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## root / include / libdragonfly / atomic.h @ 1554

 1 /* This file is in the dragonfly library directory because it seems to be   missing from the AVR libc distribution */    /* Copyright (c) 2007 Dean Camera   All rights reserved.     Redistribution and use in source and binary forms, with or without   modification, are permitted provided that the following conditions are met:     * Redistributions of source code must retain the above copyright   notice, this list of conditions and the following disclaimer.     * 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.     * Neither the name of the copyright holders nor the names of   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.  */  /* $Id: atomic.h,v 1.3 2007/12/20 14:17:56 joerg_wunsch Exp$ */  #ifndef _UTIL_ATOMIC_H_  #define _UTIL_ATOMIC_H_ 1  #include  #include  #if !defined(__DOXYGEN__)  /* Internal helper functions. */  static __inline__ uint8_t __iSeiRetVal(void)  {   sei();   return 1;  }  static __inline__ uint8_t __iCliRetVal(void)  {   cli();   return 1;  }  static __inline__ void __iSeiParam(const uint8_t *__s)  {   sei();   __asm__ volatile ("" ::: "memory");   (void)__s;  }  static __inline__ void __iCliParam(const uint8_t *__s)  {   cli();   __asm__ volatile ("" ::: "memory");   (void)__s;  }  static __inline__ void __iRestore(const uint8_t *__s)  {   SREG = *__s;   __asm__ volatile ("" ::: "memory");  }  #endif /* !__DOXYGEN__ */  /** \file */  /** \defgroup util_atomic Atomically and Non-Atomically Executed Code Blocks     \code   #include   \endcode     \note The macros in this header file require the ISO/IEC 9899:1999   ("ISO C99") feature of for loop variables that are declared inside   the for loop itself. For that reason, this header file can only   be used if the standard level of the compiler (option --std=) is   set to either \c c99 or \c gnu99.     The macros in this header file deal with code blocks that are   guaranteed to be excuted Atomically or Non-Atmomically. The term   "Atomic" in this context refers to the unability of the respective   code to be interrupted.     These macros operate via automatic manipulation of the Global   Interrupt Status (I) bit of the SREG register. Exit paths from   both block types are all managed automatically without the need   for special considerations, i. e. the interrupt status will be   restored to the same value it has been when entering the   respective block.     A typical example that requires atomic access is a 16 (or more)   bit variable that is shared between the main execution path and an   ISR. While declaring such a variable as volatile ensures that the   compiler will not optimize accesses to it away, it does not   guarantee atomic access to it. Assuming the following example:     \code  #include  #include  #include    volatile uint16_t ctr;    ISR(TIMER1_OVF_vect)  {   ctr--;  }    ...  int  main(void)  {   ...   ctr = 0x200;   start_timer();   while (ctr != 0)   // wait   ;   ...  }   \endcode     There is a chance where the main context will exit its wait loop   when the variable \c ctr just reached the value 0xFF. This happens   because the compiler cannot natively access a 16-bit variable   atomically in an 8-bit CPU. So the variable is for example at   0x100, the compiler then tests the low byte for 0, which succeeds.   It then proceeds to test the high byte, but that moment the ISR   triggers, and the main context is interrupted. The ISR will   decrement the variable from 0x100 to 0xFF, and the main context   proceeds. It now tests the high byte of the variable which is   (now) also 0, so it concludes the variable has reached 0, and   terminates the loop.     Using the macros from this header file, the above code can be   rewritten like:     \code  #include  #include  #include  #include    volatile uint16_t ctr;    ISR(TIMER1_OVF_vect)  {   ctr--;  }    ...  int  main(void)  {   ...   ctr = 0x200;   start_timer();   sei();   uint16_t ctr_copy;   do   {   ATOMIC_BLOCK(ATOMIC_FORCEON)   {   ctr_copy = ctr;   }   }   while (ctr_copy != 0);   ...  }   \endcode     This will install the appropriate interrupt protection before   accessing variable \c ctr, so it is guaranteed to be consistently   tested. If the global interrupt state were uncertain before   entering the ATOMIC_BLOCK, it should be executed with the   parameter ATOMIC_RESTORESTATE rather than ATOMIC_FORCEON.    */  /** \def ATOMIC_BLOCK(type)   \ingroup util_atomic     Creates a block of code that is guaranteed to be executed   atomically. Upon entering the block the Global Interrupt Status   flag in SREG is disabled, and re-enabled upon exiting the block   from any exit path.     Two possible macro parameters are permitted, ATOMIC_RESTORESTATE   and ATOMIC_FORCEON.  */  #if defined(__DOXYGEN__)  #define ATOMIC_BLOCK(type)  #else  #define ATOMIC_BLOCK(type) for ( type, __ToDo = __iCliRetVal(); \   __ToDo ; __ToDo = 0 )  #endif /* __DOXYGEN__ */  /** \def NONATOMIC_BLOCK(type)   \ingroup util_atomic     Creates a block of code that is executed non-atomically. Upon   entering the block the Global Interrupt Status flag in SREG is   enabled, and disabled upon exiting the block from any exit   path. This is useful when nested inside ATOMIC_BLOCK sections,   allowing for non-atomic execution of small blocks of code while   maintaining the atomic access of the other sections of the parent   ATOMIC_BLOCK.     Two possible macro parameters are permitted,   NONATOMIC_RESTORESTATE and NONATOMIC_FORCEOFF.  */  #if defined(__DOXYGEN__)  #define NONATOMIC_BLOCK(type)  #else  #define NONATOMIC_BLOCK(type) for ( type, __ToDo = __iSeiRetVal(); \   __ToDo ; __ToDo = 0 )  #endif /* __DOXYGEN__ */  /** \def ATOMIC_RESTORESTATE   \ingroup util_atomic     This is a possible parameter for ATOMIC_BLOCK. When used, it will   cause the ATOMIC_BLOCK to restore the previous state of the SREG   register, saved before the Global Interrupt Status flag bit was   disabled. The net effect of this is to make the ATOMIC_BLOCK's   contents guaranteed atomic, without changing the state of the   Global Interrupt Status flag when execution of the block   completes.  */  #if defined(__DOXYGEN__)  #define ATOMIC_RESTORESTATE  #else  #define ATOMIC_RESTORESTATE uint8_t sreg_save \   __attribute__((__cleanup__(__iRestore))) = SREG  #endif /* __DOXYGEN__ */  /** \def ATOMIC_FORCEON   \ingroup util_atomic     This is a possible parameter for ATOMIC_BLOCK. When used, it will   cause the ATOMIC_BLOCK to force the state of the SREG register on   exit, enabling the Global Interrupt Status flag bit. This saves on   flash space as the previous value of the SREG register does not   need to be saved at the start of the block.     Care should be taken that ATOMIC_FORCEON is only used when it is   known that interrupts are enabled before the block's execution or   when the side effects of enabling global interrupts at the block's   completion are known and understood.  */  #if defined(__DOXYGEN__)  #define ATOMIC_FORCEON  #else  #define ATOMIC_FORCEON uint8_t sreg_save \   __attribute__((__cleanup__(__iSeiParam))) = 0  #endif /* __DOXYGEN__ */  /** \def NONATOMIC_RESTORESTATE   \ingroup util_atomic     This is a possible parameter for NONATOMIC_BLOCK. When used, it   will cause the NONATOMIC_BLOCK to restore the previous state of   the SREG register, saved before the Global Interrupt Status flag   bit was enabled. The net effect of this is to make the   NONATOMIC_BLOCK's contents guaranteed non-atomic, without changing   the state of the Global Interrupt Status flag when execution of   the block completes.  */  #if defined(__DOXYGEN__)  #define NONATOMIC_RESTORESTATE  #else  #define NONATOMIC_RESTORESTATE uint8_t sreg_save \   __attribute__((__cleanup__(__iRestore))) = SREG  #endif /* __DOXYGEN__ */  /** \def NONATOMIC_FORCEOFF   \ingroup util_atomic     This is a possible parameter for NONATOMIC_BLOCK. When used, it   will cause the NONATOMIC_BLOCK to force the state of the SREG   register on exit, disabling the Global Interrupt Status flag   bit. This saves on flash space as the previous value of the SREG   register does not need to be saved at the start of the block.     Care should be taken that NONATOMIC_FORCEOFF is only used when it   is known that interrupts are disabled before the block's execution   or when the side effects of disabling global interrupts at the   block's completion are known and understood.  */  #if defined(__DOXYGEN__)  #define NONATOMIC_FORCEOFF  #else  #define NONATOMIC_FORCEOFF uint8_t sreg_save \   __attribute__((__cleanup__(__iCliParam))) = 0  #endif /* __DOXYGEN__ */  #endif