X-Git-Url: https://codewiz.org/gitweb?a=blobdiff_plain;f=bertos%2Fkern%2Fpreempt.c;h=4b1ad9ee2d5dea8e213570eeb1c59fc400290fa6;hb=e62ca0b357f09804d7d894949df44224c9d74bb7;hp=9af6c0d1b402a973cc144532c15c2f1ae5d15d2f;hpb=3b33eb4b36445ee045f4cbac27f9331988205467;p=bertos.git

diff --git a/bertos/kern/preempt.c b/bertos/kern/preempt.c
index 9af6c0d1..4b1ad9ee 100644
--- a/bertos/kern/preempt.c
+++ b/bertos/kern/preempt.c
@@ -29,125 +29,115 @@
  * Copyright 2008 Bernie Innocenti <bernie@codewiz.org>
  * -->
  *
- * \brief Simple realtime multitasking scheduler.
- *        Context switching is only done cooperatively.
+ * \brief Simple preemptive multitasking scheduler.
+ *
+ * All voluntary and preemptive context switching happens on exit from
+ * a common interrupt (signal) dispatcher.  Preemption on quantum timeout
+ * is regulated by a soft-timer.  Other kinds of preemption could happen
+ * if an interrupt sends a signal to a higher priority process (but this
+ * is still unimplemented).
+ *
+ * In the POSIX implementaiton, context switching is done by the portable
+ * SVR4 swapcontext() facility.
  *
  * \version $Id: proc.c 1616 2008-08-10 19:41:26Z bernie $
  * \author Bernie Innocenti <bernie@codewiz.org>
  */
 
+#include <cfg/cfg_kern.h>
+
+#if CONFIG_KERN_PREEMPT
+
 #include "proc_p.h"
 #include "proc.h"
+#include "idle.h"
 
 #include <kern/irq.h>
+#include <kern/monitor.h>
 #include <cpu/frame.h> // CPU_IDLE
+#include <cpu/irq.h>   // IRQ_DISABLE()...
 #include <drv/timer.h>
 #include <cfg/module.h>
+#include <cfg/depend.h>    // CONFIG_DEPEND()
 
+// Check config dependencies
+CONFIG_DEPEND(CONFIG_KERN_PREEMPT,    CONFIG_KERN_SCHED && CONFIG_TIMER_EVENTS && CONFIG_KERN_IRQ);
 
-/*
- * The time sharing scheduler forces a task switch when the current
- * process has exhausted its quantum.
- */
-uint16_t Quantum;
-
-Timer preempt_timer;
+MOD_DEFINE(preempt)
 
-/**
- * Disable preemptive task switching.
- *
- * The scheduler maintains a per-process nesting counter.  Task switching is
- * effectively re-enabled only when the number of calls to proc_permit()
- * matches the number of calls to proc_forbid().
- *
- * Calling functions that could sleep while task switching is disabled
- * is dangerous, although supported.  Preemptive task switching is
- * resumed while the process is sleeping and disabled again as soon as
- * it wakes up again.
- *
- * \sa proc_permit()
- */
-void proc_forbid(void)
-{
-	/* No need to protect against interrupts here. */
-	++CurrentProcess->forbid_cnt;
-}
+/// Global preemption disabling nesting counter
+cpu_atomic_t _preempt_forbid_cnt;
 
-/**
- * Re-enable preemptive task switching.
- *
- * \sa proc_forbid()
- */
-void proc_permit(void)
-{
-	/* No need to protect against interrupts here. */
-	--CurrentProcess->forbid_cnt;
-}
+static Timer preempt_timer;
 
 
-void proc_preempt(void)
+void proc_schedule(void)
 {
-	TRACE;
+	IRQ_DISABLE;
 
-	ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+	ASSERT(proc_allowed());
+	LIST_ASSERT_VALID(&ProcReadyList);
+	CurrentProcess = (struct Process *)list_remHead(&ProcReadyList);
+	ASSERT2(CurrentProcess, "no idle proc?");
 
-	TRACEMSG("hello1");
-	IRQ_DISABLE;
-	/* Poll on the ready queue for the first ready process */
-	while (!(CurrentProcess = (struct Process *)list_remHead(&ProcReadyList)))
-	{
-	//TRACEMSG("hello2");
-		/*
-		 * Make sure we physically reenable interrupts here, no matter what
-		 * the current task status is. This is important because if we
-		 * are idle-spinning, we must allow interrupts, otherwise no
-		 * process will ever wake up.
-		 *
-		 * During idle-spinning, an interrupt can occur and it may
-		 * modify \p ProcReadyList. To ensure that compiler reload this
-		 * variable every while cycle we call CPU_MEMORY_BARRIER.
-		 * The memory barrier ensure that all variables used in this context
-		 * are reloaded.
-		 */
-		IRQ_ENABLE;
-		//FIXME: calls Qt stuff from sighandler! CPU_IDLE;
-		MEMORY_BARRIER;
-		IRQ_DISABLE;
-	//TRACEMSG("hello3");
-	}
 	IRQ_ENABLE;
-	TRACEMSG("hello4");
+
+	TRACEMSG("launching %p:%s", CurrentProcess, proc_currentName());
 }
 
-void proc_preempt_timer(UNUSED_ARG(void *, param))
+void proc_preempt(UNUSED_ARG(void *, param))
 {
-	IRQ_DISABLE;
-	if (CurrentProcess)
+	if (proc_allowed())
 	{
-		TRACEMSG("preempting %p:%s", CurrentProcess, CurrentProcess->monitor.name);
+		IRQ_DISABLE;
+
+		#if CONFIG_KERN_PRI
+			Process *rival = (Process *)LIST_HEAD(&ProcReadyList);
+			if (rival && rival->link.pri >= CurrentProcess->link.pri)
+			{
+		#endif
+
+		TRACEMSG("preempting %p:%s", CurrentProcess, proc_currentName());
+
+// FIXME: this still breaks havoc, probably because of some reentrancy issue
+#if 0
 		SCHED_ENQUEUE(CurrentProcess);
+		proc_schedule();
+#endif
+		#if CONFIG_KERN_PRI
+			}
+		#endif
+
 		IRQ_ENABLE;
-		proc_preempt();
 	}
-	IRQ_ENABLE;
 
 	timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
 	timer_add(&preempt_timer);
 }
 
-void proc_schedule(void)
+void proc_switch(void)
 {
-	TRACE;
+	ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+	TRACEMSG("%p:%s", CurrentProcess, proc_currentName());
+	ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+
+	/* Sleeping with IRQs disabled or preemption forbidden is illegal */
+	IRQ_ASSERT_ENABLED();
+	ASSERT(proc_allowed());
 
-	// Will invoke proc_preempt() in interrupt context
+	// Will invoke proc_switch() in interrupt context
 	kill(0, SIGUSR1);
 }
 
 void proc_yield(void)
 {
-	ATOMIC(SCHED_ENQUEUE(CurrentProcess));
+	TRACEMSG("%p:%s", CurrentProcess, proc_currentName());
 
-	proc_schedule();
+	IRQ_DISABLE;
+	SCHED_ENQUEUE(CurrentProcess);
+	IRQ_ENABLE;
+
+	proc_switch();
 }
 
 void proc_entry(void (*user_entry)(void))
@@ -161,9 +151,15 @@ void preempt_init(void)
 	MOD_CHECK(irq);
 	MOD_CHECK(timer);
 
-	irq_register(SIGUSR1, proc_preempt);
+	irq_register(SIGUSR1, proc_schedule);
 
-	timer_setSoftint(&preempt_timer, proc_preempt_timer, NULL);
+	timer_setSoftint(&preempt_timer, proc_preempt, NULL);
 	timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
 	timer_add(&preempt_timer);
+
+	idle_init();
+
+	MOD_INIT(preempt);
 }
+
+#endif // CONFIG_KERN_PREEMPT