FreeRTOS interrupt settings based on STM32 applications-EEWORLD

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1. Introduction to FreeRTOS interrupt settings

Two macros are defined in FreeRTOSConfig.h:

configKERNEL_INTERRUPT_PRIORITY
configMAX_SYSCALL_INTERRUPT_PRIORITY
configKERNEL_INTERRUPT_PRIORITY is used to set the interrupt priority of the RTOS kernel. Because the RTOS kernel interrupt is not allowed to preempt the interrupt used by the user, this macro is generally defined as the lowest hardware priority.
configMAX_SYSCALL_INTERRUPT_PRIORITY is used to set the highest interrupt priority that can safely call FreeRTOS API functions in the interrupt service routine. When the priority is less than or equal to the priority represented by this macro, the program can safely call FreeRTOS API functions in the interrupt service routine; if the priority is greater than the priority represented by this macro, it means that FreeRTOS cannot disable this interrupt, and no API function can be called in this interrupt service routine.

That is, the RTOS interrupt nesting scheme divides the available interrupt priorities into two groups: those that will be overwritten by the RTOS critical section and those that will never be overwritten so these are always enabled. The configMAX_SYSCALL_INTERRUPT_PRIORITY setting is the boundary value between these two groups.

As shown in the figure above, when using FreeRTOS in STM32, the system defaults to:

//This is the raw value as per the Cortex-M3 NVIC. Values can be 255
(lowest) to 0 (1?) (highest).
#define configKERNEL_INTERRUPT_PRIORITY 255 (0xFF is priority 15)
//!!!! 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 191 (0xBF is priority 11)

Therefore, interrupts with priority levels of 0 to 10 will not be delayed by the kernel and can be nested but cannot call API functions. Interrupts between 11 and 15 can call API functions ending with FromISR.

Keywords：STM32 Reference address：FreeRTOS interrupt settings based on STM32 applications

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