[Click] Fwd: Timestamp and Timers Questions

[Cliff Frey]

I find the easiest way to trace through lots of #if code is to add #error
statements in each branch, and see which ones are hit when compiling.

When running userlevel-linux click, timestamp uses either the clock_gettime
or gettimeofday library functions to get the current time.

Cliff


On Mon, Jul 22, 2013 at 7:57 PM, Bronson Oka <boka at hawaii.edu> wrote:

> Hello,
>
> I was just wondering if you could answer a few questions about the
> implementation of the Click Router.
>
> I'm trying to implement a protocol Element.  The implementation is for
> testing and verification of the protocol, so precision and speed are a
> factor.  I've been looking at the Click source code for the past few weeks
> trying to figure out how precise the Timers and Timestamp are.
>
> Form what I understand, all the Elements that depend on system time rely on
> the Timestamp Element.  The timestamp.hh header file has a definition for
> different inline assign() functions, but there are many #if statements that
> control which macros get defined and I'm not sure how to tell which ones
> are actually being used when compiling the code.
>
> Is there a simple way to tell which #if statements are invoked?
> This would make it much easier to focus on specific parts of the code.
>
> I would also like to ask how the Timestamp gets the system time.  I saw
> that the assign_now() inline function calls current_kernel_time(), but I
> wasn't able to trace this call back to its origin.
>
> When running on Linux, does the Click Router use system calls to get the
> time (such as POSIX)?
>
> I would also greatly appreciate it if you can offer any extra tips for
> understanding the Timestamp implementation.
>
> Thanks for your help.
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