position of task variable codes

Eric Norum e.norum at sk.sympatico.ca
Sat Apr 13 17:26:24 UTC 2002

On Friday, April 12, 2002, at 08:38 PM, Joe Black wrote:

> 	Hi, all
> 	Dose the position of rtems_task_variable_add must be in the task?

Yes, the rtems_task_variable_add directive tells RTEMS to add the 
specified variable to the task-switch context of the*calling* task.

> -----------------------------------------------------------------------------------
> 	my case:
> 		in init_task
> 		create task1
> 		call rtems_task_variable_add to add task1's variable
> 		start task1
> 		create task2 (with the same priority of task1)
> 		call rtems_task_variable_add to add task2's variable
> 		start task2

The above code adds the variable to the `init' task twice, so task1 and 
task2 still use the `global' (not per-task) value of the variable.

> 		delete init_task and task1 run
> 		printf task1's variable
> 		suspend task1 and task2 run
> 		printf task2's variable
> 		resume task1
> 		suspend task2 and task1 run
> 		in task1, printf its variable, it failed :(
> 		resume task2 and suspend task1
> 		in task2, printf its variable, failed too
> -----------------------------------------------------------------------------------
> 	I can guarantee the parameters passed to rtems_task_variable_add 
> are OK in the case above.
> 	If I put the rtems_task_variable_add in task1 or task2, it works well
> 	Could anyone tell me how I can resolve the problem? 3x.

It sounds like you have already solved it.  To add a variable to a 
task's context you must call rtems_task_variable_add from that task.  
 From then on any changes made to that variable by that task will be 
local to the task.

Eric Norum <eric.norum at usask.ca>
Department of Electrical Engineering
University of Saskatchewan
Saskatoon, Canada.
Phone: (306) 966-5394   FAX:   (306) 966-5407

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