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); } }