* 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.
*
- * \version $Id$
+ *
+ * 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>
*/
#include <cfg/compiler.h>
#include "cfg/cfg_proc.h"
#include "cfg/cfg_signal.h"
+#include "cfg/cfg_timer.h"
+
+#include <cpu/power.h> /* cpu_relax() */
#if CONFIG_KERN
#if defined(CONFIG_KERN_SIGNALS) && CONFIG_KERN_SIGNALS
struct Process;
#endif
-
/// User defined callback type
typedef void (*Hook)(void *);
Hook func; /* Pointer to softint hook */
void *user_data; /* Data to be passed back to user hook */
} Int;
+
+ struct
+ {
+ bool completed; /* Generic event completion */
+ } Gen;
} Ev;
} Event;
void event_hook_ignore(Event *event);
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);
/** Initialize the event \a e as a no-op */
#define event_initNone(e) \
#endif
-/** Trigger an event */
+/**
+ * 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)
+#else
+#define event_initGeneric(e) \
+ ((e)->action = event_hook_generic, (e)->Ev.Gen.completed = false)
+#endif
+
+/**
+ * Create a generic sleepable event.
+ *
+ * \return the properly initialized generic event structure.
+ */
+INLINE Event event_createGeneric(void)
+{
+ Event e;
+ event_initGeneric(&e);
+ return e;
+}
+
+/**
+ * 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
+}
+
+#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();
+ 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();
+ ret = e->Ev.Gen.completed;
+ e->Ev.Gen.completed = false;
+#endif
+ MEMORY_BARRIER;
+ return ret;
+}
+#endif /* CONFIG_TIMER_EVENTS */
+
+/**
+ * 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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