(*(void(*)())x)(), 函数指针

系统启动时硬件将调用首地址为x位置的子例程, 实现语句如下: //4.7.3, P103

(*(void(*)())x)(); 从内向外分析如下:

1. void(*)(): 函数指针类型, 参数和返回值都为空

2. (void(*)())x: 将x强制转换为函数指针类型. x为地址, 即一个函数存在首地址为x的一段区域内

3. (*(void(*)())x): 前面加*, 指针取值, 取x地址开始的一段内容, 即对函数的引用

4. (*(void(*)())x)(): 最后加上(), 函数调用, 你懂的

利用 typedef 更好理解:

typedef void (*pFunction)(void); //定义函数指针类型(函数前带*)

(*(pFunction)x)();

//PC指针指到0x2c处的SVC_Handler函数入口地址，也就是UpdateHandler, 0x2c不就是SVCall handler

(*((void (*)(void))(*(unsigned long *)0x2c)))();

Luminary提供的 interrupt.c 中如下:

// The processor vector table.

#if defined(ewarm)

static __no_init void (*g_pfnRAMVectors[NUM_INTERRUPTS])(void) @ "VTABLE";

#elif defined(sourcerygxx)

static __attribute__((section(".cs3.region-head.ram")))

void (*g_pfnRAMVectors[NUM_INTERRUPTS])(void);

#elif defined(ccs)

#pragma DATA_SECTION(g_pfnRAMVectors, ".vtable")

void (*g_pfnRAMVectors[NUM_INTERRUPTS])(void);

#else

static __attribute__((section("vtable")))

void (*g_pfnRAMVectors[NUM_INTERRUPTS])(void);

#endif

void IntRegister(unsigned long ulInterrupt, void (*pfnHandler)(void))

{

  unsigned long ulIdx, ulValue;

  // Check the arguments.

  ASSERT(ulInterrupt < NUM_INTERRUPTS);

  // Make sure that the RAM vector table is correctly aligned.

  ASSERT(((unsigned long)g_pfnRAMVectors & 0x000003ff) == 0);

  // See if the RAM vector table has been initialized.

  if(HWREG(NVIC_VTABLE) != (unsigned long)g_pfnRAMVectors)

  {

      // Copy the vector table from the beginning of FLASH to the RAM vector table.

      ulValue = HWREG(NVIC_VTABLE);

      for(ulIdx = 0; ulIdx < NUM_INTERRUPTS; ulIdx++)

      {

      g_pfnRAMVectors[ulIdx] = (void (*)(void))HWREG((ulIdx * 4) + ulValue);

      }

      // Point NVIC at the RAM vector table.

      HWREG(NVIC_VTABLE) = (unsigned long)g_pfnRAMVectors;

  }

  // Save the interrupt handler.

  g_pfnRAMVectors[ulInterrupt] = pfnHandler;

}

static void IntDefaultHandler(void)

{

    // Go into an infinite loop.

    while(1) {}

}

void IntUnregister(unsigned long ulInterrupt)

{

    // Check the arguments.

    ASSERT(ulInterrupt < NUM_INTERRUPTS);

    // Reset the interrupt handler.

    g_pfnRAMVectors[ulInterrupt] = IntDefaultHandler;

}