fix(split): Use queue/work for peripheral events.

* Avoid corruption by using work to process
  peripheral key position events on the main
  work thread, like local kscan events are.
* Fixes #221

app/Kconfig

@@ -94,11 +94,19 @@ config ZMK_SPLIT_BLE
 
 if ZMK_SPLIT_BLE
 
-config ZMK_SPLIT_BLE_ROLE_CENTRAL
+menuconfig ZMK_SPLIT_BLE_ROLE_CENTRAL
 	bool "Central"
 	select BT_CENTRAL
 	select BT_GATT_CLIENT
 
+if ZMK_SPLIT_BLE_ROLE_CENTRAL
+
+config ZMK_SPLIT_BLE_CENTRAL_POSITION_QUEUE_SIZE
+	int "Max number of key position state events to queue when received from peripherals"
+	default 5
+
+endif
+
 if !ZMK_SPLIT_BLE_ROLE_CENTRAL
 
 config ZMK_USB

app/src/split/bluetooth/central.c

@@ -33,9 +33,32 @@ static struct bt_uuid_128 uuid = BT_UUID_INIT_128(ZMK_SPLIT_BT_SERVICE_UUID);
 static struct bt_gatt_discover_params discover_params;
 static struct bt_gatt_subscribe_params subscribe_params;
 
-static uint8_t split_central_notify_func(struct bt_conn *conn,
-                                         struct bt_gatt_subscribe_params *params, const void *data,
-                                         uint16_t length) {
+struct zmk_split_peripheral_event {
+    uint32_t position;
+    uint32_t state;
+    int32_t timestamp;
+};
+
+K_MSGQ_DEFINE(peripheral_event_msgq, sizeof(struct zmk_split_peripheral_event),
+              CONFIG_ZMK_SPLIT_BLE_CENTRAL_POSITION_QUEUE_SIZE, 4);
+
+void peripheral_event_work_callback(struct k_work *work) {
+    struct zmk_split_peripheral_event ev;
+    while (k_msgq_get(&peripheral_event_msgq, &ev, K_NO_WAIT) == 0) {
+        struct position_state_changed *pos_ev = new_position_state_changed();
+        pos_ev->position = ev.position;
+        pos_ev->state = ev.state;
+        pos_ev->timestamp = ev.timestamp;
+
+        LOG_DBG("Trigger key position state change for %d", ev.position);
+        ZMK_EVENT_RAISE(pos_ev);
+    }
+}
+
+K_WORK_DEFINE(peripheral_event_work, peripheral_event_work_callback);
+
+static uint8_t split_central_notify_func(struct bt_conn *conn, struct bt_gatt_subscribe_params *params,
+                                      const void *data, uint16_t length) {
     static uint8_t position_state[POSITION_STATE_DATA_LEN];
 
     uint8_t changed_positions[POSITION_STATE_DATA_LEN];
@@ -58,13 +81,11 @@ static uint8_t split_central_notify_func(struct bt_conn *conn,
             if (changed_positions[i] & BIT(j)) {
                 uint32_t position = (i * 8) + j;
                 bool pressed = position_state[i] & BIT(j);
-                struct position_state_changed *pos_ev = new_position_state_changed();
-                pos_ev->position = position;
-                pos_ev->state = pressed;
-                pos_ev->timestamp = k_uptime_get();
+                struct zmk_split_peripheral_event ev = {
+                    .position = position, .state = pressed, .timestamp = k_uptime_get()};
 
-                LOG_DBG("Trigger key position state change for %d", position);
-                ZMK_EVENT_RAISE(pos_ev);
+                k_msgq_put(&peripheral_event_msgq, &ev, K_NO_WAIT);
+                k_work_submit(&peripheral_event_work);
             }
         }
     }