先占优先级与从优先级

NVIC_IRQChannelPreemptionPriority：先占优先级

NVIC_IRQChannelSubPriority：从优先级

高先占优先级中断可以打断低先占优先级的中断，即可中断嵌套。先占优先级号码越小优先级越高

当先占优先级号码相同时，从优先级号码起作用。同先占优先级下的中断是不能进行嵌套的，只能根据从优先级的号码进行排队，从优先级号码即为排队号码，号码越低越靠前。

先用函数NVIC_PriorityGroupConfig(NVIC_PriorityGroup_x)决定有几个先占优先级和从优先级。NVIC_PriorityGroup_x可取如下值。

NVIC_PriorityGroup_0 => 选择第0组
NVIC_PriorityGroup_1 => 选择第1组
NVIC_PriorityGroup_2 => 选择第2组
NVIC_PriorityGroup_3 => 选择第3组
NVIC_PriorityGroup_4 => 选择第4组

举例：

NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1)；//配置为1组。

NVIC_InitStructure.NVIC_IRQChannel = EXTI0_IRQChannel;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0; // 指定抢占式优先级别0，可取0-1

NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE；//使能中断

 NVIC_Init(&NVIC_InitStructure);

 

NVIC_InitStructure.NVIC_IRQChannel = SPI1_IRQChannel;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1; // 指定抢占式优先级别1，可取0-1

NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; // 指定从优先级别0，可取0-7

NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

NVIC_Init(&NVIC_InitStructure);

 

NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQChannel;

NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;

NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1; // 指定从优先级别1，可取0-7

NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

  NVIC_Init(&NVIC_InitStructure);

EXTI0_IRQChannel 先占优先级比SPI1_IRQChannel、USART1_IRQChannel高，所以EXTI0_IRQChannel中断可以打断正在执行的SPI1_IRQChannel/USART1_IRQChannel中断，实现中断嵌套。

SPI1_IRQChannel、USART1_IRQChannel先占优先级相等，不能相互打断，即在执行SPI1_IRQChannel/USART1_IRQChannel中断时USART1_IRQChannel/SPI1_IRQChannel中断无法打断。同时产生SPI1_IRQChannel、USART1_IRQChannel中断时，要根据从优先级进行排队，SPI1_IRQChannel从优先级比较高，所以先执行SPI1_IRQChannel中断。