_Context_Switch call

[Ahmet Akkas]

Joel Sherrill wrote:
> 
> Ahmet Akkas wrote:
> >
> > Hi,
> >
> > Could you please tell me why Context Switch routine is called at
> > the beginning of the multitasking? The following is the sequence
> > of the calls until _Context_Switch() is called. Thanks in advance.
> >
> > in  ...(board)/startup/main.c
> >     rtems_initialize_executive_late( bsp_isr_level );
> >
> > in .../exec/sapi/src/exinit.c
> >     _Thread_Start_multitasking();
> >
> > in .../exec/score/src/threadstartmultitasking.c
> >     _Context_Switch( &_Thread_BSP_context, &_Thread_Heir->Registers );
> 
> Exactly. :)
> 
> What you are seeing is that the state of the CPU at initialization
> is saved into "_Thread_BSP_context" so RTEMS can return to the
> BSP's exit code when rtems_shutdown_executive is invoked (see exit()).
> 
> Guessing ahead .. you have executed this far and are getting a
> falt of some sort inside the 1st context switch.  Here are common
> culprits :):
> 
>   + Since this is the first time you are switching TO a task, it
>     is the 1st time a context YOU initialized is being loaded.
>     So you may have initialized the context incorrectly.  You
>     may also have simply restored it incorrectly.

Yes, your guess is right. There are a couple things need to be fixed
in the initialization. Thanks,

>   + You may have enabled interrupts in the restore portion of the
>     switch.  Prior to this call interrupts are off.  This is where
>     interrupts get enabled for the first time.  If the board is
>     generating an unexpected interrupt, then it happens when you
>     enable interrupts (restore processor status/controls register).
> 
> > Ahmet
> 
> --
> Joel Sherrill, Ph.D.             Director of Research & Development
> joel at OARcorp.com                 On-Line Applications Research
> Ask me about RTEMS: a free RTOS  Huntsville AL 35805
>    Support Available             (256) 722-9985

Ahmet