# Re: rtc again...

- From: Benjamin Herrenschmidt \<hidden\>
- Date: 2000-08-04 15:50:23 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2000/08/9371677
- Thread: https://ratatoskr.run/linuxppc-dev/2000/08/9371675/t.md

```text

>
>	On RS/6000 CHRP (RS/6000 Platform Architecture), RTAS provides
>freeze-time-base and thaw-time-base calls which signal all of the
>processors inan SMP complex to stop and start the TB.  I do not know of
>any functionality within the PowerPC architecture which would allow
>processors to coordinate their TBs without some external intervention.
>
>	Normally AIX boot freezes the TB, zeroes the TB on each processor,
>and then starts the timebase synchronized.  Because the functionality is
>part of RTAS, this can be done at any time.  I do not know what PreP SMP
>systems do and I know that Apple discourages use of RTAS because it is not
>intended to work.

On recent Core99 machines, Apple has a HW timer in the KeyLargo ASIC that
can be used to sync timebases. (It looks like a 64 bits bus-cycle timer,
but I'm not completely sure yet). There's also, I beleive, the OpenPIC timer.

Ben.


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```