Dear List,
I write the rtc module for a PPC driven machine. I wanted to update the
RTC clock when I adjusted the system clock to an external source (ISDN
line). I adjust the time by adjtimex, ADJ_OFFSET_SINGLESHOT. It is working
nicely.
When I tried to switch on the built in possibility to update the hardware
clock ("11 minute mode") I was surpriced. It did not updated it in every
11 minutes only once (sometimes none). I switched on the automatic update
the following way:
txc.modes = 0;
adjtimex(&txc);
txc.modes = ADJ_STATUS;
txc.status &= ~STA_UNSYNC;
adjtimex(&txc);
But this does not really work. :-(
It is mentioned in the man hwclock(8) that I have to turn this feature on:
>>>>>>>>>>>>>>>>> man hwclock(8) >>>>>>>>>>>>>>>>>>>
...
Automatic Hardware Clock Synchronization By the Kernel
You should be aware of another way that the Hardware Clock
is kept synchronized in some systems. The Linux kernel
has a mode wherein it copies the System Time to the Hard
ware Clock every 11 minutes. This is a good mode to use
when you are using something sophisticated like ntp to
keep your System Time synchronized. (ntp is a way to keep
your System Time synchronized either to a time server
somewhere on the network or to a radio clock hooked up to
your system. See RFC 1305).
This mode (we'll call it "11 minute mode") is off until
something turns it on. The ntp daemon xntpd is one thing
that turns it on. You can turn it off by running any
thing, including hwclock --hctosys, that sets the System
Time the old fashioned way.
...
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Unfortunatelly it seems that in the file kernel/timer.c the
second_overflow function swithces off this feature very often.
>>>>>>>>>>>>>> kernel/timer.c >>>>>>>>>>>>>>>>>>>
...
static void second_overflow(void)
{
long ltemp;
/* Bump the maxerror field */
time_maxerror += time_tolerance >> SHIFT_USEC;
if ( time_maxerror > NTP_PHASE_LIMIT ) {
time_maxerror = NTP_PHASE_LIMIT;
time_status |= STA_UNSYNC;
}
...
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
As the time_maxerror is set to NTP_PHASE_LIMIT, it will be true and set
the STA_UNSYNC bit.
How can I keep the "11 minute mode" working??? Setting time_tolerance to 0
is too weird to me.
What should I do???
TIA && Good byte!
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