Re: [Xenomai-help] [RTnet-users] Ideas how to measure delays with RTnet

["Karl Reichert" <Karl-Trampe@domain.hid>]

> Gilles Chanteperdrix wrote:
> > Jan Kiszka wrote:
> >  > Karl Reichert wrote:
> >  >  > Jan Kiszka wrote:
> >  >  >> Karl Reichert wrote:
> >  >  >>> Hello,
> >  >  >>>
> >  >  >>> I have two stations running RTnet, one as a master and one as a
> slave. I
> >  >  >> want
> >  >  >>> to measure the time, which a message, sent from master to slave,
> takes.
> >  >  >> But,
> >  >  >>> I don't want the time of the transmission only, but the complete
> time of
> >  >  >> all
> >  >  >>> software layers this data is processed through.
> >  >  >>>
> >  >  >>> _______________     _______________
> >  >  >>> |           A                 |     |               D           
>      |
> >  >  >>> |______________|    |______________|
> >  >  >>> |           B                 |     |               C           
>      |
> >  >  >>> |______________|    |______________|
> >  >  >>> |   RTnet (Master)    |     |    RTnet (Slave)        |
> >  >  >>> |______________|    |______________|
> >  >  >>>             |                                 |
> >  >  >>>             |______________|
> >  >  >>>
> >  >  >>> So, I create the data, that should be send, in Layer A (Master)
> and send
> >  >  >> it
> >  >  >>> over RTnet to Layer D (Slave).
> >  >  >>>
> >  >  >>> I want to take the time when the data leaves A and when it
> arrives D
> >  >  >> with
> >  >  >>> rtdm_clock_read(). If I have the offset between master and
> slave, I can
> >  >  >>> calculate the time it took to pass A, B, both RTnet stacks, C
> and D.
> >  >  >>>
> >  >  >>> As RTnet keeps track of the offset in it's stack, I want to use
> this
> >  >  >> value. Is
> >  >  >>> it possible via the API? I didn't found anything. Or do I have
> to
> >  >  >> manipulate
> >  >  >>> the stack to pass the offset to the higher layers (C and D)?
> >  >  >> If RTmac/TDMA is in use, you can obtain the clock offset via
> >  >  >> RTMAC_RTIOC_TIMEOFFSET from the RTDM device "TDMA<x>" (where
> "<x>"
> >  >  >> corresponds to "rteth<x>").
> >  >  >>
> >  >  >> Jan
> >  >  >>
> >  >  >
> >  >  > When I try to compile my application (xenomai native skin, user
> task), I get an error, saying rtdm_driver.h (which contains the prototype for
> rtdm_clock_read()) is for kernel mode tasks only.
> >  >
> >  >  So you are in userland, obviously...
> >  >
> >  >
> >  >  >
> >  >  > How can I get a timestamp in a xenomai native user task? Is there
> sth equivalent to rtdm_clock_read()? Or do I have to write a kernel task?
> >  >
> >  >  Nope, there is rt_timer_read & Co. for native user-mode
> applications.
> >  >
> >  >  I was about to remark that everything can be found in the API docs -
> but
> >  >  it can't! Any volunteer to add the missing functions from
> native/timer.h
> >  >  to the docs? Maybe there is just something broken for doxygen. TIA!
> >
> >  The problem is that __KERNEL__ is in the list of PREDEFINED macros,
> >  and the comments in native/timer.h are in the !__KERNEL__ section.
> 
> Other headers do #if (defined(__KERNEL__) || defined(__XENO_SIM__)) &&
> !defined(DOXYGEN_CPP)
> Maybe we should use the same construction in native/timer.h ?
> 
> -- 
>  Gilles

Hmm ... what is the difference between rt_timer_read, rt_timer_inquire and rt_timer_tsc? I think rt_timer_inquire is giving the same results (and a little more, the period) like the other two ones, but in one call?

As I understand, TSC is a reliable value on single processor machines with CONFIG_CPU_FREQ, CONFIG_ACPI_PROCESSOR and CONFIG_APM disabled?! So I can use rt_timer_tsc?! Or should I better use rt_timer_read? (Please see above for my UseCase)

Thanks in advance.
Karl
-- 
von Karl Reichert