preempt: introduce idle process; timer: use managed irqs for preemption

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

diff --git a/bertos/kern/preempt.c b/bertos/kern/preempt.c
index dfa343d7a9b702c769a590d8b76e0a409bdec9e2..7ecd481d0cdf57c6d4c3679fc4ccfa43f5cc794e 100644 (file)
--- a/bertos/kern/preempt.c
+++ b/bertos/kern/preempt.c
@@ -26,31 +26,27 @@
  * invalidate any other reasons why the executable file might be covered by
  * the GNU General Public License.
  *
- * Copyright 2001, 2004 Develer S.r.l. (http://www.develer.com/)
- * Copyright 1999, 2000, 2001, 2008 Bernie Innocenti <bernie@codewiz.org>
+ * Copyright 2008 Bernie Innocenti <bernie@codewiz.org>
  * -->
  *
- * \brief Simple realtime multitasking scheduler.
- *        Context switching is only done cooperatively.
+ * \brief Simple preemptive multitasking scheduler.
  *
  * \version $Id: proc.c 1616 2008-08-10 19:41:26Z bernie $
  * \author Bernie Innocenti <bernie@codewiz.org>
- * \author Stefano Fedrigo <aleph@develer.com>
  */
 
 #include "proc_p.h"
 #include "proc.h"
 
+#include <kern/irq.h>
+#include <kern/monitor.h>
 #include <cpu/frame.h> // CPU_IDLE
+#include <drv/timer.h>
+#include <cfg/module.h>
 
-#include <unistd.h> // XXX alarm()
 
 
-/*
- * The time sharing scheduler forces a task switch when the current
- * process has exhausted its quantum.
- */
-uint16_t Quantum;
+Timer preempt_timer;
 
 /**
  * Disable preemptive task switching.
@@ -83,104 +79,99 @@ void proc_permit(void)
        --CurrentProcess->forbid_cnt;
 }
 
-static void (*irq_handlers[100])(void); // FIXME
-
 
 void proc_preempt(void)
 {
-       TRACE;
+       IRQ_DISABLE;
 
-       ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+       LIST_ASSERT_VALID(&ProcReadyList);
+       CurrentProcess = (struct Process *)list_remHead(&ProcReadyList);
+       LIST_ASSERT_VALID(&ProcReadyList);
+       ASSERT2(CurrentProcess, "no idle proc?");
 
-       IRQ_DISABLE;
-       /* Poll on the ready queue for the first ready process */
-       while (!(CurrentProcess = (struct Process *)list_remHead(&ProcReadyList)))
-       {
-               /*
-                * 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;
-               CPU_IDLE;
-               MEMORY_BARRIER;
-               IRQ_DISABLE;
-       }
        IRQ_ENABLE;
+
+       TRACEMSG("new proc: %p:%s", CurrentProcess, CurrentProcess ? CurrentProcess->monitor.name : "---");
+       monitor_report();
 }
 
-void proc_preempt_timer(void)
+void proc_preempt_timer(UNUSED_ARG(void *, param))
 {
-       // TODO: check Quantum
+       IRQ_DISABLE;
+/*
+       if (!CurrentProcess->forbid_cnt)
+       {
+               TRACEMSG("preempting %p:%s", CurrentProcess, CurrentProcess->monitor.name);
+               LIST_ASSERT_VALID(&ProcReadyList);
+               SCHED_ENQUEUE(CurrentProcess);
+               proc_preempt();
+       }
+*/
+       IRQ_ENABLE;
 
-       alarm(1);
-       ATOMIC(SCHED_ENQUEUE(CurrentProcess));
-       proc_schedule();
+       timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
+       timer_add(&preempt_timer);
 }
 
 void proc_schedule(void)
 {
+       TRACE;
+
+       // Will invoke proc_preempt() in interrupt context
        kill(0, SIGUSR1);
 }
 
 void proc_yield(void)
 {
-       ATOMIC(SCHED_ENQUEUE(CurrentProcess));
+       TRACE;
 
+       ASSERT_IRQ_ENABLED();
+       IRQ_DISABLE;
+       SCHED_ENQUEUE(CurrentProcess);
+       LIST_ASSERT_VALID(&ProcReadyList);
        proc_schedule();
+       IRQ_ENABLE;
 }
 
-/* signal handler */
-void irq_entry(int signum)
+void proc_entry(void (*user_entry)(void))
 {
-       Process *old_process;
-
-       TRACEMSG("storing %p:%s", CurrentProcess, CurrentProcess->monitor.name);
-       CurrentProcess->leaving = false;
-       getcontext(&CurrentProcess->context);
-       /* We get here in two ways: directly, and after setcontext() below */
-
-       if (CurrentProcess->leaving)
-       {
-               TRACEMSG("leaving to %p:%s", CurrentProcess, CurrentProcess->monitor.name);
-               return;
-       }
+       user_entry();
+       proc_exit();
+}
 
-       old_process = CurrentProcess;
 
-       irq_handlers[signum]();
+static cpustack_t idle_stack[CONFIG_PROC_DEFSTACKSIZE / sizeof(cpustack_t)];
 
-       if (old_process != CurrentProcess)
+/*
+ * The idle process
+ *
+ * This process never dies and never sleeps.  It's also quite apathic
+ * and a bit antisocial.
+ *
+ * Having an idle process costs some stack space, but simplifies the
+ * interrupt-driven preemption logic because there is always a user
+ * context to which we can return.
+ */
+static NORETURN void idle(void)
+{
+       for (;;)
        {
-               TRACEMSG("launching %p:%s", CurrentProcess, CurrentProcess->monitor.name);
-               CurrentProcess->leaving = true;
-               setcontext(&CurrentProcess->context);
-               /* not reached */
+               TRACE;
+               monitor_report();
+               proc_yield(); // FIXME: CPU_IDLE
        }
-
-       TRACEMSG("keeping %p:%s", CurrentProcess, CurrentProcess->monitor.name);
 }
 
 void preempt_init(void)
 {
-       struct sigaction act;
-       act.sa_handler = irq_entry;
-       sigemptyset(&act.sa_mask);
-       sigaddset(&act.sa_mask, SIGUSR1);
-       sigaddset(&act.sa_mask, SIGALRM);
-       act.sa_flags = SA_RESTART; /* | SA_SIGINFO; */
-
-       irq_handlers[SIGUSR1] = proc_preempt;
-       irq_handlers[SIGALRM] = proc_preempt_timer;
-       sigaction(SIGUSR1, &act, NULL);
-       sigaction(SIGALRM, &act, NULL);
-
-       alarm(1);  // FIXME
+       MOD_CHECK(irq);
+       MOD_CHECK(timer);
+
+       irq_register(SIGUSR1, proc_preempt);
+
+       timer_setSoftint(&preempt_timer, proc_preempt_timer, NULL);
+       timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
+       timer_add(&preempt_timer);
+
+       proc_new(idle, NULL, sizeof(idle_stack), idle_stack);
 }