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

Unruh unruh-spam at physics.ubc.ca
Thu Apr 10 18:14:00 UTC 2008


"Maciej W. Rozycki" <macro at linux-mips.org> writes:

>On Wed, 9 Apr 2008, Unruh wrote:

>> WHAT? What linux platform uses the "1 interrupt per second" of the rtc
>> clock as the timer interrupt? (never mind that the latest motherboards do
>> not have an rtc at all, and use the HPET in poll mode to mimic an rtc).

> A number of DEC platforms have their RTC chip (a Dallas 1287A typically) 
>as the only source of the timer interrupt.  The rate is configurable in 
>powers of two between 2Hz and 8192Hz, with 128Hz and 1024Hz being the 
>commonest with Linux (and elsewhere).  You must be confusing the 
>update-ended interrupt (which is indeed 1Hz) here with the periodic 
>interrupt which may be set to the desired rate.

OK, if you say so. I am used to the CPU timer being very different from the
rtc, but I am only used to PCs. It sounds really weird to have the rtc and
the cpu timer being coupled like that. I would expect the timer to just
keep going, and not to be dependent on the actual value that one stuck into
the rtc.

>  Maciej




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