Reading rtc on FreeBSD

[Peter Jeremy]

Repeating your question will not encourage an answer.

On 2010-Aug-19 13:09:46 +0300, phil hefferan <wdef200 at gmail.com> wrote:
>I've been looking around for how to read the cmos/rtc on FreeBSD. There is
>no hwclock utility in FreeBSD that I can read sources for to see how it is
>done.

The RTC is only accessed within the kernel (/sys/isa/atrtc.c for
i386 and amd64) and read in /sys/kern/subr_rtc.c::inittodr()

>implies that, on FreeBSD, gettimeofday reads the software time and
>settimeofday sets the cmos clock. I read here
>http://www.mail-archive.com/freebsd-hardware@freebsd.org/msg03414.html that
>settimeofday in fact sets both rtc and system time together.

gettimeofday(2) reads the software clock only.
settimeofday(2) writes both the software clock and RTC.

>BUT the source to adjkerntz.c for FreeBSD seems to say that gettimeofday
>reads the CMOS clock not the system time:
>
>/* get local CMOS clock and possible kernel offset */
>if (gettimeofday(&tv, &tz)) {
>    syslog(LOG_ERR, "gettimeofday: %m");
>    return 1;
>}

That comment is incorrect.

>Which is it? Does gettimeofday read the cmos clock/rtc on FreeBSD? If not,
>how do I read the battery-backed clock on FreeBSD?

There is no managed access to the RTC in FreeBSD.  Your only option to
read the RTC is to directly access its IO port registers via io(4) or
i386_set_ioperm(2)

-- 
Peter Jeremy
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