interrupt handling on task scheduling

[Joel Sherrill <joel@OARcorp.com>]

Francesco Poletti wrote:
> Hy all,
> We have a porting for the rtems 4.6 working on our simulated arm board.
> We are developing message passing support for a multiprocessor context with the
> help of dedicated hardware.
> We are pointing out some problems in the interrupt handling while the systems is
> supending a task...
> Basically we notice that while we run the command rtems_task_suspend(RTEMS_SELF)
> the OS sometimes performe this sequency of command:
> _CPU_ISR_Disable(level);
> _CPU_ISR_Flash();
> _CPU_ISR_Enable(level)
> 
> _CPU_ISR_Disable(level);
> _CPU_ISR_Enable(level)
> 
> _CPU_ISR_Set_level(); //which enforce the system to reable the interrupt on arm
> processor
> 
> We need that the OS reable the interrupt because we supsend the thread waiting
> for an interrupt and at the same time we have already run
> _CPU_ISR_Disable(level); for give to the critical section of our API the
> interrupt safeness... Of course if none reables the interrupt handling before
> the task suspends then the systems get locked...
> 
> The point is that we were not able to understand from where the
> _CPU_ISR_Set_level()is launched...
> As far as we noticed it's invoked when the new task is scheduled...is it possible?

Interrupt disable levelis part of the per-thread context.  So if a
thread blocks with interrupts disabled, they are potentially reenabled
as part of the switch to another thread.  The IDLE thread should have
interrupts enabled almost all the time (except during switching it
in and out) so if the application threads all disable interrupts, there
will be no interrupt processing until the IDLE thread runs.

I think this matches your described behavior and is expected.  If
a thread disables interrupts and blocks, then they stay disabled
until another thread is switched to.

--joel


> Thanks in advance, Francesco.
> 
> 
> 
> 


-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
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