[PATCH] Let RTEMS provide clock()

Craig Howland howland@LGSInnovations.com
Wed Sep 6 15:25:00 GMT 2017

On 09/06/2017 09:56 AM, Joel Sherrill wrote:
> On 9/6/2017 3:53 AM, Sebastian Huber wrote:
>> On 06/09/17 10:41, Corinna Vinschen wrote:
>>> I just don't quite understand.  Is sysconf(_SC_CLK_TCK) different
>> Yes, the CLOCKS_PER_SEC is a POSIX defined constant and the
>> sysconf(_SC_CLK_TCK) returns the actual system tick frequency. Which is
>> usually 100 or 1000 ticks per second.
> Making it more complicated, the system tick frequency is
> something that the end user can set for each application.
> We just need to make sure that the constant CLOCKS_PER_SECOND
> is appropriate for use with clock() as defined here:
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/clock.html
> Sebastian.. I assume that all that matches up per POSIX, right?
> --joel
CLOCKS_PER_SEC is not necessarily constant on all systems.  It is only POSIX 
which requires it to be fixed (at 1 million).  The C standard defines it as "an 
expression with type clock_t that is the number per second of the value returned 
by the clock function."  (In addition, POSIX does not require microsecond 
accuracy, so the _times_r() return value could simply be scaled to 
CLOCKS_PER_SEC if so desired as an alternative way of doing it.)

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