On 09/11/2021 03:46, Chris Johns wrote:
On 20/10/21 2:25 am, Sebastian Huber wrote:
Add new clock manager directives to get all times provided by the
timehands.
Update #4527.
---
For an updated document to review see:
https://ftp.rtems.org/pub/rtems/people/sebh/c-user.pdf
v2: Clarify boot time.
c-user/clock/directives.rst | 835 ++++++++++++++++++++++++++++++++++
c-user/clock/introduction.rst | 81 ++++
2 files changed, 916 insertions(+)
diff --git a/c-user/clock/directives.rst b/c-user/clock/directives.rst
index bdb7680..8f2d7ea 100644
--- a/c-user/clock/directives.rst
+++ b/c-user/clock/directives.rst
@@ -224,6 +224,841 @@ The following constraints apply to this directive:
Applications which are restricted to only use interfaces of the
pre-qualified
feature set of RTEMS shall not use the directive.
+.. Generated from spec:/rtems/clock/if/get-realtime
+
+.. raw:: latex
+
+ \clearpage
+
+.. index:: rtems_clock_get_realtime()
+
+.. _InterfaceRtemsClockGetRealtime:
+
+rtems_clock_get_realtime()
+--------------------------
+
+Gets the time elapsed since the :term:`Unix epoch` measured using
+:term:`CLOCK_REALTIME` in seconds and nanoseconds format.
+
+.. rubric:: CALLING SEQUENCE:
+
+.. code-block:: c
+
+ void rtems_clock_get_realtime( struct timespec *time_snapshot );
+
+.. rubric:: PARAMETERS:
+
+``time_snapshot``
+ This parameter is the pointer to a `struct timespec
+<https://en.cppreference.com/w/c/chrono/timespec>`_ object. The time> +
elapsed since the :term:`Unix epoch` measured using the
+ :term:`CLOCK_REALTIME` at some time point during the directive call will be
+ stored in this object. Calling the directive with a pointer equal to `NULL
+<https://en.cppreference.com/w/c/types/NULL>`_ is undefined behaviour.
Why not return an invalid error status? Same question for the same thing below.
I just documented the existing implementation. If you want an error
status and NULL pointer checks, then we have to add a wrapper function
around the FreeBSD interface. We still have to export the FreeBSD
interface since it is used by libbsd.
The functions just have a single parameter and no return value
currently. Why would someone pass a NULL pointer to such functions?
We could also change
RTEMS_ALIAS(_Timecounter_Nanotime)
void rtems_clock_get_realtime(struct timespec *);
to
rtems_status_code
rtems_clock_get_realtime(struct timespec *time_snapshot)
{
if ( time_snapshot == NULL ) {
return RTEMS_INVALID_ADDRESS;
}
_Timecounter_Nanotime( time_snapshot );
return RTEMS_SUCCESSFUL;
}
However, this is less efficient. You need an extra comparison, a branch,
a stack frame, push/pop of the return address, and an extra function call.
We could also use something like this:
static inline struct timespec rtems_clock_get_realtime(void)
{
struct timespec time_snapshot;
_Timecounter_Nanotime( &time_snapshot );
return time_snapshot;
}
Unfortunately GCC is not able to optimize this.
--
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