proc: Split cooperative scheduler in coop.c

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

diff --git a/bertos/kern/coop.c b/bertos/kern/coop.c
new file mode 100644 (file)
index 0000000..b62a02e
--- /dev/null
+++ b/bertos/kern/coop.c
@@ -0,0 +1,141 @@
+/**
+ * \file
+ * <!--
+ * This file is part of BeRTOS.
+ *
+ * Bertos is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As a special exception, you may use this file as part of a free software
+ * library without restriction.  Specifically, if other files instantiate
+ * templates or use macros or inline functions from this file, or you compile
+ * this file and link it with other files to produce an executable, this
+ * file does not by itself cause the resulting executable to be covered by
+ * the GNU General Public License.  This exception does not however
+ * invalidate any other reasons why the executable file might be covered by
+ * the GNU General Public License.
+ *
+ * Copyright 2001, 2004, 2008 Develer S.r.l. (http://www.develer.com/)
+ * Copyright 1999, 2000, 2001 Bernie Innocenti <bernie@codewiz.org>
+ * -->
+ *
+ * \brief Simple realtime multitasking scheduler.
+ *        Context switching is only done cooperatively.
+ *
+ * \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"
+
+// Log settings for cfg/log.h.
+#define LOG_LEVEL   KERN_LOG_LEVEL
+#define LOG_FORMAT  KERN_LOG_FORMAT
+#include <cfg/log.h>
+
+#include <cpu/irq.h>
+#include <cpu/types.h>
+#include <cpu/attr.h>
+#include <cpu/frame.h>
+
+/**
+ * CPU dependent context switching routines.
+ *
+ * Saving and restoring the context on the stack is done by a CPU-dependent
+ * support routine which usually needs to be written in assembly.
+ */
+EXTERN_C void asm_switch_context(cpustack_t **new_sp, cpustack_t **save_sp);
+
+
+/**
+ * System scheduler: pass CPU control to the next process in
+ * the ready queue.
+ */
+void proc_schedule(void)
+{
+       struct Process *old_process;
+       cpuflags_t flags;
+
+       ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+       ASSERT_USER_CONTEXT();
+       ASSERT_IRQ_ENABLED();
+
+       /* Remember old process to save its context later */
+       old_process = CurrentProcess;
+
+       /* Poll on the ready queue for the first ready process */
+       IRQ_SAVE_DISABLE(flags);
+       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.
+                * \todo If there was a way to write sig_wait() so that it does not
+                * disable interrupts while waiting, there would not be any
+                * reason to do this.
+                */
+               IRQ_ENABLE;
+               CPU_IDLE;
+               MEMORY_BARRIER;
+               IRQ_DISABLE;
+       }
+       IRQ_RESTORE(flags);
+
+       /*
+        * Optimization: don't switch contexts when the active
+        * process has not changed.
+        */
+       if (CurrentProcess != old_process)
+       {
+               cpustack_t *dummy;
+
+               #if CONFIG_KERN_MONITOR
+                       LOG_INFO("Switch from %p(%s) to %p(%s)\n",
+                               old_process,    old_process ? old_process->monitor.name : "NONE",
+                               CurrentProcess, CurrentProcess->monitor.name);
+               #endif
+
+               /* Save context of old process and switch to new process. If there is no
+                * old process, we save the old stack pointer into a dummy variable that
+                * we ignore. In fact, this happens only when the old process has just
+                * exited.
+                * TODO: Instead of physically clearing the process at exit time, a zombie
+                * list should be created.
+                */
+               asm_switch_context(&CurrentProcess->stack, old_process ? &old_process->stack : &dummy);
+       }
+
+       /* This RET resumes the execution on the new process */
+}
+
+
+/**
+ * Co-operative context switch
+ */
+void proc_switch(void)
+{
+       ATOMIC(SCHED_ENQUEUE(CurrentProcess));
+
+       proc_schedule();
+}