X-Git-Url: https://codewiz.org/gitweb?a=blobdiff_plain;f=bertos%2Fkern%2Fpreempt.c;h=4b1ad9ee2d5dea8e213570eeb1c59fc400290fa6;hb=e62ca0b357f09804d7d894949df44224c9d74bb7;hp=825505019aebeae98ed03f7efe77bc383ecd385a;hpb=6db1e5bb5ee9abb34b1f0b0c40cb82c6143b7bae;p=bertos.git

diff --git a/bertos/kern/preempt.c b/bertos/kern/preempt.c
index 82550501..4b1ad9ee 100644
--- a/bertos/kern/preempt.c
+++ b/bertos/kern/preempt.c
@@ -31,6 +31,15 @@
  *
  * \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>
  */
@@ -41,6 +50,7 @@
 
 #include "proc_p.h"
 #include "proc.h"
+#include "idle.h"
 
 #include <kern/irq.h>
 #include <kern/monitor.h>
@@ -52,24 +62,20 @@
 
 // Check config dependencies
 CONFIG_DEPEND(CONFIG_KERN_PREEMPT,    CONFIG_KERN_SCHED && CONFIG_TIMER_EVENTS && CONFIG_KERN_IRQ);
-CONFIG_DEPEND(CONFIG_KERN_PRI,        CONFIG_KERN_PREEMPT);
 
 MOD_DEFINE(preempt)
 
-int preempt_forbid_cnt;
+/// Global preemption disabling nesting counter
+cpu_atomic_t _preempt_forbid_cnt;
 
 static Timer preempt_timer;
 
 
-// fwd decl from idle.c
-void idle_init(void);
-
-
-void proc_preempt(void)
+void proc_schedule(void)
 {
 	IRQ_DISABLE;
 
-	ASSERT(preempt_forbid_cnt == 0);
+	ASSERT(proc_allowed());
 	LIST_ASSERT_VALID(&ProcReadyList);
 	CurrentProcess = (struct Process *)list_remHead(&ProcReadyList);
 	ASSERT2(CurrentProcess, "no idle proc?");
@@ -79,9 +85,9 @@ void proc_preempt(void)
 	TRACEMSG("launching %p:%s", CurrentProcess, proc_currentName());
 }
 
-void proc_preempt_timer(UNUSED_ARG(void *, param))
+void proc_preempt(UNUSED_ARG(void *, param))
 {
-	if (!preempt_forbid_cnt)
+	if (proc_allowed())
 	{
 		IRQ_DISABLE;
 
@@ -92,9 +98,11 @@ void proc_preempt_timer(UNUSED_ARG(void *, param))
 		#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_preempt();
+		proc_schedule();
 #endif
 		#if CONFIG_KERN_PRI
 			}
@@ -107,17 +115,17 @@ void proc_preempt_timer(UNUSED_ARG(void *, param))
 	timer_add(&preempt_timer);
 }
 
-void proc_schedule(void)
+void proc_switch(void)
 {
 	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 */
-	ASSERT_IRQ_ENABLED();
-	ASSERT(preempt_forbid_cnt == 0);
+	IRQ_ASSERT_ENABLED();
+	ASSERT(proc_allowed());
 
-	// Will invoke proc_preempt() in interrupt context
+	// Will invoke proc_switch() in interrupt context
 	kill(0, SIGUSR1);
 }
 
@@ -129,7 +137,7 @@ void proc_yield(void)
 	SCHED_ENQUEUE(CurrentProcess);
 	IRQ_ENABLE;
 
-	proc_schedule();
+	proc_switch();
 }
 
 void proc_entry(void (*user_entry)(void))
@@ -143,9 +151,9 @@ 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);