RES: Critical Sections, suggested implementation

[Wendell Pereira da Silva]

Hi, Horro.

I) I think the most "standard" way would be using a semaphore with count = 1. That is, a mutex.
II) Maybe it's enough to disable/enable all interrupts at a proper level, since an ISR shall be as short as possible.

Att.
Wendell.

-----Mensagem original-----
De: rtems-users-bounces at rtems.org [mailto:rtems-users-bounces at rtems.org] Em nome de Nicolas Horro
Enviada em: sexta-feira, 3 de abril de 2009 11:06
Para: RTEMS Users
Assunto: Critical Sections, suggested implementation

Hi,

anybody knows if is there a recommended/standard way of defining a
critical section in RTEMS from:

 i) inside a Task context ?
ii) an ISR ?

I'm particulary interested in RTEMS 4.8/ERC32, but i believe this
would be applicable to most architectures.

As far as I know, there are three ways:

------------------------------------------------------------------------------------------

/* --- Alternative 1. Changing Task Mode --- */

rtems_mode g_previous_task_mode;

inline void beginCriticalSection() {
  rtems_task_mode( RTEMS_NO_PREEMPT | RTEMS_INTERRUPT_LEVEL(15),
                   RTEMS_PREEMPT_MASK | RTEMS_INTERRUPT_MASK,
                   g_previous_task_mode);
}

inline void endCriticalSection() {
  rtems_mode tmp;
  rtems_task_mode( *g_previous_task_mode,
                   RTEMS_PREEMPT_MASK | RTEMS_INTERRUPT_MASK,
                   &tmp);
}


/* --- Alternative 2. Changing Interrupt Mask Register --- */

uint32_t g_previous_interrupt_mask_reg;

inline void beginCriticalSection() {
  g_previous_interrupt_mask_reg = *((uint32_t*)INTMSK);
}

inline void endCriticalSection() {
  *((uint32_t*)INTMSK) = g_previous_interrupt_mask_reg;
}


/* --- Alternative 3. Changing Interrupt Level --- */

uint32_t previous_interrupt_level;

inline void beginCriticalSection() {
  previous_interrupt_level = get_interrupt_level();
}

inline void endCriticalSection() {
  set_interrupt_level(previous_interrupt_level);
}

------------------------------------------------------------------------------------------

- Alternative 1 is only for tasks.
- Alternatives 2 and 3 alter hardware registers that might be
important for ISR_Handler (just a thought).

Thanks in advance,

Nicolás Eduardo Horro
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