Need help in understanding some of the existing code in RTEMS

[Richi Dubey]

>
> During system startup the application configuration defines which
> processor is available to RTEMS. Every configured and present processor
> gets an idle thread assigned which is managed by a scheduler. This is
> the starting point of the system. If someone calls
> rtems_scheduler_remove_processor(), then a processor gets removed from a
> scheduler instance. This processor still has to execute code. For this a
> idle thread is used. This idle thread is not managed by a scheduler. If
> someone uses rtems_scheduler_add_processor() this idle thread is again
> controlled by a scheduler.

This makes sense. Thanks.

On Thu, Jul 16, 2020 at 9:17 PM Sebastian Huber <
sebastian.huber at embedded-brains.de> wrote:

> On 15/07/2020 14:55, Richi Dubey wrote:
>
> > On Wed, Jul 15, 2020 at 5:57 PM Richi Dubey <richidubey at gmail.com
> > <mailto:richidubey at gmail.com>> wrote:
> >
> >     Hi,
> >
> >     I had a small question. The scheduler struct inside percpu.h looks
> >     like:
> >
>  ------------------------------------------------------------------------------------------------------
> >         struct {
> >           /**
> >            * @brief The scheduler control of the scheduler owning this
> >     processor.
> >            *
> >            * This pointer is NULL in case this processor is currently
> >     not used by a
> >            * scheduler instance.
> >            */
> >           const struct _Scheduler_Control *control;
> >
> >           /**
> >            * @brief The scheduler context of the scheduler owning this
> >     processor.
> >            *
> >            * This pointer is NULL in case this processor is currently
> >     not used by a
> >            * scheduler instance.
> >            */
> >           const struct Scheduler_Context *context;
> >
> >           /**
> >            * @brief The idle thread for this processor in case it is
> >     online and
> >            * currently not used by a scheduler instance.
> >            */
> >           struct _Thread_Control *idle_if_online_and_unused;
> >         } Scheduler;
> >
>  ------------------------------------------------------------------------------------------------------
> >     So, does this mean a CPU when active is always either executing an
> >     idle thread and is not being used by a scheduler (so has a thread
> >     attribute in the idle_if_online_and_unused), or is used by a
> >     scheduler and is executing a task ( which can not be an idle
> >     task)? Another equivalent question is do we have an idle scheduler
> >     node, like we have idle predefined threads that run on a CPU?
> >
> During system startup the application configuration defines which
> processor is available to RTEMS. Every configured and present processor
> gets an idle thread assigned which is managed by a scheduler. This is
> the starting point of the system. If someone calls
> rtems_scheduler_remove_processor(), then a processor gets removed from a
> scheduler instance. This processor still has to execute code. For this a
> idle thread is used. This idle thread is not managed by a scheduler. If
> someone uses rtems_scheduler_add_processor() this idle thread is again
> controlled by a scheduler.
>
>
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