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 ()  
    {  
    }  
}  

}

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±ÕËùÓÐÖÐ¶Ï  

}

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

SysClock=(PLL+)\*;  
return SysClock;  

}

二、systick定时器设置

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

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

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

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 * );
}

// 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 * ) + (usTicks * - cycle_cnt) / usTicks;
}

main中使用

cycleCounterInit();  
SysTick\_Config(SystemCoreClock / );