text: /****************************************************************************
   * arch/arm/include/spinlock.h
   *
   *   Copyright (C) 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.
   *
   ****************************************************************************/
  
  #ifndef __ARCH_ARM_INCLUDE_SPINLOCK_H
  #define __ARCH_ARM_INCLUDE_SPINLOCK_H
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #ifndef __ASSEMBLY__
  #  include <stdint.h>
  #endif /* __ASSEMBLY__ */
  
  /****************************************************************************
   * Pre-processor Definitions
   ****************************************************************************/
  
  #define SP_UNLOCKED 0  /* The Un-locked state */
  #define SP_LOCKED   1  /* The Locked state */
  
  /****************************************************************************
   * Public Types
   ****************************************************************************/
  
  #ifndef __ASSEMBLY__
  
  /* The Type of a spinlock.
   *
   * ARMv6 architecture introuced the concept of exclusive accesses to memory
   * locations in the form of the Load-Exclusive (LDREX) and Store-Exclusive
   * (STREX) instructions in ARM and Thumb instruction sets.  ARMv6K extended
   * this to included byte, halfword, and doubleword variants of LDREX and
   * STREX.  ARMv7-M supports byte and halfwor, but not the doudleword varient
   * (ARMv6-M does not support exlusive access)
   *
   * ARM architectures prior to ARMv6 supported SWP and SWPB instructions that
   * atomically swap a 32-bit word for byte value between a register and a
   * memory location.  From the ARMv6 architecture, ARM deprecates the use
   * of SWP and SWPB.
   */
  
  typedef uint8_t spinlock_t;
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: up_testset
   *
   * Description:
   *   Perform an atomic test and set operation on the provided spinlock.
   *
   *   This function must be provided via the architecture-specific logoic.
   *
   * Input Parameters:
   *   lock - The address of spinlock object.
   *
   * Returned Value:
   *   The spinlock is always locked upon return.  The value of previous value
   *   of the spinlock variable is returned, either SP_LOCKED if the spinlock
   *   as previously locked (meaning that the test-and-set operation failed to
   *   obtain the lock) or SP_UNLOCKED if the spinlock was previously unlocked
   *   (meaning that we successfully obtained the lock)
   *
   ****************************************************************************/
  
  /* See prototype in nuttx/include/nuttx/spinlock.h */
  
  #endif /* __ASSEMBLY__ */
  #endif /* __ARCH_ARM_INCLUDE_SPINLOCK_H */
  