RTC with VBAT - Bare Metal

weblar — Fri, 05 Oct 2012 10:51:55 GMT

I'm trying to get the RTC working on a Kinetis K60 which uses a coin cell for battery backup.

The problem I'm having is that when I reset the system, each time I attempt to read the RTC_TSR using the rtc_get_time function, I always get a TIF (time invalid) flag set in the status register. The only way this can work is if I write RTC_TSR = 0 in the initialization routine, which doesn't seem correct (its meant to be a battery backed-up register, no?).

I'm using the following code...

void rtc_init() {

// Reset the RTC by setting and clearing the SWR bit in the control register

RTC_CR |= RTC_CR_SWR_MASK;

RTC_CR &= ~RTC_CR_SWR_MASK;

RTC_TAR = 0xFFFFFFFF;

// Enable the oscillator

RTC_CR |= RTC_CR_OSCE_MASK;

delay_ms(125);

RTC_TCR = RTC_TCR_CIR(0) | RTC_TCR_TCR(0);

//RTC_TSR = 0;

RTC_TAR = 0;

RTC_TPR = 0;

// Enable the time counter

RTC_SR |= RTC_SR_TCE_MASK;

}

void rtc_set_time(uint32_t ticks) {

// Disable the RTC

RTC_SR &= ~RTC_SR_TCE_MASK;

// Set the new time since UNIX epoch (01/01/1970)

RTC_TSR = ticks;

// Enable the RTC

RTC_SR |= RTC_SR_TCE_MASK;

}

void rtc_get_time(uint32_t *ticks) {

uint32_t sr = RTC_SR;

if (sr & RTC_SR_TIF_MASK) {

// Time Invalid flag set

}

*ticks = RTC_TSR;

}

I'm well aware that I'm probably doing something stupid but I can't for the life of me figure it out.

Any suggestions are very welcome.

Thanks,

Kev

Re: RTC with VBAT - Bare Metal

zhaohuiliu — Tue, 09 Oct 2012 07:20:36 GMT

Hi,

Please read TIF flag and TSR register description more carefully in RM. TSR must be initilized before you can use it. It is a design requirment.

topic Re: RTC with VBAT - Bare Metal in Kinetis Microcontrollers

RTC with VBAT - Bare Metal

Re: RTC with VBAT - Bare Metal