From mboxrd@z Thu Jan 1 00:00:00 1970 Message-Id: <200101101506.f0AF6j408007@denx.local.net> To: Jerry Van Baren cc: linuxppc-embedded@lists.linuxppc.org Subject: Re: Using realtime clock? From: Wolfgang Denk Mime-version: 1.0 Content-type: text/plain; charset=ISO-8859-1 In-reply-to: Your message of "Wed, 10 Jan 2001 07:33:58 EST." <4.3.2.20010110072315.00bb5230@falcon.si.com> Date: Wed, 10 Jan 2001 16:06:45 +0100 Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: In message <4.3.2.20010110072315.00bb5230@falcon.si.com> Jerry Van Baren wrote: > > The "proper" way to handle a RTC is to read it on power up and set the > system clock based on it. From then on, the system clock will be > correct and everyone will use the system clock efficiently and accurately. Well, that's the way it's often done, but it's far from being perfect. On many embedded systems I'm working with the RTC is running from a high precision oscillator which provides much better accuracy than the system clock. Both clocks will drift, and usually there will be a noticable difference after a few days. This is not really nice. > On the x86 (PC host), the utility is "hwclock" (man hwclock). Your > best approach is to get the source for that, modify it to read your RTC > hardware (which may be different from the PC RTC hardware, although you > might get lucky and only have to deal with endian issues). Then add a > call to it in your startup scripts, typically in /etc/rc.d/rc.local. Any idea how to keep the system clock permanently synchronized to the RTC? Wolfgang Denk -- Software Engineering: Embedded and Realtime Systems, Embedded Linux Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd@denx.de In an infinite universe all things are possible, including the possi- bility that the universe does not exist. - Terry Pratchett, _The Dark Side of the Sun_ ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/