[FreeRTOS].FreeRTOS CortexM3 M4中断优先级设置总结

转自：https://blog.csdn.net/xukai871105/article/details/53516857

前言
本文将说明在FreeRTOS嵌入式操作系统中，如何设置STM32 Cortex M3和M4系列MCU的中断优先级。
总结

• 【1】STM32L1系列，STM32F1系列，STM32F4系列，设置NVIC时需要使用NVIC_PriorityGroup_4。
• 【2】抢占优先级的要比“MAX”更大，而比“LOWEST”更小。例如 configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY=5 ， configLIBRARY_LOWEST_INTERRUPT_PRIORITY=15 ，那么NVIC抢占优先级设置的具体值应该比MAX=5更大（包括等于），比LOWEST=15更小（包括等于），也就是说5，6，7，8，9，10，11，12，13，14，15肯定是合法值。
• 【3】FreeRTOS中，数值越大优先级越高，这种优先级可以成为逻辑优先级。Cortex M3/M4中断中，数值越大优先级越低，这种优先级成为中断优先级。两者相反，所以才会出现比"MAX"更大而比“LOWEST”更小的情况。

示意代码
【FreeRTOSConfig.h】

/* Use the system definition, if there is one */
#ifdef __NVIC_PRIO_BITS
#define configPRIO_BITS __NVIC_PRIO_BITS
#else
#define configPRIO_BITS 4 /* 15 priority levels */
#endif

#define configLIBRARY_LOWEST_INTERRUPT_PRIORITY    15
#define configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY    5
/* The lowest priority. */
#define configKERNEL_INTERRUPT_PRIORITY ( configLIBRARY_LOWEST_INTERRUPT_PRIORITY << (8 - configPRIO_BITS) )
/* Priority 5, or 95 as only the top four bits are implemented. */
/* !!!! configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to zero !!!!
See http://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html. */
#define configMAX_SYSCALL_INTERRUPT_PRIORITY ( configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY << (8 - configPRIO_BITS) )

【NVIC设置】
【示例A】

NVIC_InitTypeDef NVIC_InitStructure;
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_4);

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

【示例A】

NVIC_InitTypeDef NVIC_InitStructure;
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_4);

NVIC_InitStructure.NVIC_IRQChannel = XXXX_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = configLIBRARY_LOWEST_INTERRUPT_PRIORITY-1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);