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/************************************************************************************
* 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 */
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