Re: Questions about the Real Time Clock
On Friday, 22 Feb, Donald R. Spoon wrote:
> out. But WHY is it still trying to load something with modprobe? The
> complaints happen right after the hwclock is accessed on boot-up, so I
> suspect it is connected to whatever the hwclock script is doing. I have
Exactly; see below for explanations.
> managed to dream up the following questions for the "gurus":
> 1. Are the "hardware clock" and the "real time clock" the same or are
> they different devices in the BIOS?
They are the same physical device. None of them is "in the BIOS,"
whatever this may mean.
> 2. If they are the same, then does removing RTC support from the kernel
> keep the system from accessing the hardware clock?
Sometimes. There are two methods of accessing the hardware clock: via
/dev/rtc and by directly messing with I/O ports. The first one is
reliable, the second one is not: some Alpha systems exhibit incorrect
behaviour when hardware is accessed directly from user mode code. This is
why hwclock tries /dev/rtc first.
> 3. If different, is RTC support needed in anyway to run the NTPDATE or
> NTP programs?
No. (I know this answer is redundant, because they are not different.)
> 4. If the RTC is not needed and I have support turned off in the
> kernel, can I just remove the /dev/rtc entry and make these complaints
> go away without hurting anyting else on the system?
There are more gentle ways of doing this:
(a) there may be flags to hwclock that prevent it from trying /dev/rtc; or
(b) you can add `alias char-major-10-135 off' to a file in /etc/modutils
(say, /etc/modutils/aliases) and run update-modules.
Removing /dev/rtc should also work (at least for a while).
> that function. The "current" OS is Debian "Woody", and the kernel is
> 2.2.20-generic + 256 Megs of RAM + Matrox Millenium Video card w/ 8 megs.
2.2.x kernels were known for doing silly things in their RTC driver;
don't know if it still holds for the recent ones such as 2.2.20. For
2.2.x, a "light-weight" version of the driver exists as a patch. The
light-weight driver only does what is needed for hwclock, disabling
advanced functionality such as programmable interrupts for user programs.
The RTC driver in 2.4.x is already light-weight.