[stm32]中断优先级设置

1. 设置优先级组NVIC_PriorityGroupConfig
2. 设置中断源的抢占优先级(pre-emption priority)和响应优先级(sub-priority)，然后使能
3. 初始化NVIC_Init(&NVIC_InitStructure)

void NVIC_Config(void)
{
   NVIC_InitTypeDef NVIC_InitStructure;
   /* Configure the NVIC Preemption Priority Bits */
   NVIC_PriorityGroupConfig(NVIC_PriorityGroup_0);
   /* Enable the USARTy Interrupt */
   NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
   NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
   NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
   NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
   NVIC_Init(&NVIC_InitStructure);
   //
   NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel4_IRQn;
   NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
   NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
   NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
   NVIC_Init(&NVIC_InitStructure);
}

NOTE

1. NVIC_PriorityGroupConfig可设置多次，但以最后一次为准

2. 设定的中断源优先级不能超过优先级组设置的范围，否则结果不可知

3. 抢占式优先级别相同的中断源之间没有嵌套关系

4. 当两个中断源的抢占式优先级相同时，这两个中断将没有嵌套关系

5. 抢占式优先级或响应优先级相同时，根据他们在中断表中的排位顺序决定先处理哪一个