看到示例里面的SYS_Init()中有几行
/* Update System Core Clock */
/* User can use SystemCoreClockUpdate() to calculate PllClock, SystemCoreClock and CycylesPerUs automatically. */
//SystemCoreClockUpdate();
PllClock = PLL_CLOCK; // PLL
SystemCoreClock = PLL_CLOCK / 1; // HCLK
CyclesPerUs = PLL_CLOCK / 1000000; // For SYS_SysTickDelay()
在clk.h
/**
* [url=home.php?mod=space&uid=247401]@brief[/url] This function execute delay function.
* @param[in] us Delay time. The Max value is 2^24 / CPU Clock(MHz). Ex:
* 50MHz => 335544us, 48MHz => 349525us, 28MHz => 699050us ...
* [url=home.php?mod=space&uid=266161]@return[/url] None
* [url=home.php?mod=space&uid=1543424]@Details[/url] Use the SysTick to generate the delay time and the UNIT is in us.
* The SysTick clock source is from HCLK, i.e the same as system core clock.
* User can use SystemCoreClockUpdate() to calculate CyclesPerUs automatically before using this function.
*/
__STATIC_INLINE void CLK_SysTickDelay(uint32_t us)
{
SysTick->LOAD = us * CyclesPerUs;
SysTick->VAL = (0x00);
SysTick->CTRL = SysTick_CTRL_CLKSOURCE_Msk | SysTick_CTRL_ENABLE_Msk;
/* Waiting for down-count to zero */
while((SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk) == 0);
/* Disable SysTick counter */
SysTick->CTRL = 0;
}
| 
楼主
标题置顶
标题高亮
