[ntp:questions] Linux 11-minute mode (RTC update)

Serge Bets serge.bets at NOSPAM.laposte.invalid
Thu Apr 10 12:50:31 UTC 2008


Hello Maciej,

 On Wednesday, April 9, 2008 at 21:19:55 +0100, Maciej W. Rozycki wrote:

> on some Linux platforms that use the RTC periodic interrupt as the
> source of the system timer interrupt. Updating the RTC causes a
> considerable disruption of the interrupt

I guess this problem is due to the reset of the RTC oscillator, right?
Then a solution could be to use an alternative method to set the RTC,
not using reset, but holding the clock during a fraction of second,
until ticks are in sync. Deliciously hackish, and surely illegal.
Instead of normal:

 -1) wait for the next real half second
 -2) freeze clock
 -3) reset oscillator
 -4) write time
 -5) release clock
 -6) release oscillator

Alternatively do:

 -1) wait for an RTC tick
 -2) freeze clock
 -3) write time + 1 second
 -4) wait for the next real second
 -5) release clock

This holds the clock for up to a second, producing no more update nor
alarm interrupts. But the oscillator still oscillates, so periodic
interrupts should be undisturbed, during and after this procedure.
Interrupts have to be enabled during step #4 of course.

I'm not aware of any tool using this method. What are those PIE-timer
platforms? Do you have one?


Serge.
-- 
Serge point Bets arobase laposte point net




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