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
