src/command.h

@@ -0,0 +1,19 @@
+#ifndef COMMAND_H
+#define COMMAND_H
+
+typedef enum {
+    CMD_CYCLE,          // toggle record/stop for a channel
+    CMD_STOP,           // force to idle
+    // CMD_LOOP_TOGGLE not needed, CYCLE covers it
+    CMD_BIND_CHANNEL,   // bind a channel index (data = channel)
+    CMD_UNBIND,         // reset bind to channel 0
+    // ADD and REMOVE are still driven via atomics for now
+} cmd_type_t;
+
+typedef struct {
+    cmd_type_t type;
+    int        channel;   // which channel; -1 means "current/bound"
+    int        data;      // extra parameter (e.g. bind channel number)
+} command_t;
+
+#endif

src/looper.c

@@ -9,6 +9,8 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include "command.h"
+#include "queue.h"
 
 /* Global state (shared across files) */
 struct channel_t channels[MAX_CHANNELS];
@@ -20,10 +22,46 @@ jack_port_t *midi_control_port = NULL;
 jack_port_t *midi_clock_port = NULL;
 atomic_int control_key_active = 0;
 atomic_int bind_channel = 0;
+spsc_queue_t cmd_queue;
 
 /* Deferred removal index (1 second grace) */
 static int pending_unregister_idx = -1;
 
+static void apply_command(command_t cmd) {
+    switch (cmd.type) {
+    case CMD_CYCLE:
+        if (cmd.channel >= 0 && cmd.channel < MAX_CHANNELS) {
+            int cur = atomic_load(&channels[cmd.channel].state);
+            int next;
+            switch (cur) {
+            case STATE_IDLE:    next = STATE_RECORD;  break;
+            case STATE_RECORD:  next = STATE_LOOPING; break;
+            case STATE_LOOPING: next = STATE_PAUSED;  break;
+            case STATE_PAUSED:  next = STATE_LOOPING; break;
+            default:            next = STATE_IDLE;    break;
+            }
+            atomic_store(&channels[cmd.channel].state, next);
+        }
+        break;
+    case CMD_STOP:
+        if (cmd.channel >= 0 && cmd.channel < MAX_CHANNELS)
+            atomic_store(&channels[cmd.channel].state, STATE_IDLE);
+        else {
+            for (int i = 0; i < MAX_CHANNELS; i++)
+                atomic_store(&channels[i].state, STATE_IDLE);
+        }
+        break;
+    case CMD_BIND_CHANNEL:
+        atomic_store(&bind_channel, cmd.data);
+        break;
+    case CMD_UNBIND:
+        atomic_store(&bind_channel, 0);
+        break;
+    default:
+        break;
+    }
+}
+
 /* ----------------------------------------------------------------
  * process callback
  * ---------------------------------------------------------------- */
@@ -37,6 +75,12 @@ int process_callback(jack_nframes_t nframes, void *arg) {
     }
   }
 
+  /* drain RT‑safe commands */
+  command_t cmd;
+  while (queue_pop(&cmd_queue, &cmd)) {
+    apply_command(cmd);
+  }
+
   /* process each active channel */
   for (int c = 0; c < MAX_CHANNELS; c++) {
     if (!atomic_load(&channels[c].active))
@@ -171,6 +215,7 @@ void jack_shutdown_cb(void *arg) {
  * looper initialisation
  * ---------------------------------------------------------------- */
 int looper_init(jack_client_t *client) {
+  queue_init(&cmd_queue);
   /* channel 0 */
   channels[0].active = 1;
   atomic_store(&channels[0].state, STATE_IDLE);

src/main.c

@@ -1,5 +1,6 @@
 // cppcheck-suppress missingIncludeSystem
 #include "looper.h"
+#include "pipe.h"
 #include <jack/jack.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -33,6 +34,12 @@ int main(int argc, char *argv[]) {
     return 1;
   }
 
+  if (pipe_start_reader() != 0) {
+    fprintf(stderr, "pipe reader initialisation failed\n");
+    jack_client_close(client);
+    return 1;
+  }
+
   if (jack_activate(client)) {
     fprintf(stderr, "Cannot activate client\n");
     jack_client_close(client);

src/midi.c

@@ -1,6 +1,8 @@
 // cppcheck-suppress missingIncludeSystem
 #include "midi.h"
 #include "channel.h"
+#include "command.h"
+#include "queue.h"
 #include <jack/jack.h>
 #include <jack/midiport.h>
 #include <stdatomic.h>
@@ -9,6 +11,7 @@ extern atomic_int control_key_active;
 extern atomic_int cmd_add;
 extern atomic_int cmd_remove;
 extern atomic_int bind_channel;
+extern spsc_queue_t cmd_queue;
 
 void midi_handle_events(void *port_buffer, jack_nframes_t nframes) {
   (void)nframes;
@@ -34,7 +37,8 @@ void midi_handle_events(void *port_buffer, jack_nframes_t nframes) {
         if (ck) {
           atomic_store(&control_key_active, 0);
           if (note < 16) {
-            atomic_store(&bind_channel, note);
+            command_t cmd = { .type = CMD_BIND_CHANNEL, .channel = -1, .data = note };
+            queue_push(&cmd_queue, cmd);
           } else {
             switch (note) {
             case 60:
@@ -43,30 +47,19 @@ void midi_handle_events(void *port_buffer, jack_nframes_t nframes) {
             case 61:
               atomic_store(&cmd_remove, 1);
               break;
-            case 62: /* trigger looper – channel via bind_channel */
+            case 62:
             {
               int bch = atomic_load(&bind_channel);
               if (bch >= 0 && bch < MAX_CHANNELS) {
-                int cur = atomic_load(&channels[bch].state);
-                switch (cur) {
-                case STATE_IDLE:
-                  atomic_store(&channels[bch].state, STATE_RECORD);
-                  break;
-                case STATE_RECORD:
-                  atomic_store(&channels[bch].state, STATE_LOOPING);
-                  break;
-                case STATE_LOOPING:
-                  atomic_store(&channels[bch].state, STATE_PAUSED);
-                  break;
-                case STATE_PAUSED:
-                  atomic_store(&channels[bch].state, STATE_LOOPING);
-                  break;
-                }
+                command_t cmd = { .type = CMD_CYCLE, .channel = bch, .data = 0 };
+                queue_push(&cmd_queue, cmd);
               }
             } break;
-            case 63: /* unbind – reset bind to channel 0 */
-              atomic_store(&bind_channel, 0);
-              break;
+            case 63:
+            {
+              command_t cmd = { .type = CMD_UNBIND, .channel = -1, .data = 0 };
+              queue_push(&cmd_queue, cmd);
+            } break;
             default:
               break;
             }
@@ -74,23 +67,10 @@ void midi_handle_events(void *port_buffer, jack_nframes_t nframes) {
         } else {
           /* direct mapping */
           switch (note) {
-          case 1: /* toggle channel 0 */
+          case 1:
             {
-            int cur0 = atomic_load(&channels[0].state);
-            switch (cur0) {
-            case STATE_IDLE:
-              atomic_store(&channels[0].state, STATE_RECORD);
-              break;
-            case STATE_RECORD:
-              atomic_store(&channels[0].state, STATE_LOOPING);
-              break;
-            case STATE_LOOPING:
-              atomic_store(&channels[0].state, STATE_PAUSED);
-              break;
-            case STATE_PAUSED:
-              atomic_store(&channels[0].state, STATE_LOOPING);
-              break;
-            }
+              command_t cmd = { .type = CMD_CYCLE, .channel = 0, .data = 0 };
+              queue_push(&cmd_queue, cmd);
             } break;
           case 60:
             atomic_store(&cmd_add, 1);

src/pipe.c

@@ -0,0 +1,75 @@
+#include "pipe.h"
+#include "queue.h"
+#include "command.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+
+#define FIFO_PATH "/tmp/looper_cmd"
+#define LINE_MAX 256
+
+/* forward‑declare the global queue (defined in looper.c) */
+extern spsc_queue_t cmd_queue;
+
+/* external atomic flags for add/remove (defined in looper.c) */
+extern atomic_int cmd_add;
+extern atomic_int cmd_remove;
+
+static void *pipe_thread_func(void *arg) {
+    (void)arg;
+    FILE *fifo = fopen(FIFO_PATH, "r");
+    if (!fifo) {
+        perror("fopen fifo");
+        return NULL;
+    }
+    char line[LINE_MAX];
+    while (fgets(line, sizeof(line), fifo)) {
+        /* strip newline */
+        size_t len = strlen(line);
+        if (len > 0 && line[len-1] == '\n')
+            line[len-1] = '\0';
+
+        if (strcmp(line, "add") == 0) {
+            atomic_store(&cmd_add, 1);
+        } else if (strcmp(line, "remove") == 0) {
+            atomic_store(&cmd_remove, 1);
+        } else if (strncmp(line, "record ", 7) == 0) {
+            int ch = atoi(line + 7);
+            command_t cmd = { .type = CMD_CYCLE, .channel = ch, .data = 0 };
+            queue_push(&cmd_queue, cmd);
+        } else if (strcmp(line, "stop") == 0) {
+            command_t cmd = { .type = CMD_STOP, .channel = -1, .data = 0 };
+            queue_push(&cmd_queue, cmd);
+        } else if (strncmp(line, "bind ", 5) == 0) {
+            int ch = atoi(line + 5);
+            command_t cmd = { .type = CMD_BIND_CHANNEL, .channel = -1, .data = ch };
+            queue_push(&cmd_queue, cmd);
+        } else if (strcmp(line, "unbind") == 0) {
+            command_t cmd = { .type = CMD_UNBIND, .channel = -1, .data = 0 };
+            queue_push(&cmd_queue, cmd);
+        }
+        /* ignore unknown lines */
+    }
+    fclose(fifo);
+    return NULL;
+}
+
+int pipe_start_reader(void) {
+    /* create FIFO if it doesn't exist */
+    if (mkfifo(FIFO_PATH, 0666) != 0 && errno != EEXIST) {
+        perror("mkfifo");
+        return -1;
+    }
+    pthread_t tid;
+    if (pthread_create(&tid, NULL, pipe_thread_func, NULL) != 0) {
+        perror("pthread_create");
+        return -1;
+    }
+    pthread_detach(tid); /* we don't need to join */
+    return 0;
+}

src/pipe.h

@@ -0,0 +1,9 @@
+#ifndef PIPE_H
+#define PIPE_H
+
+/* Start the FIFO reader thread.
+ * Creates /tmp/looper_cmd (or aborts on error).
+ * Returns 0 on success, -1 on failure. */
+int pipe_start_reader(void);
+
+#endif

src/queue.c

@@ -0,0 +1,30 @@
+#include "queue.h"
+#include <stdatomic.h>
+#include <stdbool.h>
+
+void queue_init(spsc_queue_t *q) {
+    /* nothing to allocate, just ensure head/tail start at 0 */
+    q->head = 0;
+    q->tail = 0;
+}
+
+bool queue_push(spsc_queue_t *q, command_t cmd) {
+    int h = atomic_load_explicit(&q->head, memory_order_relaxed);
+    int t = atomic_load_explicit(&q->tail, memory_order_acquire);
+    int next = (h + 1) % QUEUE_CAPACITY;
+    if (next == t)
+        return false;               /* queue full */
+    q->buffer[h] = cmd;
+    atomic_store_explicit(&q->head, next, memory_order_release);
+    return true;
+}
+
+bool queue_pop(spsc_queue_t *q, command_t *cmd) {
+    int t = atomic_load_explicit(&q->tail, memory_order_relaxed);
+    int h = atomic_load_explicit(&q->head, memory_order_acquire);
+    if (t == h)
+        return false;               /* queue empty */
+    *cmd = q->buffer[t];
+    atomic_store_explicit(&q->tail, (t + 1) % QUEUE_CAPACITY, memory_order_release);
+    return true;
+}

src/queue.h

@@ -0,0 +1,31 @@
+#ifndef QUEUE_H
+#define QUEUE_H
+
+#include "command.h"
+#include <stdbool.h>
+
+/* Fixed‑size lock‑free SPSC queue (single producer, single consumer).
+ * The queue is safe for one thread writing (producer) and one thread
+ * reading (consumer).  No locks, no dynamic memory allocation.
+ * Must be initialised before first use.  All operations are RT‑safe. */
+
+#define QUEUE_CAPACITY 256
+
+typedef struct {
+    command_t  buffer[QUEUE_CAPACITY];
+    /* head: index where next element will be written (producer only)
+     * tail: index of next element to read (consumer only) */
+    int head;
+    int tail;
+} spsc_queue_t;
+
+/* Initialise queue (must be called once before any push/pop). */
+void queue_init(spsc_queue_t *q);
+
+/* Push a command.  Returns true on success, false if queue full. */
+bool queue_push(spsc_queue_t *q, command_t cmd);
+
+/* Pop a command.  Returns true if a command was retrieved, false if empty. */
+bool queue_pop(spsc_queue_t *q, command_t *cmd);
+
+#endif