中断解析

NVIC_SetPriority函数解析

/**
 * @brief  Set the priority for an interrupt
 *
 * @param  IRQn      The number of the interrupt for set priority
 * @param  priority  The priority to set
 *
 * Set the priority for the specified interrupt. The interrupt 
 * number can be positive to specify an external (device specific) 
 * interrupt, or negative to specify an internal (core) interrupt.
 *
 * Note: The priority cannot be set for every core interrupt.
 */
static __INLINE void NVIC_SetPriority(IRQn_Type IRQn, uint32_t priority)
{
  if(IRQn < 0) {
    SCB->SHP[((uint32_t)(IRQn) & 0xF)-4] = ((priority << (8 - __NVIC_PRIO_BITS)) & 0xff); } /* set Priority for Cortex-M3 System Interrupts */
  else {
    NVIC->IP[(uint32_t)(IRQn)] = ((priority << (8 - __NVIC_PRIO_BITS)) & 0xff);    }        /* set Priority for device specific Interrupts  */
}

NVIC_SetPriority函数的作用：

为中断号IRQn的中断，设置优先级。在这里分为两种情况：

1）internal interrupt，即内核里面的外设； IRQn < 0

2）external interrupt，即普通的外设；IRQn > 0

注意：

1.对Cortex-M3内核里面的一个外设，它的中断号是小于0的。systick的中断号为-1

2.在NVIC_SetPriority中，我们需要配置的是SCB->SHP寄存器。该寄存器是什么呢？

我们需要查看Cortex-M3内核的手册：

System control block(SCB)

SHP又是什么？

System Handler Priority registersx(SHPR)，当我们设置内核里面的一个外设的中断优先级时，我们就要设置该寄存器。

typedef struct
{
  __I  uint32_t CPUID;                        /*!< Offset: 0x00  CPU ID Base Register                                  */
  __IO uint32_t ICSR;                         /*!< Offset: 0x04  Interrupt Control State Register                      */
  __IO uint32_t VTOR;                         /*!< Offset: 0x08  Vector Table Offset Register                          */
  __IO uint32_t AIRCR;                        /*!< Offset: 0x0C  Application Interrupt / Reset Control Register        */
  __IO uint32_t SCR;                          /*!< Offset: 0x10  System Control Register                               */
  __IO uint32_t CCR;                          /*!< Offset: 0x14  Configuration Control Register                        */
  __IO uint8_t  SHP[12];                      /*!< Offset: 0x18  System Handlers Priority Registers (4-7, 8-11, 12-15) */
  __IO uint32_t SHCSR;                        /*!< Offset: 0x24  System Handler Control and State Register             */
  __IO uint32_t CFSR;                         /*!< Offset: 0x28  Configurable Fault Status Register                    */
  __IO uint32_t HFSR;                         /*!< Offset: 0x2C  Hard Fault Status Register                            */
  __IO uint32_t DFSR;                         /*!< Offset: 0x30  Debug Fault Status Register                           */
  __IO uint32_t MMFAR;                        /*!< Offset: 0x34  Mem Manage Address Register                           */
  __IO uint32_t BFAR;                         /*!< Offset: 0x38  Bus Fault Address Register                            */
  __IO uint32_t AFSR;                         /*!< Offset: 0x3C  Auxiliary Fault Status Register                       */
  __I  uint32_t PFR[2];                       /*!< Offset: 0x40  Processor Feature Register                            */
  __I  uint32_t DFR;                          /*!< Offset: 0x48  Debug Feature Register                                */
  __I  uint32_t ADR;                          /*!< Offset: 0x4C  Auxiliary Feature Register                            */
  __I  uint32_t MMFR[4];                      /*!< Offset: 0x50  Memory Model Feature Register                         */
  __I  uint32_t ISAR[5];                      /*!< Offset: 0x60  ISA Feature Register                                  */
} SCB_Type;