delay_s()延时秒= delay_ms()毫秒*1000= delay_us()微秒*1000000

微秒定时器代码

 
void delay_us(uint32_t n)
{

    SysTick->CTRL = 0;         // Disable SysTick，关闭系统定时器

 SysTick->LOAD = SystemCoreClock/1000000*n-1; // 就是nus

 SysTick->LOAD = SystemCoreClock/1000*n-1; // 就是ms

 SysTick->LOAD = SystemCoreClock/1*n-1; // 就是s

    SysTick->VAL  = 0;         // Clear current value as well as count flag，清空当前计数值且清零count flag
    SysTick->CTRL = 5;         // Enable SysTick timer with processor clock，启动系统定时器，其时钟源为处理器时钟168MHz
    while ((SysTick->CTRL & 0x10000)==0);// Wait until count flag is set
    SysTick->CTRL = 0;         // Disable SysTick，关闭系统定时器

}