X-Git-Url: https://codewiz.org/gitweb?a=blobdiff_plain;f=bertos%2Fmware%2Fevent.h;h=e9f9e4a2269d01b36ec665ec85e21cc8589ff99f;hb=bd8ab60a4880319bec0f04d75a7805aa687139af;hp=83f0e13eff995182c2a18c1faa1a293f203963f7;hpb=0e3b7c98f5b8fb6f71e431791789c9370a8ae89f;p=bertos.git

diff --git a/bertos/mware/event.h b/bertos/mware/event.h
index 83f0e13e..e9f9e4a2 100644
--- a/bertos/mware/event.h
+++ b/bertos/mware/event.h
@@ -30,11 +30,63 @@
  * Copyright 1999, 2001, 2003 Bernie Innocenti <bernie@codewiz.org>
  * -->
  *
+ * \defgroup event_handling Event handling module
+ * \ingroup core
+ * \{
+ *
  * \brief Events handling
  *
  * This module implements a common system for executing
  * a user defined action calling a hook function.
  *
+ *
+ *  Device drivers often need to wait the completion of some event, usually to
+ *  allow the hardware to accomplish some asynchronous task.
+ *
+ *  A common approach is to place a busy wait with a cpu_relax() loop that invokes
+ *  the architecture-specific instructions to say that we're not doing much with
+ *  the processor.
+ *
+ *  Although technically correct, the busy loop degrades the overall system
+ *  performance in presence of multiple processes and power consumption.
+ *
+ *  With the kernel the natural way to implement such wait/complete mechanism is to
+ *  use signals via sig_wait() and sig_post()/sig_send().
+ *
+ *  However, signals in BeRTOS are only available in presence of the kernel (that
+ *  is just a compile-time option). This means that each device driver must provide
+ *  two different interfaces to implement the wait/complete semantic: one with the
+ *  kernel and another without the kernel.
+ *
+ *  The purpose of the completion events is to provide a generic interface to
+ *  implement a synchronization mechanism to block the execution of code until a
+ *  specific event happens.
+ *
+ *  This interface does not depend on the presence of the kernel and it
+ *  automatically uses the appropriate event backend to provide the same
+ *  behaviour with or without the kernel.
+ *
+ *  Example usage (wait for a generic device driver initialization):
+ *  \code
+ *  static Event e;
+ *
+ *  static void irq_handler(void)
+ *  {
+ *      // Completion event has happened, resume the execution of init()
+ *      event_do(&e);
+ *  }
+ *
+ *  static void init(void)
+ *  {
+ *      // Declare the generic completion event
+ *      event_initGeneric(&e);
+ *      // Submit the hardware initialization request
+ *      async_hw_init();
+ *      // Wait for the completion of the event
+ *      event_wait(&e);
+ *  }
+ *  \endcode
+ *
  * \author Bernie Innocenti <bernie@codewiz.org>
  */
 
@@ -57,7 +109,6 @@
 	struct Process;
 #endif
 
-
 /// User defined callback type
 typedef void (*Hook)(void *);
 
@@ -169,6 +220,10 @@ INLINE Event event_createGeneric(void)
 
 /**
  * Wait the completion of event \a e.
+ *
+ * This function releases the CPU the application is configured to use
+ * the kernel, otherwise it's just a busy wait.
+ * \note It's forbidden to use this function inside irq handling functions.
  */
 INLINE void event_wait(Event *e)
 {
@@ -192,33 +247,44 @@ INLINE void event_wait(Event *e)
 
 /**
  * Wait the completion of event \a e or \a timeout elapses.
+ *
+ * \note It's forbidden to use this function inside irq handling functions.
  */
 INLINE bool event_waitTimeout(Event *e, ticks_t timeout)
 {
+	bool ret;
+
 #if defined(CONFIG_KERN_SIGNALS) && CONFIG_KERN_SIGNALS
 	e->Ev.Sig.sig_proc = proc_current();
-	return (sig_waitTimeout(e->Ev.Sig.sig_bit, timeout) & SIG_TIMEOUT) ?
+	ret = (sig_waitTimeout(e->Ev.Sig.sig_bit, timeout) & SIG_TIMEOUT) ?
 				false : true;
 #else
 	ticks_t end = timer_clock() + timeout;
-	bool ret;
 
 	while ((ACCESS_SAFE(e->Ev.Gen.completed) == false) ||
 			TIMER_AFTER(timer_clock(), end))
 		cpu_relax();
 	ret = e->Ev.Gen.completed;
 	e->Ev.Gen.completed = false;
+#endif
 	MEMORY_BARRIER;
-
 	return ret;
-#endif
 }
 #endif /* CONFIG_TIMER_EVENTS */
 
-/** Trigger an event */
+/**
+ * Trigger an event.
+ *
+ * Execute the callback function associated with event \a e.
+ *
+ * This function can be used also in interrupt routines, but only if the
+ * event was created as a signal or generic event.
+ */
 INLINE void event_do(struct Event *e)
 {
 	e->action(e);
 }
 
+/** \} */
+
 #endif /* KERN_EVENT_H */