avr-libc-1.7.1/include/avr/interrupt.h - toolchain/avr-libc - Gitiles

 /* Copyright (c) 2002,2005,2007 Marek Michalkiewicz
    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: interrupt.h 2158 2010-06-10 15:48:28Z joerg_wunsch $ */

 #ifndef _AVR_INTERRUPT_H_
 #define _AVR_INTERRUPT_H_

 #include <avr/io.h>

 #if !defined(__DOXYGEN__) && !defined(__STRINGIFY)
 /* Auxiliary macro for ISR_ALIAS(). */
 #define __STRINGIFY(x) #x
 #endif /* !defined(__DOXYGEN__) */

 /**
 \file
 \@{
 */


 /** \name Global manipulation of the interrupt flag

     The global interrupt flag is maintained in the I bit of the status
     register (SREG).

     Handling interrupts frequently requires attention regarding atomic
     access to objects that could be altered by code running within an
     interrupt context, see <util/atomic.h>.

     Frequently, interrupts are being disabled for periods of time in
     order to perform certain operations without being disturbed; see
     \ref optim_code_reorder for things to be taken into account with
     respect to compiler optimizations.
 */

 #if defined(__DOXYGEN__)
 /** \def sei()
     \ingroup avr_interrupts

     \code #include <avr/interrupt.h> \endcode

     Enables interrupts by setting the global interrupt mask. This function
     actually compiles into a single line of assembly, so there is no function
     call overhead.  However, the macro also implies a <i>memory barrier</i>
     which can cause additional loss of optimization.

     In order to implement atomic access to multi-byte objects,
     consider using the macros from <util/atomic.h>, rather than
     implementing them manually with cli() and sei().
 */
 #define sei()
 #else  /* !DOXYGEN */
 # define sei()  __asm__ __volatile__ ("sei" ::: "memory")
 #endif /* DOXYGEN */

 #if defined(__DOXYGEN__)
 /** \def cli()
     \ingroup avr_interrupts

     \code #include <avr/interrupt.h> \endcode

     Disables all interrupts by clearing the global interrupt mask. This function
     actually compiles into a single line of assembly, so there is no function
     call overhead.  However, the macro also implies a <i>memory barrier</i>
     which can cause additional loss of optimization.

     In order to implement atomic access to multi-byte objects,
     consider using the macros from <util/atomic.h>, rather than
     implementing them manually with cli() and sei().
 */
 #define cli()
 #else  /* !DOXYGEN */
 # define cli()  __asm__ __volatile__ ("cli" ::: "memory")
 #endif /* DOXYGEN */


 /** \name Macros for writing interrupt handler functions */


 #if defined(__DOXYGEN__)
 /** \def ISR(vector [, attributes])
     \ingroup avr_interrupts

     \code #include <avr/interrupt.h> \endcode

     Introduces an interrupt handler function (interrupt service
     routine) that runs with global interrupts initially disabled
     by default with no attributes specified.

     The attributes are optional and alter the behaviour and resultant
     generated code of the interrupt routine. Multiple attributes may
     be used for a single function, with a space seperating each
     attribute.

     Valid attributes are ISR_BLOCK, ISR_NOBLOCK, ISR_NAKED and
     ISR_ALIASOF(vect).

     \c vector must be one of the interrupt vector names that are
     valid for the particular MCU type.
 */
 #  define ISR(vector, [attributes])
 #else  /* real code */

 #if (__GNUC__ == 4 && __GNUC_MINOR__ >= 1) || (__GNUC__ > 4)
 #  define __INTR_ATTRS used, externally_visible
 #else /* GCC < 4.1 */
 #  define __INTR_ATTRS used
 #endif

 #ifdef __cplusplus
 #  define ISR(vector, ...)            \
     extern "C" void vector (void) __attribute__ ((signal,__INTR_ATTRS)) __VA_ARGS__; \
     void vector (void)
 #else
 #  define ISR(vector, ...)            \
     void vector (void) __attribute__ ((signal,__INTR_ATTRS)) __VA_ARGS__; \
     void vector (void)
 #endif

 #endif /* DOXYGEN */

 #if defined(__DOXYGEN__)
 /** \def SIGNAL(vector)
     \ingroup avr_interrupts

     \code #include <avr/interrupt.h> \endcode

     Introduces an interrupt handler function that runs with global interrupts
     initially disabled.

     This is the same as the ISR macro without optional attributes.
     \deprecated Do not use SIGNAL() in new code. Use ISR() instead.
 */
 #  define SIGNAL(vector)
 #else  /* real code */

 #ifdef __cplusplus
 #  define SIGNAL(vector)					\
     extern "C" void vector(void) __attribute__ ((signal, __INTR_ATTRS));	\
     void vector (void)
 #else
 #  define SIGNAL(vector)					\
     void vector (void) __attribute__ ((signal, __INTR_ATTRS));		\
     void vector (void)
 #endif

 #endif /* DOXYGEN */

 #if defined(__DOXYGEN__)
 /** \def EMPTY_INTERRUPT(vector)
     \ingroup avr_interrupts

     \code #include <avr/interrupt.h> \endcode

     Defines an empty interrupt handler function. This will not generate
     any prolog or epilog code and will only return from the ISR. Do not
     define a function body as this will define it for you.
     Example:
     \code EMPTY_INTERRUPT(ADC_vect);\endcode */
 #  define EMPTY_INTERRUPT(vector)
 #else  /* real code */

 #ifdef __cplusplus
 #  define EMPTY_INTERRUPT(vector)                \
     extern "C" void vector(void) __attribute__ ((signal,naked,__INTR_ATTRS));    \
     void vector (void) {  __asm__ __volatile__ ("reti" ::); }
 #else
 #  define EMPTY_INTERRUPT(vector)                \
     void vector (void) __attribute__ ((signal,naked,__INTR_ATTRS));    \
     void vector (void) { __asm__ __volatile__ ("reti" ::); }
 #endif

 #endif /* DOXYGEN */

 #if defined(__DOXYGEN__)
 /** \def ISR_ALIAS(vector, target_vector)
     \ingroup avr_interrupts

     \code #include <avr/interrupt.h> \endcode

     Aliases a given vector to another one in the same manner as the
     ISR_ALIASOF attribute for the ISR() macro. Unlike the ISR_ALIASOF
     attribute macro however, this is compatible for all versions of
     GCC rather than just GCC version 4.2 onwards.

     \note This macro creates a trampoline function for the aliased
     macro.  This will result in a two cycle penalty for the aliased
     vector compared to the ISR the vector is aliased to, due to the
     JMP/RJMP opcode used.

     \deprecated
     For new code, the use of ISR(..., ISR_ALIASOF(...))  is
     recommended.

     Example:
     \code
     ISR(INT0_vect)
     {
         PORTB = 42;
     }

     ISR_ALIAS(INT1_vect, INT0_vect);
     \endcode
 */
 #  define ISR_ALIAS(vector, target_vector)
 #else /* real code */

 #ifdef __cplusplus
 #  if defined(__AVR_MEGA__) && __AVR_MEGA__
 #    define ISR_ALIAS(vector, tgt) extern "C" void vector (void) \
 	__attribute__((signal, naked, __INTR_ATTRS)); \
 	void vector (void) { asm volatile ("jmp " __STRINGIFY(tgt) ::); }
 #  else /* !__AVR_MEGA */
 #    define ISR_ALIAS(vector, tgt) extern "C" void vector (void) \
 	__attribute__((signal, naked, __INTR_ATTRS)); \
 	void vector (void) { asm volatile ("rjmp " __STRINGIFY(tgt) ::); }
 #  endif  /* __AVR_MEGA__ */
 #else	  /* !__cplusplus */
 #  if defined(__AVR_MEGA__) && __AVR_MEGA__
 #  define ISR_ALIAS(vector, tgt) void vector (void) \
 	__attribute__((signal, naked, __INTR_ATTRS)); \
 	void vector (void) { asm volatile ("jmp " __STRINGIFY(tgt) ::); }
 #  else /* !__AVR_MEGA */
 #  define ISR_ALIAS(vector, tgt) void vector (void) \
 	__attribute__((signal, naked, __INTR_ATTRS)); \
 	void vector (void) { asm volatile ("rjmp " __STRINGIFY(tgt) ::); }
 #  endif  /* __AVR_MEGA__ */
 #endif	/* __cplusplus */

 #endif /* DOXYGEN */

 #if defined(__DOXYGEN__)
 /** \def reti()
     \ingroup avr_interrupts

     \code #include <avr/interrupt.h> \endcode

     Returns from an interrupt routine, enabling global interrupts. This should
     be the last command executed before leaving an ISR defined with the ISR_NAKED
     attribute.

     This macro actually compiles into a single line of assembly, so there is
     no function call overhead.
 */
 #  define reti()
 #else  /* !DOXYGEN */
 #  define reti()  __asm__ __volatile__ ("reti" ::)
 #endif /* DOXYGEN */

 #if defined(__DOXYGEN__)
 /** \def BADISR_vect
     \ingroup avr_interrupts

     \code #include <avr/interrupt.h> \endcode

     This is a vector which is aliased to __vector_default, the vector
     executed when an ISR fires with no accompanying ISR handler. This
     may be used along with the ISR() macro to create a catch-all for
     undefined but used ISRs for debugging purposes.
 */
 #  define BADISR_vect
 #else  /* !DOXYGEN */
 #  define BADISR_vect __vector_default
 #endif /* DOXYGEN */

 /** \name ISR attributes */

 #if defined(__DOXYGEN__)
 /** \def ISR_BLOCK
     \ingroup avr_interrupts

     \code# include <avr/interrupt.h> \endcode

     Identical to an ISR with no attributes specified. Global
     interrupts are initially disabled by the AVR hardware when
     entering the ISR, without the compiler modifying this state.

     Use this attribute in the attributes parameter of the ISR macro.
 */
 #  define ISR_BLOCK

 /** \def ISR_NOBLOCK
     \ingroup avr_interrupts

     \code# include <avr/interrupt.h> \endcode

     ISR runs with global interrupts initially enabled.  The interrupt
     enable flag is activated by the compiler as early as possible
     within the ISR to ensure minimal processing delay for nested
     interrupts.

     This may be used to create nested ISRs, however care should be
     taken to avoid stack overflows, or to avoid infinitely entering
     the ISR for those cases where the AVR hardware does not clear the
     respective interrupt flag before entering the ISR.

     Use this attribute in the attributes parameter of the ISR macro.
 */
 #  define ISR_NOBLOCK

 /** \def ISR_NAKED
     \ingroup avr_interrupts

     \code# include <avr/interrupt.h> \endcode

     ISR is created with no prologue or epilogue code. The user code is
     responsible for preservation of the machine state including the
     SREG register, as well as placing a reti() at the end of the
     interrupt routine.

     Use this attribute in the attributes parameter of the ISR macro.
 */
 #  define ISR_NAKED

 /** \def ISR_ALIASOF(target_vector)
     \ingroup avr_interrupts

     \code#include <avr/interrupt.h>\endcode

     The ISR is linked to another ISR, specified by the vect parameter.
     This is compatible with GCC 4.2 and greater only.

     Use this attribute in the attributes parameter of the ISR macro.
 */
 #  define ISR_ALIASOF(target_vector)
 #else  /* !DOXYGEN */
 #  define ISR_BLOCK
 #  define ISR_NOBLOCK    __attribute__((interrupt))
 #  define ISR_NAKED      __attribute__((naked))
 #  define ISR_ALIASOF(v) __attribute__((alias(__STRINGIFY(v))))
 #endif /* DOXYGEN */

 /* \@} */

 #endif
	/* Copyright (c) 2002,2005,2007 Marek Michalkiewicz
	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: interrupt.h 2158 2010-06-10 15:48:28Z joerg_wunsch $ */

	#ifndef _AVR_INTERRUPT_H_
	#define _AVR_INTERRUPT_H_

	#include <avr/io.h>

	#if !defined(__DOXYGEN__) && !defined(__STRINGIFY)
	/* Auxiliary macro for ISR_ALIAS(). */
	#define __STRINGIFY(x) #x
	#endif /* !defined(__DOXYGEN__) */

	/**
	\file
	\@{
	*/


	/** \name Global manipulation of the interrupt flag

	The global interrupt flag is maintained in the I bit of the status
	register (SREG).

	Handling interrupts frequently requires attention regarding atomic
	access to objects that could be altered by code running within an
	interrupt context, see <util/atomic.h>.

	Frequently, interrupts are being disabled for periods of time in
	order to perform certain operations without being disturbed; see
	\ref optim_code_reorder for things to be taken into account with
	respect to compiler optimizations.
	*/

	#if defined(__DOXYGEN__)
	/** \def sei()
	\ingroup avr_interrupts

	\code #include <avr/interrupt.h> \endcode

	Enables interrupts by setting the global interrupt mask. This function
	actually compiles into a single line of assembly, so there is no function
	call overhead. However, the macro also implies a <i>memory barrier</i>
	which can cause additional loss of optimization.

	In order to implement atomic access to multi-byte objects,
	consider using the macros from <util/atomic.h>, rather than
	implementing them manually with cli() and sei().
	*/
	#define sei()
	#else /* !DOXYGEN */
	# define sei() __asm__ __volatile__ ("sei" ::: "memory")
	#endif /* DOXYGEN */

	#if defined(__DOXYGEN__)
	/** \def cli()
	\ingroup avr_interrupts

	\code #include <avr/interrupt.h> \endcode

	Disables all interrupts by clearing the global interrupt mask. This function
	actually compiles into a single line of assembly, so there is no function
	call overhead. However, the macro also implies a <i>memory barrier</i>
	which can cause additional loss of optimization.

	In order to implement atomic access to multi-byte objects,
	consider using the macros from <util/atomic.h>, rather than
	implementing them manually with cli() and sei().
	*/
	#define cli()
	#else /* !DOXYGEN */
	# define cli() __asm__ __volatile__ ("cli" ::: "memory")
	#endif /* DOXYGEN */


	/** \name Macros for writing interrupt handler functions */


	#if defined(__DOXYGEN__)
	/** \def ISR(vector [, attributes])
	\ingroup avr_interrupts

	\code #include <avr/interrupt.h> \endcode

	Introduces an interrupt handler function (interrupt service
	routine) that runs with global interrupts initially disabled
	by default with no attributes specified.

	The attributes are optional and alter the behaviour and resultant
	generated code of the interrupt routine. Multiple attributes may
	be used for a single function, with a space seperating each
	attribute.

	Valid attributes are ISR_BLOCK, ISR_NOBLOCK, ISR_NAKED and
	ISR_ALIASOF(vect).

	\c vector must be one of the interrupt vector names that are
	valid for the particular MCU type.
	*/
	# define ISR(vector, [attributes])
	#else /* real code */

	#if (__GNUC__ == 4 && __GNUC_MINOR__ >= 1) \|\| (__GNUC__ > 4)
	# define __INTR_ATTRS used, externally_visible
	#else /* GCC < 4.1 */
	# define __INTR_ATTRS used
	#endif

	#ifdef __cplusplus
	# define ISR(vector, ...) \
	extern "C" void vector (void) __attribute__ ((signal,__INTR_ATTRS)) __VA_ARGS__; \
	void vector (void)
	#else
	# define ISR(vector, ...) \
	void vector (void) __attribute__ ((signal,__INTR_ATTRS)) __VA_ARGS__; \
	void vector (void)
	#endif

	#endif /* DOXYGEN */

	#if defined(__DOXYGEN__)
	/** \def SIGNAL(vector)
	\ingroup avr_interrupts

	\code #include <avr/interrupt.h> \endcode

	Introduces an interrupt handler function that runs with global interrupts
	initially disabled.

	This is the same as the ISR macro without optional attributes.
	\deprecated Do not use SIGNAL() in new code. Use ISR() instead.
	*/
	# define SIGNAL(vector)
	#else /* real code */

	#ifdef __cplusplus
	# define SIGNAL(vector) \
	extern "C" void vector(void) __attribute__ ((signal, __INTR_ATTRS)); \
	void vector (void)
	#else
	# define SIGNAL(vector) \
	void vector (void) __attribute__ ((signal, __INTR_ATTRS)); \
	void vector (void)
	#endif

	#endif /* DOXYGEN */

	#if defined(__DOXYGEN__)
	/** \def EMPTY_INTERRUPT(vector)
	\ingroup avr_interrupts

	\code #include <avr/interrupt.h> \endcode

	Defines an empty interrupt handler function. This will not generate
	any prolog or epilog code and will only return from the ISR. Do not
	define a function body as this will define it for you.
	Example:
	\code EMPTY_INTERRUPT(ADC_vect);\endcode */
	# define EMPTY_INTERRUPT(vector)
	#else /* real code */

	#ifdef __cplusplus
	# define EMPTY_INTERRUPT(vector) \
	extern "C" void vector(void) __attribute__ ((signal,naked,__INTR_ATTRS)); \
	void vector (void) { __asm__ __volatile__ ("reti" ::); }
	#else
	# define EMPTY_INTERRUPT(vector) \
	void vector (void) __attribute__ ((signal,naked,__INTR_ATTRS)); \
	void vector (void) { __asm__ __volatile__ ("reti" ::); }
	#endif

	#endif /* DOXYGEN */

	#if defined(__DOXYGEN__)
	/** \def ISR_ALIAS(vector, target_vector)
	\ingroup avr_interrupts

	\code #include <avr/interrupt.h> \endcode

	Aliases a given vector to another one in the same manner as the
	ISR_ALIASOF attribute for the ISR() macro. Unlike the ISR_ALIASOF
	attribute macro however, this is compatible for all versions of
	GCC rather than just GCC version 4.2 onwards.

	\note This macro creates a trampoline function for the aliased
	macro. This will result in a two cycle penalty for the aliased
	vector compared to the ISR the vector is aliased to, due to the
	JMP/RJMP opcode used.

	\deprecated
	For new code, the use of ISR(..., ISR_ALIASOF(...)) is
	recommended.

	Example:
	\code
	ISR(INT0_vect)
	{
	PORTB = 42;
	}

	ISR_ALIAS(INT1_vect, INT0_vect);
	\endcode
	*/
	# define ISR_ALIAS(vector, target_vector)
	#else /* real code */

	#ifdef __cplusplus
	# if defined(__AVR_MEGA__) && __AVR_MEGA__
	# define ISR_ALIAS(vector, tgt) extern "C" void vector (void) \
	__attribute__((signal, naked, __INTR_ATTRS)); \
	void vector (void) { asm volatile ("jmp " __STRINGIFY(tgt) ::); }
	# else /* !__AVR_MEGA */
	# define ISR_ALIAS(vector, tgt) extern "C" void vector (void) \
	__attribute__((signal, naked, __INTR_ATTRS)); \
	void vector (void) { asm volatile ("rjmp " __STRINGIFY(tgt) ::); }
	# endif /* __AVR_MEGA__ */
	#else /* !__cplusplus */
	# if defined(__AVR_MEGA__) && __AVR_MEGA__
	# define ISR_ALIAS(vector, tgt) void vector (void) \
	__attribute__((signal, naked, __INTR_ATTRS)); \
	void vector (void) { asm volatile ("jmp " __STRINGIFY(tgt) ::); }
	# else /* !__AVR_MEGA */
	# define ISR_ALIAS(vector, tgt) void vector (void) \
	__attribute__((signal, naked, __INTR_ATTRS)); \
	void vector (void) { asm volatile ("rjmp " __STRINGIFY(tgt) ::); }
	# endif /* __AVR_MEGA__ */
	#endif /* __cplusplus */

	#endif /* DOXYGEN */

	#if defined(__DOXYGEN__)
	/** \def reti()
	\ingroup avr_interrupts

	\code #include <avr/interrupt.h> \endcode

	Returns from an interrupt routine, enabling global interrupts. This should
	be the last command executed before leaving an ISR defined with the ISR_NAKED
	attribute.

	This macro actually compiles into a single line of assembly, so there is
	no function call overhead.
	*/
	# define reti()
	#else /* !DOXYGEN */
	# define reti() __asm__ __volatile__ ("reti" ::)
	#endif /* DOXYGEN */

	#if defined(__DOXYGEN__)
	/** \def BADISR_vect
	\ingroup avr_interrupts

	\code #include <avr/interrupt.h> \endcode

	This is a vector which is aliased to __vector_default, the vector
	executed when an ISR fires with no accompanying ISR handler. This
	may be used along with the ISR() macro to create a catch-all for
	undefined but used ISRs for debugging purposes.
	*/
	# define BADISR_vect
	#else /* !DOXYGEN */
	# define BADISR_vect __vector_default
	#endif /* DOXYGEN */

	/** \name ISR attributes */

	#if defined(__DOXYGEN__)
	/** \def ISR_BLOCK
	\ingroup avr_interrupts

	\code# include <avr/interrupt.h> \endcode

	Identical to an ISR with no attributes specified. Global
	interrupts are initially disabled by the AVR hardware when
	entering the ISR, without the compiler modifying this state.

	Use this attribute in the attributes parameter of the ISR macro.
	*/
	# define ISR_BLOCK

	/** \def ISR_NOBLOCK
	\ingroup avr_interrupts

	\code# include <avr/interrupt.h> \endcode

	ISR runs with global interrupts initially enabled. The interrupt
	enable flag is activated by the compiler as early as possible
	within the ISR to ensure minimal processing delay for nested
	interrupts.

	This may be used to create nested ISRs, however care should be
	taken to avoid stack overflows, or to avoid infinitely entering
	the ISR for those cases where the AVR hardware does not clear the
	respective interrupt flag before entering the ISR.

	Use this attribute in the attributes parameter of the ISR macro.
	*/
	# define ISR_NOBLOCK

	/** \def ISR_NAKED
	\ingroup avr_interrupts

	\code# include <avr/interrupt.h> \endcode

	ISR is created with no prologue or epilogue code. The user code is
	responsible for preservation of the machine state including the
	SREG register, as well as placing a reti() at the end of the
	interrupt routine.

	Use this attribute in the attributes parameter of the ISR macro.
	*/
	# define ISR_NAKED

	/** \def ISR_ALIASOF(target_vector)
	\ingroup avr_interrupts

	\code#include <avr/interrupt.h>\endcode

	The ISR is linked to another ISR, specified by the vect parameter.
	This is compatible with GCC 4.2 and greater only.

	Use this attribute in the attributes parameter of the ISR macro.
	*/
	# define ISR_ALIASOF(target_vector)
	#else /* !DOXYGEN */
	# define ISR_BLOCK
	# define ISR_NOBLOCK __attribute__((interrupt))
	# define ISR_NAKED __attribute__((naked))
	# define ISR_ALIASOF(v) __attribute__((alias(__STRINGIFY(v))))
	#endif /* DOXYGEN */

	/* \@} */

	#endif