From mboxrd@z Thu Jan  1 00:00:00 1970
To: Jerry Van Baren <vanbaren_gerald@si.com>
Subject: Re: Using realtime clock?
Message-ID: <979132942.3a5c620ec53f9@mail1.serialsystem.com.sg>
Date: Wed, 10 Jan 2001 21:22:22 +0800 (SGT)
From: Jari Nguyen Trung Thanh <jari.nguyen@serialsystem.com.sg>
Cc: linuxppc-embedded@lists.linuxppc.org
References: <3A5BE233.AD8C3560@serialsystem.com.sg> <4.3.2.20010110072315.00bb5230@falcon.si.com>
In-Reply-To: <4.3.2.20010110072315.00bb5230@falcon.si.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Sender: owner-linuxppc-embedded@lists.linuxppc.org
List-Id: <linuxppc-embedded@lists.linuxppc.org>


Thank you, I think that it is the best way which I can do....
May be I'll try to make it simpler.
Thank again,
Jari


Quoting Jerry Van Baren <vanbaren_gerald@si.com>:

>
> 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.
>
> 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.
>
> gvb
>
>
> At 10:30 AM 1/10/01 +0100, Gabriel Paubert wrote:
>
> >On Wed, 10 Jan 2001, Jari Nguyen Trung Thanh wrote:
> >
> > >
> > > Hello,
> > >
> > > I'm a junior, pls help me...
> > > I'm using Hardhat 2.2.14, and I ported it in a custom board
> > > successfully.
> > > This board has its own realtime clock, pls tell me where I can
> > modify in
> > > the kernel
> > > so that all of the time function in linux can use my realtime
> > > clock...such as
> > > date function...or filesystem....
> >
> >You don't want to use the real time clock for this. Getting the time is
> a
> >very frequent opeartion and you don't want to do I/O on every
> >gettimeofday. even if your RTC is (hopefully) in UTC, it  probably does
> >not keep time in the right format for the kernel (it is much more
> likely
> >to use a split format with year, month, day, hour, minutes and seconds
> in
> >different registers). Many do not provide subseconds fields and run off
> a
> >32768kHz watch cystal which provides only 30 microseconds or so
> >resolution.
> >
> >In one word, the RTC is good to save time across reboots and in some
> cases
> >to measure the CPU timebase rate by measuring the number timebase ticks
> >between two second boundaries.
> >
> >
> >         Regards,
> >         Gabriel.
> >
> >
>
>
>


** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/