Communication/Serial/render.cpp

Serial communication

This example demonstrates how to receive and transmit serial data from Bela. When a 'k' or 's' are received on the specified serial port, a kick or snare sound, respectively, are generated.

Serial data is received in a lower-priority thread (an AuxiliaryTask). From there, relevant data is passed to the audio thread via a Pipe. The AuxiliaryTask is also writing to the serial port.

The sound generator is very simple and "retro". IT is using a decaying noise burst for the snare sound and a decaying sine sweep for the kick

/*
 ____  _____ _        _
| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
#include <Bela.h>
#include <libraries/Pipe/Pipe.h>
#include <libraries/Serial/Serial.h>
#include <cmath>

Serial gSerial;
Pipe gPipe;
unsigned int gSnareDuration;
int gSnareTime = 0;
unsigned int gKickDuration;
int gKickTime = 0;
float gKickPhase = 0;

void serialIo(void* arg) {
        while(!Bela_stopRequested())
        {
                unsigned int maxLen = 128;
                char serialBuffer[maxLen];
                // read from the serial port with a timeout of 100ms
                int ret = gSerial.read(serialBuffer, maxLen, 100);
                if (ret > 0) {
                        printf("Received: %.*s\n", ret, serialBuffer);
                        for(int n = 0; n < ret; ++n)
                        {
                                // when some relevant data is received
                                // send a notification to the audio thread via
                                // the pipe
                                // and send a reply on the serial port
                                if('k' == serialBuffer[n])
                                {
                                        gPipe.writeNonRt('k');
                                        gSerial.write("kick!\n\r");
                                } else if('s' == serialBuffer[n])
                                {
                                        gPipe.writeNonRt('s');
                                        gSerial.write("snare!\n\r");
                                }
                        }
                }
        }
}

bool setup(BelaContext *context, void *userData) {
        gSerial.setup ("/dev/ttyUSB0", 19200);
        AuxiliaryTask serialCommsTask = Bela_createAuxiliaryTask(serialIo, 0, "serial-thread", NULL);
        Bela_scheduleAuxiliaryTask(serialCommsTask);

        gPipe.setup("serialpipe", 1024);
        gKickDuration = 0.2 * context->audioSampleRate;
        gSnareDuration = 0.2 * context->audioSampleRate;

        return true;
}

void render(BelaContext *context, void *userData) {
        char c;
        // check if the serial thread has received any message and sent a notification
        while(gPipe.readRt(c) > 0)
        {
                // if there is, trigger the start of the respective sound
                if('s' == c)
                        gSnareTime = gSnareDuration;
                if('k' == c)
                        gKickTime = gKickDuration;
        }
        for(unsigned int n = 0; n < context->audioFrames; ++n)
        {
                // synthesize the snare and kick
                float snareOut = 0;
                float kickOut = 0;
                if(gSnareTime)
                {
                        // just a burst of white noise with a decaying envelope
                        float noise = 2.f * (rand() / (float)RAND_MAX) - 1.f;
                        float env = gSnareTime / (float)gSnareDuration;
                        snareOut = 0.4f * noise * env;
                        --gSnareTime;
                }
                if(gKickTime)
                {
                        // a descending sinewave
                        float frequency = map(gKickTime, gKickDuration, 0, 150, 20);
                        float env = gKickTime / (float)gKickDuration;
                        gKickPhase += 2.f * (float)M_PI * frequency / context->audioSampleRate;
                        if(gKickPhase > M_PI)
                                gKickPhase -= 2.f * (float)M_PI;
                        kickOut = env * sinf(gKickPhase);
                        --gKickTime;
                }
                float out = snareOut + kickOut;
                for(unsigned int ch = 0; ch < context->audioOutChannels; ++ch)
                {
                        audioWrite(context, n, ch, out);
                }
        }
}

void cleanup(BelaContext *context, void *userData) {}