// 通过直接计算校准RTC时钟(使用0.01ms周期的systick测量再修正RTC预分频系数)。
void RTC_Calibrate(void)
{
unsigned int systick_sta;
unsigned int rtctick_lmt;
unsigned int prescaler = 0;
// 在使用systick测量RTC tick的周期长度之前，初始化systick
NVIC_SetPriority(SysTick_IRQn, 0);
SysTick_Init();
// 开始rtcalarm计数并使能rtcalarm中断
SysTick_Enable();
// 先设置默认的RTC预分频系数(rtc tike = ~1ms)
RTC_SetPrescaler(DEF_RTC_PRESCALER);
/* Enable RTC Clock */
RCC_RTCCLKCmd(ENABLE);
/* Wait for RTC registers synchronization */
RTC_WaitForSynchro();
/* Wait until last write operation on RTC registers has finished */
RTC_WaitForLastTask();
// 测量RTC单周期长度持续~1秒
rtctick_lmt = systick+1000/SYSTICK_PERIOD;
// 记录测量前的systick值
systick_sta = systick;
// 测量1000个周期的rtc tick(~1s)
while(systick < rtctick_lmt);
prescaler = (DEF_RTC_PRESCALER * 1000)/((systick-systick_sta)/100);
// printf("prescaler = %d.\r\n", prescaler);
// 重新设置RTC预分频系数
RTC_SetPrescaler(prescaler);
/* Enable RTC Clock */
RCC_RTCCLKCmd(ENABLE);
/* Wait for RTC registers synchronization */
RTC_WaitForSynchro();
/* Wait until last write operation on RTC registers has finished */
RTC_WaitForLastTask();
// 校准完RTC时钟后，停止rtcalarm计数并禁止rtcalarm中断
SysTick_Disable();
// printf("RTC Clock calibrated.\r\n");
}
/* Sets up system hardware */
static void prvSetupHardware(void)
{
/* LED0 is used for the link status, on = PHY cable detected */
Board_Init();
/* Initial LED state is off to show an unconnected cable state */
Board_LED_Set(0, false);
/* Setup a 1mS sysTick for the primary time base */
SysTick_Enable(1);
}
// ************** SysTick_Init ****************************
// - Initializes the Systick timer
// ********************************************************
// Input: none
// Output: none
// ********************************************************
void SysTick_Init(){
// disable systick while it is being initialized
SysTick_Disable();
// set period to maximum value
SysTick_SetPeriod(0xFFFFFF);
// reset counter value
SysTick_Reset();
// set interrupt priority
SysTick_SetInterruptPriority();
// enable systick
SysTick_Enable();
}