nuttx/arch/arm/src/armv7-m/up_blocktask.c

/****************************************************************************
 * arch/arm/src/armv7-m/up_blocktask.c
 *
 *   Copyright (C) 2007-2009, 2012-2013, 2015 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdbool.h>
#include <sched.h>
#include <debug.h>

#include <nuttx/arch.h>
#include <nuttx/sched.h>

#include "sched/sched.h"
#include "up_internal.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: up_block_task
 *
 * Description:
 *   The currently executing task at the head of
 *   the ready to run list must be stopped.  Save its context
 *   and move it to the inactive list specified by task_state.
 *
 * Inputs:
 *   tcb: Refers to a task in the ready-to-run list (normally
 *     the task at the head of the list).  It most be
 *     stopped, its context saved and moved into one of the
 *     waiting task lists.  It it was the task at the head
 *     of the ready-to-run list, then a context to the new
 *     ready to run task must be performed.
 *   task_state: Specifies which waiting task list should be
 *     hold the blocked task TCB.
 *
 ****************************************************************************/

void up_block_task(struct tcb_s *tcb, tstate_t task_state)
{
  struct tcb_s *rtcb = (struct tcb_s*)g_readytorun.head;
  bool switch_needed;

  /* Verify that the context switch can be performed */

  ASSERT((tcb->task_state >= FIRST_READY_TO_RUN_STATE) &&
         (tcb->task_state <= LAST_READY_TO_RUN_STATE));

  /* Remove the tcb task from the ready-to-run list.  If we
   * are blocking the task at the head of the task list (the
   * most likely case), then a context switch to the next
   * ready-to-run task is needed. In this case, it should
   * also be true that rtcb == tcb.
   */

  switch_needed = sched_removereadytorun(tcb);

  /* Add the task to the specified blocked task list */

  sched_addblocked(tcb, (tstate_t)task_state);

  /* If there are any pending tasks, then add them to the g_readytorun
   * task list now
   */

  if (g_pendingtasks.head)
    {
      switch_needed |= sched_mergepending();
    }

  /* Now, perform the context switch if one is needed */

  if (switch_needed)
    {
      /* Update scheduler parameters */

      sched_suspend_scheduler(rtcb);

      /* Are we in an interrupt handler? */

      if (current_regs)
        {
          /* Yes, then we have to do things differently.
           * Just copy the current_regs into the OLD rtcb.
           */

          up_savestate(rtcb->xcp.regs);

          /* Restore the exception context of the rtcb at the (new) head
           * of the g_readytorun task list.
           */

          rtcb = (struct tcb_s*)g_readytorun.head;

          /* Reset scheduler parameters */

          sched_resume_scheduler(rtcb);

          /* Then switch contexts */

          up_restorestate(rtcb->xcp.regs);
        }

      /* No, then we will need to perform the user context switch */

      else
        {
          struct tcb_s *nexttcb = (struct tcb_s*)g_readytorun.head;

          /* Reset scheduler parameters */

          sched_resume_scheduler(nexttcb);

          /* Switch context to the context of the task at the head of the
           * ready to run list.
           */

          up_switchcontext(rtcb->xcp.regs, nexttcb->xcp.regs);

          /* up_switchcontext forces a context switch to the task at the
           * head of the ready-to-run list.  It does not 'return' in the
           * normal sense.  When it does return, it is because the blocked
           * task is again ready to run and has execution priority.
           */
        }
    }
}