Change from: https://blog.csdn.net/xukai871105/article/details/53516857

Preface
This article will show how to set the interrupt priority of STM32 Cortex M3 and M4 Series MCU in FreeRTOS embedded operating system.
summary

• [1] STM32L1 series, STM32F1 series and STM32F4 series. NVIC? Prioritygroup? 4 is required when setting NVIC.
• [2] the priority of preemption is larger than "MAX" and smaller than "low". For example, if "configlibrary" MAX "syscall" interrupt "priority = 5," configlibrary "low" interrupt "priority = 15", then the specific value of NVIC preemption priority setting should be larger (including equal) than MAX=5, and smaller (including equal) than low = 15, that is to say, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 must be legal.
• [3] in FreeRTOS, the higher the value is, the higher the priority is. This priority can be a logical priority. In Cortex M3/M4 interrupt, the higher the value, the lower the priority, which becomes the interrupt priority. On the contrary, they are bigger than "MAX" and smaller than "lost".

Schematic code
[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 settings]
[example 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);

[example 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);