/************************************************************************************
 * arch/arm/src/armv6-m/exc_return.h
 *
 *   Copyright (C) 2013 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_SRC_ARMV6_M_EXC_RETURN_H
#define __ARCH_ARM_SRC_ARMV6_M_EXC_RETURN_H

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

#include <nuttx/config.h>

/************************************************************************************
 * Pre-processor Definitions
 ************************************************************************************/

/* The processor saves an EXC_RETURN value to the LR on exception entry. The
 * exception mechanism relies on this value to detect when the processor has
 * completed an exception handler.
 *
 * Bits [31:4] of an EXC_RETURN value are always 1.  When the processor loads a
 * value matching this pattern to the PC it detects that the operation is a not
 * a normal branch operation and instead, that the exception is complete.
 * Therefore, it starts the exception return sequence.
 *
 * Bits[3:0] of the EXC_RETURN value indicate the required return stack and eventual
 * processor mode.  The remaining bits of the EXC_RETURN value should be set to 1.
 */

/* EXC_RETURN_BASE: Bits that are always set in an EXC_RETURN value. */

#define EXC_RETURN_BASE          0xfffffff1

/* EXC_RETURN_PROCESS_STACK: The exception saved (and will restore) the hardware
 * context using the process stack pointer (if not set, the context was saved
 * using the main stack pointer)
 */

#define EXC_RETURN_PROCESS_BITNO (2)
#define EXC_RETURN_PROCESS_STACK (1 << EXC_RETURN_PROCESS_BITNO)

/* EXC_RETURN_THREAD_MODE: The exception will return to thread mode (if not set,
 * return stays in handler mode).
 */

#define EXC_RETURN_THREAD_BITNO  (3)
#define EXC_RETURN_THREAD_MODE   (1 << EXC_RETURN_THREAD_BITNO)

/* EXC_RETURN_HANDLER: Return to handler mode. Exception return gets state from
 * the main stack. Execution uses MSP after return.
 */

#define EXC_RETURN_HANDLER       0xfffffff1

/* EXC_RETURN_PRIVTHR: Return to privileged thread mode. Exception return gets
 * state from the main stack. Execution uses MSP after return.
 */

#define EXC_RETURN_PRIVTHR       0xfffffff9

/* EXC_RETURN_UNPRIVTHR: Return to unprivileged thread mode. Exception return gets
 * state from the process stack. Execution uses PSP after return.
 */

#define EXC_RETURN_UNPRIVTHR     0xfffffffd

/************************************************************************************
 * Inline Functions
 ************************************************************************************/

#endif  /* __ARCH_ARM_SRC_ARMV6_M_EXC_RETURN_H */

