accurate gettimeofday_ns() on arm cortex a9 mpcore

[tonyg362 <tonyg3622 at yahoo dot com>]

Hi,

I'm trying to get some accurate timing information on an NVIDIA Tegra2 board
(ARM cortex a9 mpcore, dual core). I see that on ARM architectures the
get_cycles() function simply returns 0, so, in the time.c of systemtap's
runtime code I see that a value of 1000 is simply added to the base time. I
modified this source and made my own __get_cycles() function inside of
time.c. This function reads the value from a periphery global timer. I'm not
sure of the resolution of this timer but, this timer is synchronous with the
global clock (which is max 1GHz) and thus should be a multiple of the actual
cycle counter. This doesn't seem very accurate however. I am not using the
actual cycle counter which is available from the performance monitoring unit
because I am using this for other things, and also it is only a 32 bit
counter and would overflow too often. Is there any other way to get more
accurate timing information on an ARM processor?

thanks,

-Tony
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