SCM learning notes 6 -- interrupt system (based on Baiwen STM32F103 series tutorials)

Chapter six interrupt

Section 1 The concept of interruption

Simply speaking , That is, he can interrupt the task currently being performed by the system , Give Way CPU Give priority to this task , When this task is over ,CPU To return to the place where I was interrupted just now and re execute the program .

Interrupts are generally divided into System exception and External interrupt . Usually , hold CPU An internal emergency is called an exception , Such as illegal instructions （ Divide by zero ）、 Address access cross-border, etc ; Put the CPU An emergency event caused by an external on-chip peripheral is called an interrupt , such as GPIO Pin level change 、 Timer overflow, etc .

In the second quarter Interrupts and priorities

2.1Cortex-M3 Interrupts and priorities

Cortex-M3 Shared kernel 0-255, common 256 A break , Which number 0_{15 It's a system exception **,**16}255 It's an external interrupt . Each interrupt has its own specific trigger condition , When their trigger conditions are met , The system will be interrupted ,CPU It will jump to the corresponding interrupt service function to execute .

The name of the system exception is determined , The manufacturer cannot modify . External interrupts can define their own interrupt function names . Priority is the status of each interrupt 、 The level of importance , The more important the interruption , The higher his priority . When several interrupts occur at the same time ,CPU Will give priority to the execution of higher priority interrupts , Interrupts with relatively low priority can only be executed after the execution of interrupts with high priority . stay Cortex-M3 The kernel The lower the priority value , The higher his priority . Details can be found 2_ Official information \10.0_Cortex-M3 Authoritative guide .

As mentioned above, when multiple interrupts occur at the same time , The system will give priority to interrupts with higher priority , So how does the system manage and judge the priority of each interrupt .
Cortex-M3 The kernel has a peripheral dedicated to managing interrupts NVIC (Nested Vectored Interrupt Controller, Nested vector interrupt controller ) It is used to control the priority of various interrupts to realize the nesting and scheduling of interrupts .
NVIC Is a total interrupt controller , Whether you come or not The exception of the kernel is also the external interrupt of the peripheral , All by NVIC Unified management .
except Reset( Reset ）、NMI(Non Maskable Interrupt, Do not mask interrupts )、HardFault（ Hardware exception 〉, Their priorities are fixed , And the priority is negative , The highest. . The remaining exceptions or interrupts , Can be modified NVIC Register adjustment priority （ but Cannot be set to a negative number , The minimum is 0）.

At the same time Cortex-M3 in , Split the priority into preemption (Preempt Priority) and Sub priority (Subpriority) , Each interrupt needs to specify these two levels .

preemption It's a decision preemption Of . This preemption is for interrupts , Interrupts with high preemption priority can CPU Grab it . If CPU Executing an interrupt function , Preempting interrupts with higher priority can interrupt running interrupts , Give Way CPU Run interrupts with higher priority .

Sub priority It determines the order of operation , He There is no preemption function , When the preemption priority of two interrupts is the same , Interrupts with higher sub priority run first , But if the interrupt with low sub priority is executing , Interrupts with high sub priority can only be executed after the execution of interrupts with low sub priority , Because the sub priority has no preemption function .

if The two priorities are the same, and the position of interrupts in the interrupt exception table , The more forward, the more responsive . For example, the number in the figure above 16 Of IRQ_0 And number 255 Of IRQ_239 At the same time , Number 16 Of IRQ_0 priority .

Through these two priorities , The system can realize Break nesting .

Both priorities pass 8 individual Bit To control . High location is the priority , Low location is sub priority .

For example, choose PRIGROUP = 4; Then preempt priority 7-5 position , common 2^3 = 8 Priority ; Sub priority accounts for 4-0 position , common 2^5 = 32 Priority .

It should be noted that , For priority grouping , in the majority of cases , Once the grouping is set , There is no need to reset this register before resetting . That is to say, priority groups should be set at the beginning of the program , Don't change in the future .

2.2STM32 Interrupts and priorities

1、 Break the introduction

STM32 Is based on Cortex-M3 Kernel , therefore STM32 The interrupt 、 Priority settings and their features and Cortex-M3 The kernel is the same , It's just STM32 Cut it . because Cortex-M3 The design has 256 Kind of interrupt , But most MCU It doesn't take so many interrupts , such as STM32F103 The series only has 70 There are exceptions and interrupts , The top 15 It's an exception （ Yes 5 Reserved ）, Back 60 One is an external interrupt .

STM32 The interruption of has not changed much , Just remove some external interrupts that can be changed , At the same time, the interrupt numbers of all interrupts are rearranged .STM32 Medium Reset and NMI It belongs to the interrupt when the system starts , So the interrupt number is not set , And then from HardFault The starting interrupt number is from -13 Start increasing up . The external interrupt number starts from 0 It's starting to increase .

2、 Priority introduction

STM32F103 Inherited Cortex-M3 Interrupt priority rule , It also uses preemptive priority and sub priority to control interrupt priority . But because STM32F103 There are many fewer interruptions , So interrupt priority can't be used that much , Use only the 8 individual Bit Medium 4 To set .

In the third quarter Use HAL Library configuration interrupted

3.1 Correlation function

stay HAL In the library , There are several functions about interrupts .

HAL_NVIC_SetPriorityGrouping： Set interrupt priority grouping , Determine the range of preemption priority and sub priority .

HAL_NVIC_SetPriority： Set the preemptive priority and sub priority of a specific interrupt .

HAL_NVIC_EnableIRQ： Enable a specific interrupt .

HAL_NVIC_DisableIRQ： Close a specific interrupt .

void XXX_IROHandler(void)： A specific interrupt service function .

HAL_XXX_IROHandler(type para):HAL Interrupt service function in Library , stay XXX_IROHandler In the called , What is executed inside is to clear the specific interrupt flag and obtain some states , A callback function for the user will also be called HAL_XXX_Callback.

HAL_XXX_Callback：HAL The callback function called in the interrupt service function in the Library , Users can handle some additional tasks here .

3.2 Usage flow

The above analysis shows that , If you want to use interrupts to achieve your own tasks , Just three steps ：

1、 System interrupt service function relocation ,XXX_IROHandler(void) It is the interrupt function set by the system kernel , This function will be called when an interrupt occurs .

You can see that they all have weak modification ,weak The function is simply when you write a function with the same name as this function , The system will give priority to calling the functions written by yourself ; If you don't rewrite this function , Then the system calls this function by default .

2、 In the relocated system interrupt processing function call HAL The corresponding interrupt handling service function of the Library . So when an interrupt occurs , Actually, the function executed is HAL Functions in the Library .

3、 stay HAL Called in the interrupt service function of the Library Write your own code in the callback function , Achieve the task . You can see HAL The interrupt function in the library will call a callback function after internally clearing the interrupt flag , This callback function is HAL The library is prepared for users . Users write their own code in it , Realize the required functions .

So when an interrupt occurs , The flow of interrupt function is to call back and forth , System function call HAL Library function ,HAL The library function calls the callback function .

Be careful HAL_XXX_Callback： This callback function also uses weak Modified virtual function , So you can write this function directly , You can also find the specific location of this function in the file , Add specific code inside .