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Loop reading the RTC registers until the same values are obtained

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twice, as advised in the atmel docs.

Submitted by:	Ian Lapore
This commit is contained in:
imp 2012-10-07 20:36:46 +00:00
parent 182cb719bb
commit cfdf328b7d
1 changed files with 14 additions and 3 deletions
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17
sys/arm/at91/at91_rtc.c
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@ -256,7 +256,7 @@ static int
at91_rtc_gettime(device_t dev, struct timespec *ts)
{
struct clocktime ct;
uint32_t timr, calr;
uint32_t calr, calr2, timr, timr2;
struct at91_rtc_softc *sc;
sc = device_get_softc(dev);
@ -266,8 +266,19 @@ at91_rtc_gettime(device_t dev, struct timespec *ts)
if (RD4(sc, RTC_VER) & (RTC_VER_NVTIM | RTC_VER_NVCAL))
return EINVAL;
timr = RD4(sc, RTC_TIMR);
calr = RD4(sc, RTC_CALR);
/*
* The RTC hardware can update registers while the CPU is reading them.
* The manual advises reading until you obtain the same values twice.
* Interleaving the reads (rather than timr, timr2, calr, calr2 order)
* also ensures we don't miss a midnight rollover/carry between reads.
*/
do {
timr = RD4(sc, RTC_TIMR);
calr = RD4(sc, RTC_CALR);
timr2 = RD4(sc, RTC_TIMR);
calr2 = RD4(sc, RTC_CALR);
} while (timr != timr2 || calr != calr2);
ct.nsec = 0;
ct.sec = RTC_TIMR_SEC(timr);
ct.min = RTC_TIMR_MIN(timr);