[Xenomai-help] What is permanent memory (rt_task_shadow)

[Xenomai-help] What is permanent memory (rt_task_shadow)

[Anders Blomdell]

The documentation for rt_task_shadow says:

   task The address of a task descriptor Xenomai will use to store the
        task-related data. This descriptor must always be valid while
        the task is active therefore it must be allocated in permanent
        memory.

Is it correct to assume that it is OK to the following:

   void func() {
     RT_TASK task;
     int err;

     err = rt_task_shadow(&task, ...);
     ...  Realtime activities ...
     if (err == 0) {
       rt_task_delete(&task);
     }
   }

Regards

Anders Blomdell

-- 
Anders Blomdell                  Email: anders.blomdell@domain.hid
Department of Automatic Control
Lund University                  Phone:    +46 46 222 4625
P.O. Box 118                     Fax:      +46 46 138118
SE-221 00 Lund, Sweden

Re: [Xenomai-help] What is permanent memory (rt_task_shadow)

[Philippe Gerum]

On Fri, 2006-11-24 at 12:46 +0100, Anders Blomdell wrote:
> The documentation for rt_task_shadow says:
> 
>    task The address of a task descriptor Xenomai will use to store the
>         task-related data. This descriptor must always be valid while
>         the task is active therefore it must be allocated in permanent
>         memory.
> 
> Is it correct to assume that it is OK to the following:
> 

Yes, even if it relies on the assumption that func() will never unwind
its stack space before it self-destroys.

>    void func() {
>      RT_TASK task;
>      int err;
> 
>      err = rt_task_shadow(&task, ...);
>      ...  Realtime activities ...
>      if (err == 0) {
>        rt_task_delete(&task);
>      }
>    }
> 
> Regards
> 
> Anders Blomdell
> 
-- 
Philippe.

Re: [Xenomai-help] What is permanent memory (rt_task_shadow)

[Anders Blomdell]

Philippe Gerum wrote:
> On Fri, 2006-11-24 at 12:46 +0100, Anders Blomdell wrote:
>> The documentation for rt_task_shadow says:
>>
>>    task The address of a task descriptor Xenomai will use to store the
>>         task-related data. This descriptor must always be valid while
>>         the task is active therefore it must be allocated in permanent
>>         memory.
>>
>> Is it correct to assume that it is OK to the following:
>>
>>    void func() {
>>      RT_TASK task;
>>      int err;
>>
>>      err = rt_task_shadow(&task, ...);
>>      ...  Realtime activities ...
>>      if (err == 0) {
>>        rt_task_delete(&task);
>>      }
>>    }
> 
> Yes, even if it relies on the assumption that func() will never unwind
> its stack space before it self-destroys.
OK, good. Follow-up question:

   Is there any way to do the inverse of rt_task_shadow (since
   the answer above implies that rt_task_delete will destroy the
   linux task as well)?

Regards

Anders Blomdell

-- 
Anders Blomdell                  Email: anders.blomdell@domain.hid
Department of Automatic Control
Lund University                  Phone:    +46 46 222 4625
P.O. Box 118                     Fax:      +46 46 138118
SE-221 00 Lund, Sweden

Re: [Xenomai-help] What is permanent memory (rt_task_shadow)

[Philippe Gerum]

On Fri, 2006-11-24 at 14:31 +0100, Anders Blomdell wrote:
> Philippe Gerum wrote:
> > On Fri, 2006-11-24 at 12:46 +0100, Anders Blomdell wrote:
> >> The documentation for rt_task_shadow says:
> >>
> >>    task The address of a task descriptor Xenomai will use to store the
> >>         task-related data. This descriptor must always be valid while
> >>         the task is active therefore it must be allocated in permanent
> >>         memory.
> >>
> >> Is it correct to assume that it is OK to the following:
> >>
> >>    void func() {
> >>      RT_TASK task;
> >>      int err;
> >>
> >>      err = rt_task_shadow(&task, ...);
> >>      ...  Realtime activities ...
> >>      if (err == 0) {
> >>        rt_task_delete(&task);
> >>      }
> >>    }
> > 
> > Yes, even if it relies on the assumption that func() will never unwind
> > its stack space before it self-destroys.
> OK, good. Follow-up question:
> 
>    Is there any way to do the inverse of rt_task_shadow (since
>    the answer above implies that rt_task_delete will destroy the
>    linux task as well)?
> 

No interface currently exists for that, even if technically, this could
be done by simply unmapping the shadow (needs a bit more thought for
corner cases, but still, there should be no showstopper). This would be
safe only against the current Linux task though.

> Regards
> 
> Anders Blomdell
> 
-- 
Philippe.