pinMode(RED_STAT_PIN, OUTPUT);
    pinMode(GREEN_STAT_PIN, OUTPUT);
    digitalWrite(BLUE_STAT_PIN, 1);
    digitalWrite(RED_STAT_PIN, 1);
    digitalWrite(GREEN_STAT_PIN, 1);

    //Setup nRF52832 user button
    pinMode(BTN_PIN, INPUT_PULLUP);

    setupBLE();

    // Initiate MIDI communications, listen to all channels
    MIDI.begin(MIDI_CHANNEL_OMNI);
    MIDI.turnThruOff();

    // The nRF52832 converts baud settings to the discrete standard rates.
    // Use the nrf52.h names to write a custom value, 0x7FFC80 after beginning midi
    NRF_UARTE_Type * myUart;
    myUart = (NRF_UARTE_Type *)NRF_UART0_BASE;
    myUart->BAUDRATE = 0x7FFC80;

    //Write data to the serial output pin to make sure the serial output is working.
    //Sometimes serial output only allows 1 byte out then hangs.  Resetting the
    //nRF52832 resolves the issue
    digitalWrite(RED_STAT_PIN, 0);
    MIDI.sendNoteOn(42, 66, 1);
    delay(500);
    MIDI.sendNoteOff(42, 66, 1); 
    digitalWrite(RED_STAT_PIN, 1);

}

void loop()
{
    BLECentral central = blePeripheral.central();
    if(digitalRead(BTN_PIN) == 0){
        digitalWrite(GREEN_STAT_PIN, 0);
        MIDI.sendNoteOff(0x45, 80, 1);
        delay(100);
        digitalWrite(GREEN_STAT_PIN, 1);
    }
    if (central) {
        //Prep the timestamp
        msOffset = millis();

        digitalWrite(BLUE_STAT_PIN, 0);
        // central connected to peripheral

        while (central.connected()) {
            digitalWrite(GREEN_STAT_PIN, 0);
            //If connected, send midi data by the button here
            if(digitalRead(BTN_PIN) == 0){
                digitalWrite(GREEN_STAT_PIN, 0);
                MIDI.sendNoteOn(0x45, 80, 1);
                delay(100);
                MIDI.sendNoteOff(0x45, 80, 1);
                digitalWrite(GREEN_STAT_PIN, 1);
            }
            //Check if data exists coming in from BLE
            if (characteristic.written()) {
                digitalWrite(RED_STAT_PIN, 0);
                processPacket();
                digitalWrite(RED_STAT_PIN, 1); 
            }
            //Check if data exists coming in from the serial port
            parseMIDIonDIN();
        }
    }
    //No longer connected.  Turn off the LEDs.
    digitalWrite(BLUE_STAT_PIN, 1);
    digitalWrite(GREEN_STAT_PIN, 1);
    //Delay to show off state for a bit
    delay(100);
}

//This function decodes the BLE characteristics and calls transmitMIDIonDIN
//if the packet contains sendable MIDI data.
void processPacket()
{
    //Receive the written packet and parse it out here.
    uint8_t * buffer = (uint8_t*)characteristic.value();
    uint8_t bufferSize = characteristic.valueLength();

    //Pointers used to search through payload.
    uint8_t lPtr = 0;
    uint8_t rPtr = 0;
    //lastStatus used to capture runningStatus 
    uint8_t lastStatus;
    //Decode first packet -- SHALL be "Full MIDI message"
    lPtr = 2; //Start at first MIDI status -- SHALL be "MIDI status"
    //While statement contains incrementing pointers and breaks when buffer size exceeded.
    while(1){
        lastStatus = buffer[lPtr];
        if( (buffer[lPtr] < 0x80) ){
            //Status message not present, bail
            return;
        }
        //Point to next non-data byte
        rPtr = lPtr;
        while( (buffer[rPtr + 1] < 0x80)&&(rPtr < (bufferSize - 1)) ){
            rPtr++;
        }
        //look at l and r pointers and decode by size.
        if( rPtr - lPtr < 1 ){
            //Time code or system
            transmitMIDIonDIN( lastStatus, 0, 0 );
        } else if( rPtr - lPtr < 2 ) {
            transmitMIDIonDIN( lastStatus, buffer[lPtr + 1], 0 );
        } else if( rPtr - lPtr < 3 ) {
            transmitMIDIonDIN( lastStatus, buffer[lPtr + 1], buffer[lPtr + 2] );
        } else {
            //Too much data
            //If not System Common or System Real-Time, send it as running status
            switch( buffer[lPtr] & 0xF0 )
            {
            case 0x80:
            case 0x90:
            case 0xA0:
            case 0xB0:
            case 0xE0:
                for(int i = lPtr; i < rPtr; i = i + 2){
                    transmitMIDIonDIN( lastStatus, buffer[i + 1], buffer[i + 2] );
                }
                break;
            case 0xC0:
            case 0xD0:
                for(int i = lPtr; i < rPtr; i = i + 1){
                    transmitMIDIonDIN( lastStatus, buffer[i + 1], 0 );
                }
                break;
            default:
                break;
            }
        }
        //Point to next status
        lPtr = rPtr + 2;
        if(lPtr >= bufferSize){
            //end of packet
            return;
        }
    }
}

//This function takes a midi packet as input and calls the appropriate library
//function to transmit the data.  It's a little redundant because the library
//reforms midi data from the calls and sends it out the serial port.
//
//Ideally, the MIDI BLE object would feed a MIDI library object as a serial
//object removing all of this code.
//
//A benefit of this redundant code is that it's easy to filter messages, and
//exposes how the library works.
void transmitMIDIonDIN( uint8_t status, uint8_t data1, uint8_t data2 )
{
    uint8_t channel = status & 0x0F;
    channel++;
    uint8_t command = (status & 0xF0) >> 4;
    switch(command)
    {
    case 0x08: //Note off
        MIDI.sendNoteOff(data1, data2, channel);
        break;
    case 0x09: //Note on
        MIDI.sendNoteOn(data1, data2, channel);
        break;
    case 0x0A: //Polyphonic Pressure
        MIDI.sendAfterTouch(data1, data2, channel);
        break;
    case 0x0B: //Control Change
        MIDI.sendControlChange(data1, data2, channel);
        break;
    case 0x0C: //Program Change
        MIDI.sendProgramChange(data1, channel);
        break;
    case 0x0D: //Channel Pressure
        MIDI.sendAfterTouch(data2, channel);
        break;
    case 0x0E: //Pitch Bend
        MIDI.send(midi::PitchBend, data1, data2, channel);
        break;
    case 0x0F: //System
        switch(status)
        {
            case 0xF1: //MTC Q frame
                MIDI.sendTimeCodeQuarterFrame( data1 );
                break;
            case 0xF2: //Song position
                MIDI.sendSongPosition(( (uint16_t)(data1 & 0x7F) << 7) | (data2 & 0x7F));
                break;
            case 0xF3: //Song select
                MIDI.sendSongSelect( data1 );
                break;
            case 0xF6: //Tune request
                MIDI.sendTuneRequest();
                break;
            case 0xF8: //Timing Clock
            case 0xFA: //Start
            case 0xFB: //Continue
            case 0xFC: //Stop
            case 0xFE: //Active Sensing
            case 0xFF: //Reset
                MIDI.sendRealTime( (midi::MidiType)status );
                break;
            default:
                break;
        }
        break;
    default:
        break;
    }   
}

//This function is called to check if MIDI data has come in through the serial port.  If found, it builds a characteristic buffer and sends it over BLE.
void parseMIDIonDIN()
{
    uint8_t msgBuf[5]; //Outgoing buffer

    //Calculate timestamp.
    unsigned long currentMillis = millis();
    if(currentMillis < 5000){
        if(msOffset > 5000){
            //it's been 49 days! millis rolled.
            while(msOffset > 5000){
                //roll msOffset - this should preserve current ~8 second count.
                msOffset += MAX_MS;
            }
        }
    }
    //if the offset is more than 2^13 ms away, move it up in 2^13 ms intervals
    while(currentMillis >= (unsigned long)(msOffset + MAX_MS)){
        msOffset += MAX_MS;
    }
    unsigned long currentTimeStamp = currentMillis - msOffset;
    msgBuf[0] = ((currentTimeStamp >> 7) & 0x3F) | 0x80; //6 bits plus MSB
    msgBuf[1] = (currentTimeStamp & 0x7F) | 0x80; //7 bits plus MSB

    //Check MIDI object for new data.
    if (  MIDI.read())
    {
        digitalWrite(RED_STAT_PIN, 0);
        uint8_t statusByte = ((uint8_t)MIDI.getType() | ((MIDI.getChannel() - 1) & 0x0f));
        switch (MIDI.getType())
        {
            //2 Byte Channel Messages
            case midi::NoteOff :
            case midi::NoteOn :
            case midi::AfterTouchPoly :
            case midi::ControlChange :
            case midi::PitchBend :
                msgBuf[2] = statusByte;
                msgBuf[3] = MIDI.getData1();
                msgBuf[4] = MIDI.getData2();
                characteristic.setValue(msgBuf, 5);
                break;
            //1 Byte Channel Messages
            case midi::ProgramChange :
            case midi::AfterTouchChannel :
                msgBuf[2] = statusByte;
                msgBuf[3] = MIDI.getData1();
                characteristic.setValue(msgBuf, 4);
                break;
            //System Common Messages
            case midi::TimeCodeQuarterFrame :
                msgBuf[2] = 0xF1;
                msgBuf[3] = MIDI.getData1();
                characteristic.setValue(msgBuf, 4);
                break;
            case midi::SongPosition :
                msgBuf[2] = 0xF2;
                msgBuf[3] = MIDI.getData1();
                msgBuf[4] = MIDI.getData2();
                characteristic.setValue(msgBuf, 5);
                break;
            case midi::SongSelect :
                msgBuf[2] = 0xF3;
                msgBuf[3] = MIDI.getData1();
                characteristic.setValue(msgBuf, 4);
                break;
            case midi::TuneRequest :
                msgBuf[2] = 0xF6;
                characteristic.setValue(msgBuf, 3);
                break;
                //Real-time Messages
            case midi::Clock :
                msgBuf[2] = 0xF8;
                characteristic.setValue(msgBuf, 3);
                break;
            case midi::Start :
                msgBuf[2] = 0xFA;
                characteristic.setValue(msgBuf, 3);
                break;
            case midi::Continue :
                msgBuf[2] = 0xFB;
                characteristic.setValue(msgBuf, 3);
                break;
            case midi::Stop :
                msgBuf[2] = 0xFC;
                characteristic.setValue(msgBuf, 3);
                break;
            case midi::ActiveSensing :
                msgBuf[2] = 0xFE;
                characteristic.setValue(msgBuf, 3);
                break;
            case midi::SystemReset :
                msgBuf[2] = 0xFF;
                characteristic.setValue(msgBuf, 3);
                break;
            //SysEx
            case midi::SystemExclusive :
//              {
//                  // Sysex is special.
//                  // could contain very long data...
//                  // the data bytes form the length of the message,
//                  // with data contained in array member
//                  uint16_t length;
//                  const uint8_t  * data_p;
//  
//                  Serial.print("SysEx, chan: ");
//                  Serial.print(MIDI.getChannel());
//                  length = MIDI.getSysExArrayLength();
//  
//                  Serial.print(" Data: 0x");
//                  data_p = MIDI.getSysExArray();
//                  for (uint16_t idx = 0; idx < length; idx++)
//                  {
//                      Serial.print(data_p[idx], HEX);
//                      Serial.print(" 0x");
//                  }
//                  Serial.println();
//              }
                break;
            case midi::InvalidType :
            default:
                break;
        }
        digitalWrite(RED_STAT_PIN, 1);
    }

}

void setupBLE()
{
    blePeripheral.setLocalName("nRF52832 MIDI"); //local name sometimes used by central
    blePeripheral.setDeviceName("nRF52832 MIDI"); //device name sometimes used by central
    //blePeripheral.setApperance(0x0000); //default is 0x0000, what should this be?
    blePeripheral.setAdvertisedServiceUuid(service.uuid()); //Advertise MIDI UUID

    // add attributes (services, characteristics, descriptors) to peripheral
    blePeripheral.addAttribute(service);
    blePeripheral.addAttribute(characteristic);
    blePeripheral.addAttribute(descriptor);

    // set initial value
    characteristic.setValue(0);

    blePeripheral.begin();
}