AT32F421xx外设驱动2-delay（寄存器）

#include "BspPhy.h"

static uint32_t fac_us;
static uint32_t fac_ms;

void PhyDelayInit()
{
  SysTick->CTRL |= SYSTICK_CLOCK_SOURCE_AHBCLK_NODIV;
  fac_us = system_core_clock / (1000000U);
  fac_ms = fac_us * (1000U);
}

void PhyDelayUs(uint32_t nus)
{
  uint32_t temp = 0;
  SysTick->LOAD = (uint32_t)(nus * fac_us);
  SysTick->VAL = 0x00;
  SysTick->CTRL |= SysTick_CTRL_ENABLE_Msk ;
  do
  {
    temp = SysTick->CTRL;
  }while((temp & 0x01) && !(temp & (1 << 16)));

  SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
  SysTick->VAL = 0x00;
}

void PhyDelayMs(uint16_t nms)
{ 
    uint32_t i;
    for (i = 0; i < nms; i++)
        PhyDelayUs(1000);
}

void PhyDelaySec(uint16_t sec)
{
  uint16_t index;
  for(index = 0; index < sec; index++)
  {
    PhyDelayMs(500);
    PhyDelayMs(500);
  }
}

/******************************delay****************************************/ 
void PhyDelayInit(void);
void PhyDelayUs(uint32_t nus);
void PhyDelayMs(uint16_t nms);
void PhyDelaySec(uint16_t sec);
/*************************************************************************/