FreeRTOS CortexM3 M4中断优先级设置总结

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);
参考博文
FreeRTOS STM32移植笔记
FreeRTOS学习笔记——任务间使用队列同步数据
FreeRTOS学习笔记——二值型信号量
FreeRTOS学习笔记——互斥型信号量
如何在FreeRTOS下实现低功耗——MSP430F5438平台

参考资料
【1】 http://www.freertos.org/RTOS-Cortex-M3-M4.html


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