* 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 *);
struct Process *sig_proc; /* Process to be signalled */
sigbit_t sig_bit; /* Signal to send */
} Sig;
+
+ struct
+ {
+ struct Process *sig_proc; /* Process to be signalled */
+ Signal sig; /* Signal structure */
+ } SigGen;
#endif
struct
{
void event_hook_signal(Event *event);
void event_hook_softint(Event *event);
void event_hook_generic(Event *event);
-void event_hook_generic_timeout(Event *event);
+void event_hook_generic_signal(Event *event);
/** Initialize the event \a e as a no-op */
#define event_initNone(e) \
#endif
-/**
- * Prevent the compiler from optimizing access to the variable \a x, enforcing
- * a refetch from memory. This also forbid from reordering successing instances
- * of ACCESS_SAFE().
- *
- * TODO: move this to cfg/compiler.h
- */
-#define ACCESS_SAFE(x) (*(volatile typeof(x) *)&(x))
-
#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_SYSTEM5)
+#define event_initGeneric(e) \
+ ((e)->action = event_hook_generic_signal, \
+ (e)->Ev.SigGen.sig_proc = proc_current(), \
+ (e)->Ev.SigGen.sig.wait = 0, (e)->Ev.SigGen.sig.recv = 0)
#else
#define event_initGeneric(e) \
((e)->action = event_hook_generic, (e)->Ev.Gen.completed = false)
#endif
+/**
+ * Signal used to implement generic events.
+ */
+#define EVENT_GENERIC_SIGNAL SIG_SYSTEM5
+
/**
* Create a generic sleepable event.
*
/**
* 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);
+ sig_waitSignal(&e->Ev.SigGen.sig, EVENT_GENERIC_SIGNAL);
#else
while (ACCESS_SAFE(e->Ev.Gen.completed) == false)
cpu_relax();
#if CONFIG_TIMER_EVENTS
#include <drv/timer.h> /* timer_clock() */
-/* TODO: move these macros to drv/timer.h */
-#define TIMER_AFTER(x, y) ((long)(y) - (long)(x) < 0)
-#define TIMER_BEFORE(x, y) TIMER_AFTER(y, x)
-
/**
* 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_waitTimeoutSignal(&e->Ev.SigGen.sig,
+ EVENT_GENERIC_SIGNAL, 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 */
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