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Date: Mon, 22 May 2006 13:03:50 +0200
From: Steven Scholz <steven.scholz@imc-berlin.de>
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To: linuxppc-embedded@ozlabs.org
Subject: Re: MPC8xx: resolution of gettimeofday() ?
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Eugene,

>>> Usually on PPC we use timebase to interpolate time between Decrementer 
>>> interrupts. In this case gettimeofday resolution is determined by 
>>> timebase resolution which is quite high (megahertz range).
>> Sorry. I don't understand. What do you mean with "timebase"? Is there a
>> second timer/counter?
> 
> PowerPC has a facility called timebase. This is 64-bit counter which 
> can be accessed using special instructions (mftb, mftbu on 32-bit PPC).
> Counter resolution depends on particular chip implementation, some 
> use core clock, other use bus clock...
> 
> It's similar to the time-stamp counter in Intel CPUs (accessed 
> with rdtsc instruction).
Thanks very much for clearing this!

> Please, refer to PPC arch manuals for more information. Also, if you 
> really interested in how gettimeofday() is implemented, why don't you 
> look at the source code yourself?
I tried. But it's not obvious. Not for me anyway.

-- 
Steven