refactored code slightly

src/main.c

@@ -8,7 +8,7 @@
 #include <pthread.h>
 #include <stdatomic.h>
 
-static const char* devices[] = {"/dev/midi", "/dev/midi2", NULL};
+#include "midi_interface.h"
 
 typedef struct Note
 {
@@ -20,7 +20,7 @@ typedef struct Note
 typedef struct Offset
 {
     signed char pitch;
-    signed char velocity
+    signed char velocity;
 } Offset;
 
 static const Offset pattern[] = {
@@ -58,80 +58,78 @@ void *arpeggio_loop(void* data);
 
 int main(int argc, char** argv)
 {
-    unsigned char data[3] = {0, 0, 0};
+    MidiInterface interface;
+    int result = open_midi_device(&interface, NULL);
+    if(result < 0)
+        exit(result);
+
     int key_down = 0;
     Note current_note;
 
-    const char* device;
-    int fd;
-    int i = 0;
-    while((device = devices[i++]) != NULL)
-    {
-        printf("Trying %s...", device);
-
-        fd = open(device, O_RDWR, 0);
-        if(fd < 0)
-        {
-            printf("Failed: %s\n", strerror(errno));
-        }
-        else
-        {
-            printf("Success!\n");
-            break;
-        }
-    }
-
-    if(fd < 0)
-    {
-        fprintf(stderr, "No MIDI devices detected.\n");
-        return -1;
-    }
-
-    printf("Using MIDI device %s\n", device);
     pthread_t arpeggio_thread;
-    pthread_create(&arpeggio_thread, NULL, arpeggio_loop, (void*)fd);
+    pthread_create(&arpeggio_thread, NULL, arpeggio_loop, (void*)&interface);
+
+    Message* message;
+    create_message(&message);
 
     for(;;)
     {
-        read(fd, (void*)data, sizeof(data));
-
-        if(data[0] != 0xfd)
+        result = read_midi_device(interface, message);
+        if(result < 0)
         {
-            if(data[2] > 0)
+            fprintf(stderr, "Failed to read message: %s\n", midi_strerror(result));
+            if(result == MIDI_UNKNOWN_STATUS_BYTE)
             {
-                key_down = 1;
-                note = &current_note;
+                fprintf(stderr, "%x\n", message->type);
+                exit(result);
+            }
+        }
 
-                current_note.channel = 0x90;
-                current_note.pitch = data[1];
-                current_note.velocity = data[2];
-            }
-            else if(data[1] == current_note.pitch)
-            {
-                key_down = 0;
-                note = NULL;
-                step = 0;
-            }
+        // if(message->type != SYSTEM_EXCLUSIVE)
+            // printf("ch: %x, s: %x -- %02x %02x\n", message->channel, message->type, message->data[0], message->data[1]);
+
+        if(message->type == NOTE_ON)
+        {
+            key_down = 1;
+            note = &current_note;
+
+            current_note.channel = 0x90;
+            current_note.pitch = message->data[0];
+            current_note.velocity = message->data[1];
+        }
+        else if(message->type == NOTE_OFF && message->data[0] == note->pitch)
+        {
+            key_down = 0;
+            note = NULL;
+            step = 0;
         }
     }
 
     pthread_join(arpeggio_thread, NULL);
-    close(fd);
+    free_message(message);
+    close(interface.fd);
     return 0;
 }
 
 void *arpeggio_loop(void* data)
 {
-    int fd = (int)data;
+    MidiInterface* interface = (MidiInterface*)data;
+    Message* message;
+    create_message(&message);
+    message->channel = 0;
+    message->length = 2;
+    message->type = NOTE_ON;
 
     while(stop == 0)
     {
         if(note != NULL)
         {
             Note out = *note;
-            out.pitch += pattern[step].pitch;
-            out.velocity += pattern[step].velocity;
-            write(fd, &out, sizeof(Note));
+            message->data[0] = out.pitch + pattern[step].pitch;
+            message->data[1] = out.velocity + pattern[step].velocity;
+            int result = write_midi_device(*interface, message);
+            if(result < 0)
+                fprintf(stderr, "Failed to send message: %s\n", midi_strerror(result));
 
             step++;
             if(step >= (sizeof(pattern) / sizeof(Offset)))
@@ -140,4 +138,6 @@ void *arpeggio_loop(void* data)
             usleep(166666);
         }
     }
+
+    free_message(message);
 }

src/message.c

@@ -0,0 +1,81 @@
+#include "message.h"
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "midi_error.h"
+
+void create_message(Message** message)
+{
+    *message = (Message*)malloc(sizeof(Message));
+    (*message)->data = (uint8_t*)malloc(8);
+}
+
+void free_message(Message* message)
+{
+    free(message->data);
+    free(message);
+}
+
+int data_length(MessageType type)
+{
+    switch(type)
+    {
+    case NOTE_ON:   return 2;
+    case NOTE_OFF:  return 2;
+
+    case SYSTEM_EXCLUSIVE: return 0;
+    }
+
+    return MIDI_UNKNOWN_STATUS_BYTE;
+}
+
+int decode_status_byte(Message* message, uint8_t status)
+{
+    message->channel = (status & 0xF);
+    message->type = (status & 0xF0);
+    switch(status & 0xF0)
+    {
+    case 0x90:
+        message->type = NOTE_ON;
+        break;
+
+    case 0x80:
+        message->type = NOTE_OFF;
+        break;
+
+    case 0xF0:
+        message->type = SYSTEM_EXCLUSIVE;
+        break;
+
+    default:
+        return MIDI_UNKNOWN_STATUS_BYTE;
+    }
+
+    return 0;
+}
+
+int encode_status_byte(const Message* message, uint8_t* status)
+{
+    *status = 0;
+    *status |= (message->channel & 0xF);
+
+    switch(message->type)
+    {
+    case NOTE_ON:
+        *status |= 0x90;
+        break;
+
+    case NOTE_OFF:
+        *status |= 0x80;
+        break;
+
+    case SYSTEM_EXCLUSIVE:
+        *status |= 0xF0;
+        break;
+
+    default:
+        return MIDI_UNKNOWN_STATUS_BYTE;
+    }
+
+    return 0;   
+}

src/message.h

@@ -0,0 +1,28 @@
+#ifndef _MESSAGE_H_
+#define _MESSAGE_H_
+
+#include <stdint.h>
+
+typedef enum MessageType
+{
+    NOTE_OFF, NOTE_ON,
+    SYSTEM_EXCLUSIVE
+} MessageType;
+
+typedef struct Message
+{
+    uint8_t channel;
+    MessageType type;
+
+    int length;
+    uint8_t* data;
+} Message;
+
+void create_message(Message** message);
+void free_message(Message* message);
+
+int data_length(MessageType type);
+int decode_status_byte(Message* message, uint8_t status);
+int encode_status_byte(const Message* message, uint8_t* status);
+
+#endif

src/midi_error.c

@@ -0,0 +1,15 @@
+#include "midi_error.h"
+
+#include <stddef.h>
+
+static const char* error_messages[] = {
+    NULL, NULL,
+    "Failed to read from MIDI device.",
+    "Failed to write to MIDI device.",
+    "Unknown MIDI status byte"
+};
+
+const char* midi_strerror(MidiError error)
+{
+    return error_messages[-error];
+}

src/midi_error.h

@@ -0,0 +1,13 @@
+#ifndef _MIDI_ERROR_H_
+#define _MIDI_ERROR_H_
+
+typedef enum MidiError
+{
+    MIDI_READ_ERROR = -2, 
+    MIDI_WRITE_ERROR = -3,
+    MIDI_UNKNOWN_STATUS_BYTE = -4
+} MidiError;
+
+const char* midi_strerror(MidiError error);
+
+#endif

src/midi_interface.c

@@ -0,0 +1,90 @@
+#include "midi_interface.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <memory.h>
+
+static const char* devices[] = {"/dev/midi", "/dev/midi2", NULL};
+
+int try_open_device(const char* device);
+
+int open_midi_device(MidiInterface* interface, const char* device)
+{
+    int fd;
+
+    if(device != NULL)
+    {
+        fd = try_open_device(device);
+    }
+    else 
+    {
+        int i = 0;
+        while((device = devices[i++]) != NULL)
+        {
+            fd = try_open_device(device);
+            if(fd >= 0)
+                break;
+        }
+    }
+
+    if(device == NULL)
+        fprintf(stderr, "Failed to locate MIDI device.\n");
+    else if(fd < 0)
+        fprintf(stderr, "Failed to open MIDI device %s\n", device);
+    else
+        printf("Using device %s\n", device);
+
+    interface->fd = fd;
+    return fd;
+}
+
+int read_midi_device(MidiInterface interface, Message* buffer)
+{
+    uint8_t status;
+    int result = read(interface.fd, &status, 1);
+    if(result < 0)
+        return MIDI_READ_ERROR;
+
+    result = decode_status_byte(buffer, status);
+    if(result < 0)
+        return result;
+    
+    buffer->length = data_length(buffer->type);
+    if(buffer->length < 0)
+        return buffer->length;
+
+    result = read(interface.fd, buffer->data, buffer->length);
+    if(result < 0)
+        return MIDI_READ_ERROR;
+
+    if(buffer->type == NOTE_ON && buffer->data[1] == 0)
+    {
+        buffer->type = NOTE_OFF;
+    }
+
+    return 0;
+}
+
+int write_midi_device(MidiInterface interface, const Message* buffer)
+{
+    uint8_t status;
+    int result = encode_status_byte(buffer, &status);
+    if(result < 0)
+        return result;
+
+    uint8_t* buffer_out = (uint8_t*)malloc(1 + buffer->length);
+    buffer_out[0] = status;
+    memcpy(buffer_out + 1, buffer->data, buffer->length);
+
+    result = write(interface.fd, buffer_out, 1 + buffer->length);
+    if(result < 0)
+        return MIDI_WRITE_ERROR;
+}
+
+int try_open_device(const char* device)
+{
+    int fd = open(device, O_RDWR, 0);
+
+    return fd;
+}

src/midi_interface.h

@@ -0,0 +1,20 @@
+#ifndef _MIDI_INTERFACE_H_
+#define _MIDI_INTERFACE_H_
+
+#include <stdint.h>
+
+#include "message.h"
+#include "midi_error.h"
+
+typedef struct MidiInterface
+{
+    int fd;
+} MidiInterface;
+
+int open_midi_device(MidiInterface* interface, const char* device);
+
+int read_midi_device(MidiInterface interface, Message* buffer);
+int write_midi_device(MidiInterface interface, const Message* buffer);
+
+
+#endif