// Programmer: Craig Stuart Sapp <craig@ccrma.stanford.edu>

//
// Programmer: Craig Stuart Sapp <[email protected]>
// Creation Date: Wed Jan 6 19:00:08 PST 1999
// Last Modified: Wed Jan 6 19:00:18 PST 1999
// Filename: insimple.c
// Syntax: C
// $Smake: gcc -O3 -Wall -o %b %f && strip %b
//
// Description: echos MIDI input to MIDI output with a transposition
// of the MIDI notes. This program was designed using
// an 88-key synthesizer (a Yamaha Disklavier), so it
// won't work the same with smaller-sized keyboards.
// The MIDI data is echoed back to the same device from
// which it originates, but you could modify the code
// to have the input sent to an alternate device
// output. You could also modify this program to
// produce chords when a single note is played on the
// keyboard.
//
// There are 13 control keys (or so) at the bottom of
// the keyboard. When you press the lowest note on the
// keyboard (A0), the transposition value will remain
// the same, but the transposition direction will
// switch -- from either up to down or down to up.
// The other low keys on the keyboard are used for
// specifying the transposition interval. B-flat0
// would set the transposition to a minor second (one
// semi-tone), B0 would be a major second, C1 is a
// minor third, and so on.
//

#include <sys/soundcard.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

#define MIDI_DEVICE "/dev/sequencer"

int main(int argc, char** argv) {
unsigned char packet[4];
int transposition = 7; // Tranposition of MIDI notes
int keyflag = 0; // true when next byte is a MIDI key number
int count = 0; // for checking on running status
int seqfd = -1; // sequencer file descriptor

if (argc == 2) {
transposition = atoi(argv[1]);
}

// first open the sequencer device for reading.
seqfd = open(MIDI_DEVICE, O_RDWR);
if (seqfd == -1) {
printf("Error: cannot open %s\n", MIDI_DEVICE);
exit(1);
}

// now just wait around for MIDI bytes to arrive, when they
// do, then send notes back out with a transposition
while (1) {
read(seqfd, &packet, sizeof(packet));

// process the device packet if it contains one MIDI Byte
if (packet[0] == SEQ_MIDIPUTC) {
printf("received MIDI byte: %d\n", packet[1]);
if ((packet[1] & 0xf0) == 0x80 || (packet[1] & 0xf0) == 0x90) {
keyflag = 1;
count = 0;
write(seqfd, &packet, sizeof(packet));
} else if (packet[1] > 0x7f) {
keyflag = 0;
write(seqfd, &packet, sizeof(packet));
} else if (keyflag) {
count++;
if (count % 2 == 1) {
if (packet[1] == 21) {
transposition = -transposition;
} else if (packet[1] <= 34) {
if (transposition < 0) {
transposition = - (packet[1] - 21);
} else {
transposition = packet[1] - 21;
}
}
packet[1] += transposition;
packet[1] = packet[1] % 0x80;
}
write(seqfd, &packet, sizeof(packet));
}
}
}

return 0;
}