* invalidate any other reasons why the executable file might be covered by
* the GNU General Public License.
*
- * Copyright 2008 Bernie Innocenti <bernie@codewiz.org>
- * Copyright 2009 Andrea Righi <arighi@develer.com>
- * -->
- *
- * \brief Simple preemptive multitasking scheduler.
- *
- * Preemption is explicitly regulated at the exit of each interrupt service
- * routine (ISR). Each task obtains a time quantum as soon as it is scheduled
- * on the CPU and its quantum is decremented at each clock tick. The frequency
- * of the timer determines the system tick granularity and CONFIG_KERN_QUANTUM
- * the time sharing interval.
- *
- * When the quantum expires the handler proc_needPreempt() checks if the
- * preemption is enabled and in this case preempt_schedule() is called, that
- * possibly replaces the current running thread with a different one.
- *
- * The preemption can be disabled or enabled via proc_forbid() and
- * proc_permit() primitives. This is implemented using a global atomic counter.
- * When the counter is greater than 0 the task cannot be preempted; only when
- * the counter reaches 0 the task can be preempted again.
- *
- * Preemption-disabled sections may be nested. The preemption will be
- * re-enabled when the outermost preemption-disabled section completes.
- *
- * The voluntary preemption still happens via proc_switch() or proc_yield().
- * The first one assumes the current process has been already added to a
- * private wait queue (e.g., on a semaphore or a signal), while the second one
- * takes care of adding the process into the ready queue.
- *
- * Context switch is done by CPU-dependent support routines. In case of a
- * voluntary preemption the context switch routine must take care of
- * saving/restoring only the callee-save registers (the voluntary-preemption is
- * actually a function call). The kernel-preemption always happens inside a
- * signal/interrupt context and it must take care of saving all registers. For
- * this, in the entry point of each ISR the caller-save registers must be
- * saved. In the ISR exit point, if the context switch must happen, we switch
- * to user-context and call the same voluntary context switch routine that take
- * care of saving/restoring also the callee-save registers. On resume from the
- * switch, the interrupt exit point moves back to interrupt-context, resumes
- * the caller-save registers (saved in the ISR entry point) and return from the
- * interrupt-context.
- *
- * \note Thread priority (if enabled by CONFIG_KERN_PRI) defines the order in
- * the \p proc_ready_list and the capability to deschedule a running process. A
- * low-priority thread can't preempt a high-priority thread.
- *
- * A high-priority process can preempt a low-priority process immediately (it
- * will be descheduled and replaced in the interrupt exit point). Processes
- * running at the same priority can be descheduled when they expire the time
- * quantum.
- *
- * \note Sleeping while preemption is disabled fallbacks to a busy-wait sleep.
- * Voluntary preemption when preemption is disabled raises a kernel bug.
- *
- * \author Bernie Innocenti <bernie@codewiz.org>
- * \author Andrea Righi <arighi@develer.com>
- */
-
-#include "cfg/cfg_proc.h"
-
-#include "proc_p.h"
-#include "proc.h"
-
-#include <kern/irq.h>
-#include <kern/monitor.h>
-#include <cpu/frame.h> // CPU_IDLE
-#include <cpu/irq.h> // IRQ_DISABLE()...
-#include <cfg/log.h>
-#include <cfg/module.h>
-#include <cfg/depend.h> // CONFIG_DEPEND()
-
-// Check config dependencies
-CONFIG_DEPEND(CONFIG_KERN_PREEMPT, CONFIG_KERN);
-
-MOD_DEFINE(preempt)
-
-/* Global preemption nesting counter */
-cpu_atomic_t preempt_count;
-
-/*
- * The time sharing interval: when a process is scheduled on a CPU it gets an
- * amount of CONFIG_KERN_QUANTUM clock ticks. When these ticks expires and
- * preemption is enabled a new process is selected to run.
- */
-int _proc_quantum;
-
-/**
- * Define function prototypes exported outside.
+ * \note This file is deprecated and kept only for backward compatibility.
*
- * Required to silent gcc "no previous prototype" warnings.
- */
-void preempt_yield(void);
-int preempt_needPreempt(void);
-void preempt_preempt(void);
-void preempt_switch(void);
-void preempt_wakeup(Process *proc);
-void preempt_init(void);
-
-/**
- * Call the scheduler and eventually replace the current running process.
- */
-static void preempt_schedule(void)
-{
- _proc_quantum = CONFIG_KERN_QUANTUM;
- proc_schedule();
-}
-
-/**
- * Check if we need to schedule another task
- */
-int preempt_needPreempt(void)
-{
- if (UNLIKELY(current_process == NULL))
- return 0;
- if (!proc_preemptAllowed())
- return 0;
- if (LIST_EMPTY(&proc_ready_list))
- return 0;
- return _proc_quantum ? prio_next() > prio_curr() :
- prio_next() >= prio_curr();
-}
-
-/**
- * Preempt the current task.
- */
-void preempt_preempt(void)
-{
- IRQ_ASSERT_DISABLED();
- ASSERT(current_process);
-
- /* Perform the kernel preemption */
- LOG_INFO("preempting %p:%s\n", current_process, proc_currentName());
- /* We are inside a IRQ context, so ATOMIC is not needed here */
- SCHED_ENQUEUE(current_process);
- preempt_schedule();
-}
-
-/**
- * Give the control of the CPU to another process.
- *
- * \note Assume the current process has been already added to a wait queue.
- *
- * \warning This should be considered an internal kernel function, even if it
- * is allowed, usage from application code is strongly discouraged.
- */
-void preempt_switch(void)
-{
- ASSERT(proc_preemptAllowed());
-
- ATOMIC(preempt_schedule());
-}
-
-/**
- * Immediately wakeup a process, dispatching it to the CPU.
- */
-void preempt_wakeup(Process *proc)
-{
- ASSERT(proc_preemptAllowed());
- ASSERT(current_process);
- IRQ_ASSERT_DISABLED();
-
- if (prio_proc(proc) >= prio_curr())
- {
- Process *old_process = current_process;
-
- SCHED_ENQUEUE(current_process);
- _proc_quantum = CONFIG_KERN_QUANTUM;
- current_process = proc;
- proc_switchTo(current_process, old_process);
- }
- else
- SCHED_ENQUEUE_HEAD(proc);
-}
-
-/**
- * Voluntarily release the CPU.
+ * -->
*/
-void preempt_yield(void)
-{
- /*
- * Voluntary preemption while preemption is disabled is considered
- * illegal, as not very useful in practice.
- *
- * ASSERT if it happens.
- */
- ASSERT(proc_preemptAllowed());
- IRQ_ASSERT_ENABLED();
-
- ATOMIC(
- SCHED_ENQUEUE(current_process);
- preempt_schedule();
- );
-}
-
-void preempt_init(void)
-{
- MOD_INIT(preempt);
-}
projects / bertos.git / blobdiff