nanostack-hal: remove connection from event loop init and dispatch thread

The thread flag signaling mechanism is problematic if a separate event
loop thread is not used. The problem is, that one needs to know the
thread id of the loop dispathcer, and that knowledge can be derived
only from the caller thread of the initialization function.

Remove the magic connection from caller thread to dispatcher thread
by using event flags instead of thread flags on signaling. As the
event flags require the massive amount 20 bytes of RAM whereas
thread flags requires none, keep the code behind flag.

Author: TeroJaasko

features/FEATURE_COMMON_PAL/nanostack-hal-mbed-cmsis-rtos/ns_event_loop.c

@@ -15,7 +15,17 @@
 #define TRACE_GROUP "evlp"
 
 
-#if !MBED_CONF_NANOSTACK_HAL_EVENT_LOOP_DISPATCH_FROM_APPLICATION
+#if MBED_CONF_NANOSTACK_HAL_EVENT_LOOP_DISPATCH_FROM_APPLICATION
+
+static mbed_rtos_storage_event_flags_t event_flag_cb;
+static const osEventFlagsAttr_t event_flags_attr = {
+    .name = "nanostack_event_flags",
+    .cb_mem = &event_flag_cb,
+    .cb_size = sizeof event_flag_cb
+};
+static osEventFlagsId_t event_flag_id;
+
+#else
 
 static void event_loop_thread(void *arg);
 
@@ -71,15 +81,25 @@ void eventOS_scheduler_signal(void)
     // XXX why does signal set lock if called with irqs disabled?
     //__enable_irq();
     //tr_debug("signal %p", (void*)event_thread_id);
+#if MBED_CONF_NANOSTACK_HAL_EVENT_LOOP_DISPATCH_FROM_APPLICATION
+    osEventFlagsSet(event_flag_id, 1);
+#else
     osThreadFlagsSet(event_thread_id, 1);
+#endif
     //tr_debug("signalled %p", (void*)event_thread_id);
 }
 
 void eventOS_scheduler_idle(void)
 {
     //tr_debug("idle");
     eventOS_scheduler_mutex_release();
+
+#if MBED_CONF_NANOSTACK_HAL_EVENT_LOOP_DISPATCH_FROM_APPLICATION
+    osEventFlagsWait(event_flag_id, 1, osFlagsWaitAny, osWaitForever);
+#else
     osThreadFlagsWait(1, 0, osWaitForever);
+#endif
+
     eventOS_scheduler_mutex_wait();
 }
 
@@ -99,10 +119,13 @@ void ns_event_loop_init(void)
     event_mutex_id = osMutexNew(&event_mutex_attr);
     MBED_ASSERT(event_mutex_id != NULL);
 
+    // If a separate event loop thread is not used, the signaling
+    // happens via event flags instead of thread flags. This allows one to
+    // perform the initialization from any thread and removes need to know the id
+    // of event loop dispatch thread.
 #if MBED_CONF_NANOSTACK_HAL_EVENT_LOOP_DISPATCH_FROM_APPLICATION
-    // The thread id of the current thread is stored so it can be used to signal
-    // the waiting thread from other threads or from a interrupt.
-    event_thread_id = osThreadGetId();
+    event_flag_id  = osEventFlagsNew(&event_flags_attr);
+    MBED_ASSERT(event_flag_id != NULL);
 #endif
 }