单片机如何实现延时1ms或者1us

1us

//适配主频为120MHz的单片机
void Delay_us(int16_t nus) 
{
  int32_t temp; 
  SysTick->LOAD = nus*15; //120MHz
  SysTick->VAL=0X00;
  SysTick->CTRL=0X01;
  do 
  { 
    temp=SysTick->CTRL;
  }
  while((temp&0x01)&&(!(temp&(1<<16))));

  SysTick->CTRL=0x00; 
  SysTick->VAL =0X00; 
}

1ms

void Delay_ms(int16_t t)
{
		unsigned long a;
		a = t;
		while(a--)
		{
				Delay_us(1000);
		}
}