* \file
* <!--
* Copyright 2004 Develer S.r.l. (http://www.develer.com/)
- * Copyright 1999,2000,2001 Bernardo Innocenti <bernie@develer.com>
+ * Copyright 1999, 2000, 2001 Bernardo Innocenti <bernie@develer.com>
* This file is part of DevLib - See devlib/README for information.
* -->
*
* \brief IPC signals implementation.
*
- * Each process can wait for just one signal.
- * Multiple processes can wait for the same signal. In this
- * case, each signal will wake-up one of them.
+ * Signals are a low-level IPC primitive. A process receives a signal
+ * when some external event has happened. Like interrupt requests,
+ * signals do not carry any additional information. If processing a
+ * specific event requires additional data, the process must obtain it
+ * through some other mechanism.
*
- * \version $Id$
+ * Despite the name, one shouldn't confuse these signals with POSIX
+ * signals. POSIX signals are usually executed synchronously, like
+ * software interrupts.
*
- * \author Bernardo Innocenti <bernie@develer.com>
- */
-
-/*
- * $Log$
- * Revision 1.4 2004/07/30 14:30:27 rasky
- * Resa la sig_signal interrupt safe (con il nuovo scheduler IRQ-safe)
- * Rimossa event_doIntr (ora inutile) e semplificata la logica delle macro con funzioni inline
+ * In this implementation, each process has a limited set of signal
+ * bits (usually 32) and can wait for multiple signals at the same
+ * time using sig_wait(). Signals can also be polled using sig_check(),
+ * but a process spinning on its signals usually defeats their purpose
+ * of providing a multitasking-friendly infrastructure for event-driven
+ * applications.
+ *
+ * Signals are like flags: they are either active or inactive. After an
+ * external event has delivered a particular signal, it remains raised until
+ * the process acknowledges it using either sig_wait() or sig_check().
+ * Counting signals is not a reliable way to count how many times a
+ * particular event has occurred, because the same signal may be
+ * delivered twice before the process can notice.
+ *
+ * Any execution context, including an interrupt handler, can deliver
+ * a signal to a process using sig_signal(). Multiple distinct signals
+ * may be delivered at once with a single invocation of sig_signal(),
+ * although this is rarely useful.
+ *
+ * There's no hardcoded mapping of specific events to signal bits.
+ * The meaning of a particular signal bit is defined by an agreement
+ * between the delivering entity and the receiving process.
+ * For instance, a terminal driver may be written to deliver
+ * a signal bit called SIG_INT when it reads the CTRL-C sequence
+ * from the keyboard, and a process may react to it by quitting.
*
- * Revision 1.3 2004/07/30 14:24:16 rasky
- * Task switching con salvataggio perfetto stato di interrupt (SR)
- * Kernel monitor per dump informazioni su stack dei processi
+ * The SIG_SINGLE bit is reserved for a special purpose (this is
+ * more a suggestion than a constraint). When a process wants
+ * wait for a single event on the fly, it needs not allocate a
+ * free signal from its pool. Instead, SIG_SINGLE can be used
*
- * Revision 1.2 2004/06/03 11:27:09 bernie
- * Add dual-license information.
+ * The "event" module is a higher-level interface that can optionally
+ * deliver signals to processes. Messages provide even higher-level
+ * IPC services built on signals. Semaphore arbitration is also
+ * implemented using signals.
*
- * Revision 1.1 2004/05/23 17:27:00 bernie
- * Import kern/ subdirectory.
+ * Signals are very low overhead. Using them exclusively to wait
+ * for multiple asynchronous events results in very simple dispatch
+ * logic with low processor and resource usage.
*
+ *
+ * \version $Id$
+ *
+ * \author Bernardo Innocenti <bernie@develer.com>
*/
+/*#*
+ *#* $Log$
+ *#* Revision 1.7 2004/08/25 14:12:09 rasky
+ *#* Aggiornato il comment block dei log RCS
+ *#*
+ *#* Revision 1.6 2004/08/14 19:37:57 rasky
+ *#* Merge da SC: macros.h, pool.h, BIT_CHANGE, nome dei processi, etc.
+ *#*
+ *#* Revision 1.5 2004/08/04 21:50:33 bernie
+ *#* Add extensive documentation.
+ *#*
+ *#* Revision 1.4 2004/07/30 14:30:27 rasky
+ *#* Resa la sig_signal interrupt safe (con il nuovo scheduler IRQ-safe)
+ *#* Rimossa event_doIntr (ora inutile) e semplificata la logica delle macro con funzioni inline
+ *#*
+ *#* Revision 1.3 2004/07/30 14:24:16 rasky
+ *#* Task switching con salvataggio perfetto stato di interrupt (SR)
+ *#* Kernel monitor per dump informazioni su stack dei processi
+ *#*
+ *#* Revision 1.2 2004/06/03 11:27:09 bernie
+ *#* Add dual-license information.
+ *#*
+ *#* Revision 1.1 2004/05/23 17:27:00 bernie
+ *#* Import kern/ subdirectory.
+ *#*
+ *#*/
+
#include "signal.h"
#include "proc.h"
#include "proc_p.h"
#include "hw.h"
+#include <drv/kdebug.h>
// FIXME
#if CONFIG_KERN_SIGNALS
/* go to sleep and proc_schedule() another process */
CurrentProcess->sig_wait = sigs;
proc_schedule();
+
+ /* When we come back here, a signal must be arrived */
+ ASSERT(!CurrentProcess->sig_wait);
+ ASSERT(CurrentProcess->sig_recv);
}
/* Signals found: clear them and return */