#include "delay.h"


static u8  fac_us=0;//us延时倍乘数
static u16 fac_ms=0;//ms延时倍乘数



//初始化延迟函数
//SYSTICK的时钟固定为HCLK时钟的1/8
//SYSCLK:系统时钟

void delay_init(void)	
{
		systick_clksource_set(SYSTICK_CLKSOURCE_HCLK_DIV8);
    fac_us = SystemCoreClock / 8000000;
    fac_ms = (u16)fac_us * 1000;
}


void delay_us(u32 nus)
{
		u32 ctl;
		SysTick->LOAD = (u32)(nus * fac_us);
		SysTick->VAL = 0x0000U;
		do {
        ctl = SysTick->CTRL;
    } while((ctl & SysTick_CTRL_ENABLE_Msk) && !(ctl & SysTick_CTRL_COUNTFLAG_Msk));
		SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
		SysTick->VAL = 0x0000U;
}

//延时nms
//注意nms的范围
//SysTick->LOAD为24位寄存器,所以,最大延时为:
//nms<=0xffffff*8*1000/SYSCLK
//SYSCLK单位为Hz,nms单位为ms
//对72M条件下,nms<=1864 

void delay_ms(u16 nms)
{
		u32 ctl;

    /* reload the count value */
    SysTick->LOAD = (u32)(nms * fac_ms);
    /* clear the current count value */
    SysTick->VAL = 0x0000U;
    /* enable the systick timer */
    SysTick->CTRL = SysTick_CTRL_ENABLE_Msk;
    /* wait for the COUNTFLAG flag set */
    do {
        ctl = SysTick->CTRL;
    } while((ctl & SysTick_CTRL_ENABLE_Msk) && !(ctl & SysTick_CTRL_COUNTFLAG_Msk));
    /* disable the systick timer */
    SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
    /* clear the current count value */
    SysTick->VAL = 0x0000U;
}