/* MIDI-controlled tone generator
 * by Paul Coccoli
 * compile with: gcc -Wall midi-tg.c -o midi-tg -lm
 */

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <math.h>
#include <string.h>
#include <unistd.h>
#include <linux/soundcard.h>

#define DEVICE "/dev/dsp"
#define TRUE 1
#define FALSE 0
#define BUF_SIZE 16
#define AMP_MAX 0x7fff
#define AMP_MIN 0x8000

/* midi stuff */
enum MidiMessageType {
  NOTE_ON = 0x90
};
extern float notes[];

/* Compute the nth sample of a sine wave of frequency fHz sampled at rHz */
float sine(float f, int n, int r);

/* Open the OSS device */
int open_audio_dev(const char* dev, int format, int channels, int rate);

int main(int argc,char *argv[])
{
  /* OSS stuff */
  int stereo = FALSE;
  int rate = 44100;
  float freq = 440.0;
  int devfd;

  /* DSP stuff */
  int i, j;
  short int sample;
  char buffer[BUF_SIZE];

  /* midi stuff */
  int midifd;
  unsigned char midibuf[128];
  ssize_t len, n;
  int channel, notenum, velocity;

  if ((midifd = open("/dev/midi00", O_RDONLY|O_NONBLOCK|O_SYNC)) < 0) {
    perror("open: /dev/midi00");
  }

  if ((devfd = open_audio_dev(DEVICE, AFMT_S16_LE, stereo, 44100)) == -1) {
    fprintf(stderr, "open_audio_dev failed\n");
    exit(1);
  }

  i = 0; /* number of bytes in buffer */
  j = 0; /* number of samples in current cycle */

  channel = 0;
  notenum = 0;
  velocity = 0;

  while (TRUE) {
    /* First check for a note event */
    if ((len = read(midifd, midibuf, 128)) > 0) {
      midibuf[len] = '\0';
      switch (midibuf[0] & 0xf0) {
      case NOTE_ON: {
        channel = (short)(buffer[0] & 0x0f);
        notenum = (short)(midibuf[1]);
        velocity = (short)(midibuf[2]);

        freq = notes[notenum];

        if (velocity > 0) {
          printf("NOTE ON:  %f\n", freq);
        }
        else
          printf("NOTE OFF: %f\n", freq);
        break;
      }
      default:
      }
    }

    /* Compute next sample */
    sample = sine(freq, j, rate)*velocity/128*AMP_MAX;

    /* Put sample into buffer */
    buffer[i] = sample & 0xff;
    buffer[i+1] = (sample >> 8) & 0xff;
    i += 2;

    if (i >= BUF_SIZE) { /* Buffer is full */
      if ((n = write(devfd, buffer, i)) == -1) {
        perror("write");
        exit(1);
      }
      i = 0;
    }

    if (++j == rate) {
      j = 0;
    }

  }

  return 0;
}

/* Compute the nth sample of a sine wave of frequency fHz sampled at rHz */
float sine(float f, int n, int r) {
  float sample_num = ((int)f*n)%r;
  float x = sample_num/r;

  return sin(x*M_2_PI);
}

int open_audio_dev(const char* dev, int format, int channels, int rate) {
  int fd = -1;
  int orig_format = format;
  int orig_rate = rate;

  if ((fd = open(dev, O_WRONLY)) < 0) {
    perror("open");
    return fd;
  }

  if (ioctl(fd, SNDCTL_DSP_SETFMT, &format) == -1) {
    perror("ioctl");
    return -1;
  }
  if (format != orig_format) {
    fprintf(stderr, "SNDCTL_DSP_SETFMT failed\n");
    return -1;
  }

  if (ioctl(fd, SNDCTL_DSP_CHANNELS, &channels) == -1) {
    perror("ioctl");
    return -1;
  }
  if (channels != 1) {
    fprintf(stderr, "SNDCTL_DSP_CHANNELS failed\n");
    return -1;
  }

  if (ioctl(fd, SNDCTL_DSP_SPEED, &rate) == -1) {
    perror("ioctl");
    return -1;
  }
  if (rate != orig_rate) {
    fprintf(stderr, "SNDCTL_DSP_SPEED failed\n");
    return -1;
  }

  return fd;
}

/* MIDI note frequencies in Hz */
float notes[] =
{
    8.176,
    8.662,
    9.177,
    9.723,
    10.301,
    10.913,
    11.562,
    12.250,
    12.978,
    13.750,
    14.568,
    15.434,
    16.352,
    17.324,
    18.354,
    19.445,
    20.602,
    21.827,
    23.125,
    24.500,
    25.957,
    27.500,
    29.135,
    30.868,
    32.703,
    34.648,
    36.708,
    38.891,
    41.203,
    43.654,
    46.249,
    48.999,
    51.913,
    55.000,
    58.270,
    61.735,
    65.406,
    69.296,
    73.416,
    77.782,
    82.407,
    87.307,
    92.499,
    97.999,
    103.826,
    110.000,
    116.541,
    123.471,
    130.813,
    138.591,
    146.832,
    155.563,
    164.814,
    174.614,
    184.997,
    195.998,
    207.652,
    220.000,
    233.082,
    246.942,
    261.626,
    277.183,
    293.665,
    311.127,
    329.628,
    349.228,
    369.994,
    391.995,
    415.305,
    440.000,
    466.164,
    493.883,
    523.251,
    554.365,
    587.330,
    622.254,
    659.255,
    698.456,
    739.989,
    783.991,
    830.609,
    880.000,
    932.328,
    987.767,
    1046.502,
    1108.731,
    1174.659,
    1244.508,
    1318.510,
    1396.913,
    1479.978,
    1567.982,
    1661.219,
    1760.000,
    1864.655,
    1975.533,
    2093.005,
    2217.461,
    2349.318,
    2489.016,
    2637.020,
    2793.826,
    2959.955,
    3135.963,
    3322.438,
    3520.000,
    3729.310,
    3951.066,
    4186.009,
    4434.922,
    4698.636,
    4978.032,
    5274.041,
    5587.652,
    5919.911,
    6271.927,
    6644.875,
    7040.000,
    7458.620,
    7902.133,
    8372.018,
    8869.844,
    9397.273,
    9956.063,
    10548.08,
    11175.30,
    11839.82,
    12543.85
};