* 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>
*/
struct Process;
#endif
-
/// User defined callback type
typedef void (*Hook)(void *);
#if defined(CONFIG_KERN_SIGNALS) && CONFIG_KERN_SIGNALS
/** Initialize the generic sleepable event \a e */
#define event_initGeneric(e) \
- event_initSignal(e, proc_current(), SIG_SINGLE)
+ event_initSignal(e, proc_current(), SIG_SYSTEM5)
#else
#define event_initGeneric(e) \
((e)->action = event_hook_generic, (e)->Ev.Gen.completed = false)
/**
* 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)
{
#if defined(CONFIG_KERN_SIGNALS) && CONFIG_KERN_SIGNALS
+ e->Ev.Sig.sig_proc = proc_current();
sig_wait(e->Ev.Sig.sig_bit);
#else
while (ACCESS_SAFE(e->Ev.Gen.completed) == false)
cpu_relax();
+ e->Ev.Gen.completed = false;
+ MEMORY_BARRIER;
#endif
}
/**
* 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
- return (sig_waitTimeout(e->Ev.Sig.sig_bit, timeout) & SIG_TIMEOUT) ?
+ e->Ev.Sig.sig_proc = proc_current();
+ ret = (sig_waitTimeout(e->Ev.Sig.sig_bit, timeout) & SIG_TIMEOUT) ?
false : true;
#else
ticks_t end = timer_clock() + timeout;
while ((ACCESS_SAFE(e->Ev.Gen.completed) == false) ||
TIMER_AFTER(timer_clock(), end))
cpu_relax();
-
- return e->Ev.Gen.completed;
+ ret = e->Ev.Gen.completed;
+ e->Ev.Gen.completed = false;
#endif
+ MEMORY_BARRIER;
+ return ret;
}
#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 */