stm32 设置systick中断抢先式优先级


链接地址：http://blog.csdn.net/sunjiajiang/article/details/7741715

最近使用STM32时希望将systick的中断优先级降低，但是CMSIS里给出的例子都是类似

    NVIC_InitStructure.NVIC_IRQChannel = TIM1_UP_IRQn;  
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;  
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;  
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;  
    NVIC_Init(&NVIC_InitStructure);  

<span style="font-size:14px;"><span style="font-family:KaiTi_GB2312;font-size:18px;">    NVIC_InitStructure.NVIC_IRQChannel = TIM1_UP_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);</span></span>

还是没有配置systick。

后来阅读CM3的技术参考手册，讲解了NVIC的配置。

中断分为内核中断和芯片的中断，配置的寄存器位置不同。芯片的中断配置在NVIC的IP内，内核的中断配置在SCB内。

可以直接调用core_cm3.h里的函数

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  */  
}  

<span style="font-size:14px;"><span style="font-family:KaiTi_GB2312;font-size:18px;">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  */
}</span></span>

这个函数实现了两类中断优先级的配置。

但是直观上来看看不到抢先式优先级与子优先级。

首先，配置优先级组，可以使用固件库的程序，也可以用core_cm3.h的函数。

void NVIC_PriorityGroupConfig(uint32_t NVIC_PriorityGroup)  
{  
  /* Set the PRIGROUP[10:8] bits according to NVIC_PriorityGroup value */  
  SCB->AIRCR = AIRCR_VECTKEY_MASK | NVIC_PriorityGroup;  
}  

<span style="font-size:14px;"><span style="font-family:KaiTi_GB2312;font-size:18px;">void NVIC_PriorityGroupConfig(uint32_t NVIC_PriorityGroup)
{
/* Set the PRIGROUP[10:8] bits according to NVIC_PriorityGroup value */
SCB->AIRCR = AIRCR_VECTKEY_MASK | NVIC_PriorityGroup;
}</span></span>

或

static __INLINE void NVIC_SetPriorityGrouping(uint32_t PriorityGroup)  
{  
  uint32_t reg_value;  
  uint32_t PriorityGroupTmp = (PriorityGroup & 0x07);                         /* only values 0..7 are used          */  
    
  reg_value  =  SCB->AIRCR;                                                   /* read old register configuration    */  
  reg_value &= ~(SCB_AIRCR_VECTKEY_Msk | SCB_AIRCR_PRIGROUP_Msk);             /* clear bits to change               */  
  reg_value  =  (reg_value                       |  
                (0x5FA << SCB_AIRCR_VECTKEY_Pos) |   
                (PriorityGroupTmp << 8));                                     /* Insert write key and priorty group */  
  SCB->AIRCR =  reg_value;  
}  

<span style="font-size:14px;"><span style="font-family:KaiTi_GB2312;font-size:18px;">static __INLINE void NVIC_SetPriorityGrouping(uint32_t PriorityGroup)
{
uint32_t reg_value;
uint32_t PriorityGroupTmp = (PriorityGroup & 0x07);                         /* only values 0..7 are used          */

reg_value  =  SCB->AIRCR;                                                   /* read old register configuration    */
reg_value &= ~(SCB_AIRCR_VECTKEY_Msk | SCB_AIRCR_PRIGROUP_Msk);             /* clear bits to change               */
reg_value  =  (reg_value                       |
(0x5FA << SCB_AIRCR_VECTKEY_Pos) |
(PriorityGroupTmp << 8));                                     /* Insert write key and priorty group */
SCB->AIRCR =  reg_value;
}</span></span>

参数范围为0～7，具体如下



随后配置各个中断的优先级，对于外设的中断可以使用固件库的程序，比较直观。如最前面所给出的例子，但是根据其实现，是不能够用来配置内核中断的，例如

NVIC_InitStructure.NVIC_IRQChannel = SysTick_IRQn;  
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;  
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;  
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;  
NVIC_Init(&NVIC_InitStructure);  

<span style="font-size:14px;"><span style="font-family:KaiTi_GB2312;font-size:18px;">    NVIC_InitStructure.NVIC_IRQChannel = SysTick_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);</span></span>

这是错误的，因为内部使用IRQn寻址，而SysTick_IRQn为-1.

所以对于Sysick使用core_cm3.h的函数

NVIC_SetPriority(SysTick_IRQn, 4);  

<span style="font-size:14px;"><span style="font-family:KaiTi_GB2312;font-size:18px;">NVIC_SetPriority(SysTick_IRQn, 4);</span></span>

这时不能显式的看出抢先式优先级与子优先级，写入的优先级需要根据优先级组的配置来选择。

NVIC_SetPriority(SysTick_IRQn, n);  
n=0x00~0x03 设置Systick为抢占优先级0  
n=0x04~0x07 设置Systick为抢占优先级1  
n=0x08~0x0B 设置Systick为抢占优先级2  
n=0x0C~0x0F 设置Systick为抢占优先级3    

<span style="font-size:14px;"><span style="font-family:KaiTi_GB2312;font-size:18px;">NVIC_SetPriority(SysTick_IRQn, n);
n=0x00~0x03 设置Systick为抢占优先级0
n=0x04~0x07 设置Systick为抢占优先级1
n=0x08~0x0B 设置Systick为抢占优先级2
n=0x0C~0x0F 设置Systick为抢占优先级3  </span></span>

NVIC_SetPriority函数指定中断优先级的寄存器位（STM32只用4位来表示优先级）的数据，例如中断优先级组设置为了2，即高2位用于指定抢占式优先级，低2位用于指定响应优先级，0x00~0x03高2位为0，所以抢占优先级为0；0x04~0x07高2位为1，所以抢占优先级为1，以此类推。