On Tue, 9 Jan 2007, gcworrell wrote:
> Hello.
>
> On our TS-7300's we have found the hw clock drift to be too large to
> support our objectives. To correct this we have replaced the on-board
> hw clocks with another. After replacement, on boot, an error message
> is displayed indicating the hw clock cannot be accessed using any known
> methods. If you manually run the "hwclock" utility with the debug
> option, it says that /dev/rtc cannot be opened because it doesn't
> exist. Upon examination, /dev/rtc does not exist.
Have you written a driver for it? AFAIK the Linux Kernel hasn't yet
been embued with clairvoyance :-)
> What is the mechanism whereby the hw clock is discovered and when
> is /dev/rtc created? Is there something we need to do to get the OS to
> recognize the new clock?
You write a driver for it in the kernel. Check out the TS RTC one as a
prototype.
But I have to ask - do you mean the HW clock drift? I may be teaching my
grandmother to suck eggs, but when the kernel is running, the HW clock
plays no role in timekeeping. The timekeeping is done entirely by the
kernel, by setting appropriate timer interrupts etc and corrections.
On shutdown the system time is written to the HW clock, and on boot the
kenrel reads to current time from the HW clock - the HW clock drift would
affect timing accuracy while the board is powered down.
I know that when the Technologics first ARM board the TS7200 first came
out, the kernel timer interrupt config was very poor, and time keeping was
very poor while running - being many minutes out per day. I fine tuned the
kernel timer interrupt setting and used the adjtimex to fine adjust the
kernel timing to better than 1 sec in 5 days (in my pretty constant temp.
environment).
cheers
Jim
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