preempt: document architecture

[bertos.git] / bertos / kern / preempt.c

diff --git a/bertos/kern/preempt.c b/bertos/kern/preempt.c
index 95ffbea093234e74834f5067f174fa3b90bfc956..af9555d089ba178eabfefde97e8490b09032ad6d 100644 (file)
--- a/bertos/kern/preempt.c
+++ b/bertos/kern/preempt.c
@@ -31,10 +31,23 @@
  *
  * \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"
 
@@ -44,7 +57,12 @@
 #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);
 
+MOD_DEFINE(preempt)
 
 int preempt_forbid_cnt;
 
@@ -74,11 +92,24 @@ void proc_preempt_timer(UNUSED_ARG(void *, param))
        if (!preempt_forbid_cnt)
        {
                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 break havocs, probably because of some reentrancy issue
 #if 0
                SCHED_ENQUEUE(CurrentProcess);
                proc_preempt();
 #endif
+               #if CONFIG_KERN_PRI
+                       }
+               #endif
+
                IRQ_ENABLE;
        }
 
@@ -93,7 +124,7 @@ void proc_schedule(void)
        ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
 
        /* Sleeping with IRQs disabled or preemption forbidden is illegal */
-       ASSERT_IRQ_ENABLED();
+       IRQ_ASSERT_ENABLED();
        ASSERT(preempt_forbid_cnt == 0);
 
        // Will invoke proc_preempt() in interrupt context
@@ -129,4 +160,8 @@ void preempt_init(void)
        timer_add(&preempt_timer);
 
        idle_init();
+
+       MOD_INIT(preempt);
 }
+
+#endif // CONFIG_KERN_PREEMPT