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comp.protocols.time.ntp
Affichage de l'article :
Linux 11-minute mode (RTC update)
Date :
Le 03 avril 2008
From :
Noob
Sujet :
Linux 11-minute mode (RTC update)
Hello everyone,
I run Linux kernel 2.6.22.1-rt9 and ntpd 4.2.4p0
# adjtimex --print
mode: 0
offset: 77
frequency: -1309904
maxerror: 493576
esterror: 50
status: 1
time_constant: 6
precision: 1
tolerance: 33554432
tick: 10000
raw time: 1207230744s 183249us = 1207230744.183249
In my setup, STA_UNSYNC (0x0040, clock unsynchronized) is 0.
Thus, ntp_synced() returns 1.
Thus the kernel should write the system time to the RTC every
11 minutes; but it does not.
The relevant code is in sync_cmos_clock()
http://lxr.linux.no/linux/kernel/time/ntp.c#L188
I've added several printk() to this function, and it appears
that it is never called.
The relevant timer is defined with the following macro.
static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);
which expands to
static struct timer_list sync_cmos_timer =
{
.function = sync_cmos_clock,
.expires = 0,
.data = 0,
.base = &boot_tvec_bases
};
The problem seems to be that this timer is never armed, to bootstrap
the process. It seems there should be a call to mod_timer() somewhere.
do_adjtimex() calls notify_cmos_timer() unconditionally.
static void notify_cmos_timer(void)
{
if (no_sync_cmos_clock)
mod_timer(&sync_cmos_timer, jiffies + 1);
}
What are the semantics of notify_cmos_timer?
What is it supposed to do?
And what is 'no_sync_cmos_clock' supposed to mean?
/* Disable the cmos update - used by virtualization and embedded */
int no_sync_cmos_clock __read_mostly;
Why would we (re)arm the timer when 'no_sync_cmos_clock' is true?
I'd be grateful for anyone sharing their knowledge.
Regards.
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