text: /****************************************************************************
   *  arch/risc-v/src/common/riscv_idle.c
   *
   *   Copyright (C) 2011-2012, 2016 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 <nuttx/irq.h>
  #include <nuttx/arch.h>
  
  #include "riscv_internal.h"
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: up_idle
   *
   * Description:
   *   up_idle() is the logic that will be executed when there is no other
   *   ready-to-run task.  This is processor idle time and will continue until
   *   some interrupt occurs to cause a context switch from the idle task.
   *
   *   Processing in this state may be processor-specific. e.g., this is where
   *   power management operations might be performed.
   *
   ****************************************************************************/
  
  void up_idle(void)
  {
  #if defined(CONFIG_SUPPRESS_INTERRUPTS) || defined(CONFIG_SUPPRESS_TIMER_INTS)
    /* If the system is idle and there are no timer interrupts, then process
     * "fake" timer interrupts. Hopefully, something will wake up.
     */
  
    nxsched_process_timer();
  #else
  
    /* This would be an appropriate place to put some MCU-specific logic to
     * sleep in a reduced power mode until an interrupt occurs to save power
     */
  
    /* This is a kludge that I still don't understand.  The call to
     * kmm_trysemaphore() in the nx_start.c IDLE loop seems necessary for the
     * good health of the IDLE loop.  When the work queue is enabled, this
     * logic is removed from the IDLE loop and it appears that we are somehow
     * left idling with interrupts non-functional. The following should be
     * no-op, it just disables then re-enables interrupts.  But it fixes the
     * problem and will stay here until I understand the problem/fix better.
     */
  
  #ifdef CONFIG_SCHED_WORKQUEUE
    irqstate_t flags = enter_critical_section();
    leave_critical_section(flags);
  #endif
  #endif
  }
  