Re: Hardware Clock

FROM : Gerriet M. Denkmann
DATE : Sat Jul 08 07:38:44 2006

On 08.07.2006, at 00:21, Shawn Erickson wrote:

> On 7/7/06, Gerriet M. Denkmann <<email_removed>> wrote:

>> How can I read the hardware clock?
>> (Not the system clock as in NSDate or gettimeofday, but the thing
>> which keeps the time when the computer is sleeping or turned off).
>>
>> Maybe some Carbon function? Or Unix call? IOKit?

>
> Not sure I understand the question... can you better explain what you
> are trying to do?


(A) Well, to my understanding, there is some hardware hidden in my 
computer which keeps the time when the computer is switched off.

(B) On the other hand, when the computer is running, the CPU keeps 
the time, which then can be accessed via gettimeofday() or NSDate.

This latter time (B) is initialized from (A) at start or at awakening 
from sleep.

The problem: whenever (B) is initialized from (A) a random value in 
the range -0.5 ... +0.5 seconds is added to the time.
To test: make the time (B) equal to the correct wall clock time. 
Sleep. Awake. Compare time to wall clock. See difference of  -0.5 ... 
+0.5 seconds.

What I want to achieve:
1. a better understanding of what is going on.
2. reading the time (A)
3. try to eliminate this random change of time after each awakening.

Gerriet.