/**
* @brief Initialize RTT module
*
* The RTT is running at 32768 Hz by default, i.e. @ XOSC32K frequency without
* divider. There are 2 cascaded dividers in the clock path:
*
* - GCLK_GENDIV_DIV(n): between 1 and 31
* - RTC_MODE0_CTRL_PRESCALER_DIVn: between 1 and 1024, see defines in `component_rtc.h`
*
* However the division scheme of GCLK_GENDIV_DIV can be changed by setting
* GCLK_GENCTRL_DIVSEL:
*
* - GCLK_GENCTRL_DIVSEL = 0: Clock divided by GENDIV.DIV (default)
* - GCLK_GENCTRL_DIVSEL = 1: Clock divided by 2^( GENDIV.DIV + 1 )
*/
void rtt_init(void)
{
RtcMode0 *rtcMode0 = &(RTT_DEV);
/* Turn on power manager for RTC */
PM->APBAMASK.reg |= PM_APBAMASK_RTC;
/* RTC uses External 32,768KHz Oscillator because OSC32K isn't accurate
* enough (p1075/1138). Also keep running in standby. */
SYSCTRL->XOSC32K.reg = SYSCTRL_XOSC32K_ONDEMAND |
SYSCTRL_XOSC32K_EN32K |
SYSCTRL_XOSC32K_XTALEN |
SYSCTRL_XOSC32K_STARTUP(6) |
#if RTT_RUNSTDBY
SYSCTRL_XOSC32K_RUNSTDBY |
#endif
SYSCTRL_XOSC32K_ENABLE;
/* Setup clock GCLK2 with divider 1 */
GCLK->GENDIV.reg = GCLK_GENDIV_ID(2) | GCLK_GENDIV_DIV(1);
while (GCLK->STATUS.bit.SYNCBUSY) {}
/* Enable GCLK2 with XOSC32K as source. Use divider without modification
* and keep running in standby. */
GCLK->GENCTRL.reg = GCLK_GENCTRL_ID(2) |
GCLK_GENCTRL_GENEN |
#if RTT_RUNSTDBY
GCLK_GENCTRL_RUNSTDBY |
#endif
GCLK_GENCTRL_SRC_XOSC32K;
while (GCLK->STATUS.bit.SYNCBUSY) {}
/* Connect GCLK2 to RTC */
GCLK->CLKCTRL.reg = GCLK_CLKCTRL_GEN_GCLK2 |
GCLK_CLKCTRL_CLKEN |
GCLK_CLKCTRL_ID(RTC_GCLK_ID);
while (GCLK->STATUS.bit.SYNCBUSY) {}
/* Disable RTC */
rtt_poweroff();
/* Reset RTC */
rtcMode0->CTRL.bit.SWRST = 1;
while (rtcMode0->STATUS.bit.SYNCBUSY || rtcMode0->CTRL.bit.SWRST) {}
/* Configure as 32bit counter with no prescaler and no clear on match compare */
rtcMode0->CTRL.reg = RTC_MODE0_CTRL_MODE_COUNT32 |
RTT_PRESCALER;
while (rtcMode0->STATUS.bit.SYNCBUSY) {}
/* Setup interrupt */
NVIC_EnableIRQ(RTT_IRQ);
/* Enable RTC */
rtt_poweron();
}
void rtc_poweroff(void)
{
rtt_poweroff();
}
