Date: Sun, 7 Oct 2012 20:36:47 +0000 (UTC) From: Warner Losh <imp@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r241333 - head/sys/arm/at91 Message-ID: <201210072036.q97KalP6066720@svn.freebsd.org>
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Author: imp Date: Sun Oct 7 20:36:46 2012 New Revision: 241333 URL: http://svn.freebsd.org/changeset/base/241333 Log: Loop reading the RTC registers until the same values are obtained twice, as advised in the atmel docs. Submitted by: Ian Lapore Modified: head/sys/arm/at91/at91_rtc.c Modified: head/sys/arm/at91/at91_rtc.c ============================================================================== --- head/sys/arm/at91/at91_rtc.c Sun Oct 7 20:17:24 2012 (r241332) +++ head/sys/arm/at91/at91_rtc.c Sun Oct 7 20:36:46 2012 (r241333) @@ -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 ti 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);
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