STM32时钟设置

一、使用外部时钟，并设置为72MHz

void SetSysClockToHSE(void)
{
    ErrorStatus HSEStartUpStatus;
    /* SYSCLK, HCLK, PCLK2 and PCLK1 configuration -----------------------------*/   
    /* RCC system reset(for debug purpose) */
    RCC_DeInit();

    /* Enable HSE */
    RCC_HSEConfig(RCC_HSE_ON);        //SYSCLK = 8M
    
    /* Disenable LSE */
    RCC_LSEConfig(RCC_LSE_OFF);

    /* Wait till HSE is ready */
    HSEStartUpStatus = RCC_WaitForHSEStartUp();

    if (HSEStartUpStatus == SUCCESS)
    {
        /* HCLK = SYSCLK */
        RCC_HCLKConfig(RCC_SYSCLK_Div1);     //AHB
      
        /* PCLK2 = HCLK */
        RCC_PCLK2Config(RCC_HCLK_Div1);     //High Speed APB

        /* PCLK1 = HCLK */
        RCC_PCLK1Config(RCC_HCLK_Div2);        //Low Speed APB

        /* Flash 0 wait state */
        FLASH_SetLatency(FLASH_Latency_2);
        /*Enable Prefetch Buffer */
        FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);
        
        /* PLLCLK = 8MHz*9 = 72MHz */
        RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9);
        
        /* Select HSE as system clock source */
//        RCC_SYSCLKConfig(RCC_SYSCLKSource_HSE);

        /* Enable PLL */
        RCC_PLLCmd(ENABLE);
        
        /* Wait till PLL is ready */
        while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET) {

        }
        
        /* Select PLL as system clock source */
        RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
        
        /* Wait till PLL is used as system clock source */
        while (RCC_GetSYSCLKSource() != 0x08)
        {
            
        }
    } else {
        /* If HSE fails to start-up, the application will have wrong clock configuration.
        User can add here some code to deal with this error */    

        /* Go to infinite loop */
        while (1)
        {
        }
    }
}

还有之前原子里寄存器版本

char SysClock;

void MYRCC_DeInit(void)
{
    RCC->APB1RSTR = 0x00000000;//¸´Î»½áÊø
    RCC->APB2RSTR = 0x00000000;

    RCC->AHBENR = 0x00000014;  //˯ÃßģʽÉÁ´æºÍSRAMʱÖÓʹÄÜ.ÆäËû¹Ø±Õ.
    RCC->APB2ENR = 0x00000000; //ÍâÉèʱÖӹرÕ.
    RCC->APB1ENR = 0x00000000;
    RCC->CR |= 0x00000001;     //ʹÄÜÄÚ²¿¸ßËÙʱÖÓHSION
    RCC->CFGR &= 0xF8FF0000;   //¸´Î»SW[1:0],HPRE[3:0],PPRE1[2:0],PPRE2[2:0],ADCPRE[1:0],MCO[2:0]
    RCC->CR &= 0xFEF6FFFF;     //¸´Î»HSEON,CSSON,PLLON
    RCC->CR &= 0xFFFBFFFF;     //¸´Î»HSEBYP
    RCC->CFGR &= 0xFF80FFFF;   //¸´Î»PLLSRC, PLLXTPRE, PLLMUL[3:0] and USBPRE
    RCC->CIR = 0x00000000;     //¹Ø±ÕËùÓÐÖжÏ
}

char SystemClock_HSE(u8 PLL)
{
    unsigned char temp=0;
    MYRCC_DeInit();            //¸´Î»²¢ÅäÖÃÏòÁ¿±í
    RCC->CR|=1<<16;       //Íⲿ¸ßËÙʱÖÓʹÄÜHSEON
    while(!(RCC->CR>>17));//µÈ´ýÍⲿʱÖÓ¾ÍÐ÷
    RCC->CFGR=0X00000400; //APB1=DIV2;APB2=DIV1;AHB=DIV1;
    PLL-=2;//µÖÏû2¸öµ¥Î»
    RCC->CFGR|=PLL<<18;   //ÉèÖÃPLLÖµ 2~16
    RCC->CFGR|=1<<16;        //PLLSRC ON
    FLASH->ACR|=0x32;        //FLASH 2¸öÑÓʱÖÜÆÚ
    RCC->CR|=0x01000000;  //PLLON
    while(!(RCC->CR>>25));//µÈ´ýPLLËø¶¨
    RCC->CFGR|=0x00000002;//PLL×÷ΪϵͳʱÖÓ
    while(temp!=0x02)     //µÈ´ýPLL×÷ΪϵͳʱÖÓÉèÖóɹ¦
    {
        temp=RCC->CFGR>>2;
        temp&=0x03;
    }

    SysClock=(PLL+2)*8;
    return SysClock;
}

二、systick定时器设置

/***********SysTick*****************/
// cycles per microsecond
static volatile uint32_t usTicks = 0;
// current uptime for 1kHz systick timer. Will rollover after 49 days. hopefully we won't care.
uint32_t sysTickUptime = 0;

void cycleCounterInit(void)
{
    RCC_ClocksTypeDef clocks;
    RCC_GetClocksFreq(&clocks);
    usTicks = clocks.SYSCLK_Frequency/1000000;
}

// SysTick
void SysTick_Handler(void)
{
    sysTickUptime++;
}
void DelayMs(uint16_t nms)
{
    uint32_t t0=micros();
    while(micros() - t0 < nms * 1000);
}

void delay_us(u32 nus)
{
        uint32_t t0=micros();
        while(micros() - t0 < nus);
}

void delay_ms(uint16_t nms)
{
        uint32_t t0=micros();
        while(micros() - t0 < nms * 1000);
}

// Return system uptime in microseconds (rollover in 70minutes)
// return us
uint32_t micros(void)
{
    register uint32_t ms, cycle_cnt;
    do {
        ms = sysTickUptime;
        cycle_cnt = SysTick->VAL;
    } while (ms != sysTickUptime);
    return (ms * 1000) + (usTicks * 1000 - cycle_cnt) / usTicks;
}

main中使用

    cycleCounterInit();
    SysTick_Config(SystemCoreClock / 1000);