原创 AVR GCC中 ISR 与 SIGNAL 的关系

在 interrupt.h中（Copyright (c) 2007）有：

#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 */

    由上可知：ISR与SIGNAL属性是基本相同的，都是不能中断嵌套。区别是ISR(vector [, attributes])参数可变,，而SIGNAL(vector)只有一个参数vector。GCC建议使用ISR，代替SIGNAL。SIGNAL 是为了相容旧程序代码而保留下来的。
    所谓不能中断嵌套，是指执行中断服务时不能再响应其他中断。因为进入中断程序后，立即会禁止总中断，而中断返回前使能总中断。要中断嵌套，须进入中断程序后使能总中断，中断返回之前禁止总中断。