進(jìn)入OS前的兩步：PendSV(任務(wù)切換)

1 如何設(shè)定PendSV優(yōu)先級(jí)？

NVIC_SYSPRI14 EQU 0xE000ED22
NVIC_PENDSV_PRI EQU 0xFF
    LDR R0, =NVIC_SYSPRI14 LDR R1, =NVIC_PENDSV_PRI
    STRB R1, [R0]

2 如何觸發(fā)PendSV異常？

NVIC_INT_CTRL EQU 0xE000ED04
NVIC_PENDSVSET EQU 0x10000000


LDR R0, =NVIC_INT_CTRL
LDR R1, =NVIC_PENDSVSET
STR R1, [R0]

3 編寫PendSV異常handler

#include "stm32f10x_conf.h"


#define LED0 *((volatile unsigned long *)(0x422101a0)) //PA8


unsigned char flag=0;
void LEDInit(void)
{
    RCC->APB2ENR|=1<<2;
    GPIOA->CRH&=0XFFFFFFF0;
    GPIOA->CRH|=0X00000003;
    GPIOA->ODR|=1<<8;
}


__asm void SetPendSVPro(void)
{
    NVIC_SYSPRI14 EQU 0xE000ED22
    NVIC_PENDSV_PRI EQU 0xFF
    LDR R1, =NVIC_PENDSV_PRI    
    LDR R0, =NVIC_SYSPRI14
    STRB R1, [R0]
    BX LR
}


__asm void TriggerPendSV(void)
{
    NVIC_INT_CTRL EQU 0xE000ED04
    NVIC_PENDSVSET EQU 0x10000000
    LDR R0, =NVIC_INT_CTRL
    LDR R1, =NVIC_PENDSVSET
    STR R1, [R0]
    BX LR
}


int main(void)
{
    SetPendSVPro();
    LEDInit();
    TriggerPendSV();
    while(1);
}


void PendSV_Handler(void)
{
    LED0 = 0;
}

curr_task = 0;

__set_PSP((PSP_array[curr_task] + 16*4));

__set_CONTROL(0x3);

__ISB();

MRS R0, PSP

STMDB R0!,{R4-R11}

LDR R1,=__cpp(&curr_task)
LDR R3,=__cpp(&PSP_array)
LDR R4,=__cpp(&next_task)
LDR R4,[R4]

STR R4,[R1]
Curr_task=next_task
LDR R0,[R3, R4, LSL #2]

LDMIA R0!,{R4-R11}

MSR PSP, R0
PSP=R0。
BX LR

完整代碼：

#include "stm32f10x.h"
#include "stm32f10x_usart.h"
#include "stm32f10x_gpio.h"
#include "stm32f10x_rcc.h"
#include "stdio.h"
#include "misc.h"


#define HW32_REG(ADDRESS)  (*((volatile unsigned long  *)(ADDRESS)))
#define LED0 *((volatile unsigned long *)(0x422101a0)) //PA8
void USART1_Init(void);
void task0(void) ; 
unsigned char flag=1;


uint32_t  curr_task=0;     // 當(dāng)前執(zhí)行任務(wù)
uint32_t  next_task=1;     // 下一個(gè)任務(wù)
uint32_t task0_stack[17];
uint32_t task1_stack[17];
uint32_t  PSP_array[4];


u8 task0_handle=1;
u8 task1_handle=1;


void task0(void) 
{ 
    while(1)
    {
        if(task0_handle==1)
        {
            printf("task0
");
            task0_handle=0;
            task1_handle=1;
        }
    }
}


void task1(void)
{
    while(1)
    {
        if(task1_handle==1)
        {
            printf("task1
");
            task1_handle=0;
            task0_handle=1;
        }
    }
}


void LEDInit(void)
{
    RCC->APB2ENR|=1<<2; 
    GPIOA->CRH&=0XFFFFFFF0;
    GPIOA->CRH|=0X00000003; 
      GPIOA->ODR|=1<<8;
}


__asm void SetPendSVPro(void)
{
NVIC_SYSPRI14   EQU     0xE000ED22
NVIC_PENDSV_PRI EQU           0xFF
    
    LDR     R1, =NVIC_PENDSV_PRI    
    LDR     R0, =NVIC_SYSPRI14    
    STRB    R1, [R0]
    BX      LR
}


__asm void TriggerPendSV(void)
{
NVIC_INT_CTRL   EQU     0xE000ED04                              
NVIC_PENDSVSET  EQU     0x10000000                              


    LDR     R0, =NVIC_INT_CTRL                                 
    LDR     R1, =NVIC_PENDSVSET
    STR     R1, [R0]
    BX      LR
}


int main(void)
{
    USART1_Init();


    SetPendSVPro();
    LEDInit();
    
    printf("OS test
");
    
    PSP_array[0] = ((unsigned int) task0_stack) + (sizeof task0_stack) - 16*4;
    //PSP_array中存儲(chǔ)的為task0_stack數(shù)組的尾地址-16*4，即task0_stack[1023-16]地址
    HW32_REG((PSP_array[0] + (14<<2))) = (unsigned long) task0; /* PC */
    //task0的PC存儲(chǔ)在task0_stack[1023-16]地址  +14<<2中，即task0_stack[1022]中
    HW32_REG((PSP_array[0] + (15<<2))) = 0x01000000;            /* xPSR */
  
    PSP_array[1] = ((unsigned int) task1_stack) + (sizeof task1_stack) - 16*4;
    HW32_REG((PSP_array[1] + (14<<2))) = (unsigned long) task1; /* PC */
    HW32_REG((PSP_array[1] + (15<<2))) = 0x01000000;            /* xPSR */    
    
    /* 任務(wù)0先執(zhí)行 */
    curr_task = 0; 
     
    /* 設(shè)置PSP指向任務(wù)0堆棧的棧頂 */
    __set_PSP((PSP_array[curr_task] + 16*4)); 
    
    SysTick_Config(9000000);
    SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK_Div8);//72/8=9MHZ     
    /* 使用堆棧指針，非特權(quán)級(jí)狀態(tài) */
    __set_CONTROL(0x3);
    
    /* 改變CONTROL后執(zhí)行ISB (architectural recommendation) */
    __ISB();
    
    /* 啟動(dòng)任務(wù)0 */
    task0();  
    //LED0=0;
    while(1);
}


__asm void PendSV_Handler(void)
{ 
    // 保存當(dāng)前任務(wù)的寄存器內(nèi)容
    MRS    R0, PSP     // 得到PSP  R0 = PSP
                       // xPSR, PC, LR, R12, R0-R3已自動(dòng)保存
    STMDB  R0!,{R4-R11}// 保存R4-R11共8個(gè)寄存器得到當(dāng)前任務(wù)堆棧
    
    // 加載下一個(gè)任務(wù)的內(nèi)容
    LDR    R1,=__cpp(&curr_task)
    LDR    R3,=__cpp(&PSP_array)
    LDR    R4,=__cpp(&next_task)
    LDR    R4,[R4]     // 得到下一個(gè)任務(wù)的ID
    STR    R4,[R1]     // 設(shè)置 curr_task = next_task
    LDR    R0,[R3, R4, LSL #2] // 從PSP_array中獲取PSP的值
    LDMIA  R0!,{R4-R11}// 將任務(wù)堆棧中的數(shù)值加載到R4-R11中
  //ADDS   R0, R0, #0x20
    MSR    PSP, R0     // 設(shè)置PSP指向此任務(wù)
 // ORR     LR, LR, #0x04   
    BX     LR          // 返回
                       // xPSR, PC, LR, R12, R0-R3會(huì)自動(dòng)的恢復(fù)
    ALIGN  4
}


void SysTick_Handler(void)
{
    flag=~flag;
    LED0=flag;
    if(curr_task==0)
        next_task=1;
    else
        next_task=0;
    TriggerPendSV();
}


void USART1_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;
    
    /* config USART1 clock */
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 | RCC_APB2Periph_GPIOA, ENABLE);
    
    /* USART1 GPIO config */
    /* Configure USART1 Tx (PA.09) as alternate function push-pull */
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);    
    /* Configure USART1 Rx (PA.10) as input floating */
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOA, &GPIO_InitStructure);
    
    /* USART1 mode config */
    USART_InitStructure.USART_BaudRate = 9600;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    USART_InitStructure.USART_StopBits = USART_StopBits_1;
    USART_InitStructure.USART_Parity = USART_Parity_No ;
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
    USART_Init(USART1, &USART_InitStructure); 
    USART_Cmd(USART1, ENABLE);
}


int fputc(int ch, FILE *f)
{
  USART_SendData(USART1, (unsigned char) ch);
  while (!(USART1->SR & USART_FLAG_TXE));
 
  return (ch);
}