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JamesDunne/midi.c

Created February 20, 2017 16:29
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  1. JamesDunne created this gist Feb 20, 2017.
    119 changes: 119 additions & 0 deletions midi.c
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,119 @@
    #include <stdio.h>
    #include <stdarg.h>
    #include <string.h>

    #include <errno.h>
    #include <fcntl.h>
    #include <asm/termios.h>
    #include <unistd.h>

    typedef unsigned char u8;

    // Global variable for holding file descriptor to talk to UART0 for MIDI communications:
    int uart0_fd = -1;
    // Default UART0 device name on Raspberry Pi Model B:
    const char *midi_fname = "/dev/ttyAMA0";

    // Open UART0 device for MIDI communications and set baud rate to 31250 per MIDI standard:
    int midi_init(void) {
    struct termios2 tio;

    uart0_fd = open(midi_fname, O_RDWR | O_NOCTTY | O_NONBLOCK);
    if (uart0_fd == -1) {
    char err[100];
    sprintf(err, "open('%s')", midi_fname);
    perror(err);
    return -1;
    }

    // Requirements:
    // * UART0 is enabled
    // * UART0 is unused by the system for any ttys (remove mention of ttyAMA0 from `/etc/inittab`)
    // * UART0 clock rate is set to default of 3MHz in /boot/config.txt
    // * `init_uart_clock=3000000`
    // * UART0 clock rate for Linux is set to default of 3MHz in /boot/cmdline.txt
    // * `bcm2708.uart_clock=3000000`
    //
    // NOTE: Any hacks to change the default UART clock speed of the RPi B to adjust the
    // standard baud rates of 38400 to actually be ~31250 DO NOT WORK on latest Raspbian
    // kernels. I'm using `Linux 4.1.18 armv6l` as of 2017-02-20.
    //
    // The only thing that DOES work on latest Raspbian kernels is the code below which uses
    // termios2 to set a custom baud rate of 31250 which is the MIDI standard.

    // Set baud rate to 31250 for MIDI:
    ioctl(uart0_fd, TCGETS2, &tio);
    tio.c_cflag &= ~CBAUD;
    tio.c_cflag |= BOTHER;
    tio.c_ispeed = 31250;
    tio.c_ospeed = 31250;
    ioctl(uart0_fd, TCSETS2, &tio);

    return uart0_fd;
    }

    void midi_send_cmd1_impl(u8 cmd_byte, u8 data1) {
    int count;
    u8 buf[2];
    buf[0] = cmd_byte;
    buf[1] = data1;
    count = write(uart0_fd, buf, 2);
    if (count != 2) {
    perror("Error sending MIDI bytes");
    return;
    }
    printf("MIDI: %02X %02X\n", cmd_byte, data1);
    }

    void midi_send_cmd2_impl(u8 cmd_byte, u8 data1, u8 data2) {
    int count;
    u8 buf[3];
    buf[0] = cmd_byte;
    buf[1] = data1;
    buf[2] = data2;
    count = write(uart0_fd, buf, 3);
    if (count != 3) {
    perror("Error sending MIDI bytes");
    return;
    }
    printf("MIDI: %02X %02X %02X\n", cmd_byte, data1, data2);
    }

    // 256 byte buffer for batching up SysEx data to send in one write() call:
    u8 sysex[256];
    size_t sysex_p = 0;

    // Buffer up SysEx data until terminating F7 byte is encountered:
    void midi_send_sysex(u8 byte) {
    //printf("MIDI: %02X\n", byte);

    if (sysex_p >= 256) {
    fprintf(stderr, "MIDI SysEx data too large (>= 256 bytes)\n");
    return;
    }

    // Buffer data:
    sysex[sysex_p++] = byte;

    if (byte == 0xF7) {
    size_t i;
    size_t write_count = sysex_p;
    sysex_p = 0;

    printf("MIDI SysEx:");
    for (i = 0; i < write_count; i++) {
    printf(" %02X", sysex[i]);
    }
    printf("\n");

    ssize_t count = write(uart0_fd, sysex, write_count);
    if (count < 0) {
    perror("write in midi_send_sysex");
    return;
    }
    if (count != write_count) {
    fprintf(stderr, "midi_send_sysex write didnt write enough bytes\n");
    return;
    }
    }
    }