Is it safe to nest calls to DisableGlobalIRQ()?

[pcpro178]

I'm working on driver development for the MKL17Z256VLH4.  Is it safe to nest calls to DisableGlobalIRQ()?  How is the primask value used?

[kerryzhou]

Hi Jim,

   You can use the DisableGlobalIRQ, about the primask, it will be returned after your call DisableGlobalIRQ.

You can check the DisableGlobalIRQ function:

static inline uint32_t DisableGlobalIRQ(void)
{
#if defined(CPSR_I_Msk)
    uint32_t cpsr = __get_CPSR() & CPSR_I_Msk;

    __disable_irq();

    return cpsr;
#else
    uint32_t regPrimask = __get_PRIMASK();

    __disable_irq();

    return regPrimask;
#endif
}

About the usage, you can refer to the following code:

 uint32_t irqMaskValue;

irqMaskValue = DisableGlobalIRQ();

    EnableGlobalIRQ(irqMaskValue);

Wish it helps you!

Have a great day,
Kerry

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[pcpro178]

Thanks, Kerry, but my question is about nesting calls to GlobalDisableIRQ(), such as...

void foo(void)

{

    uint32_t primask = GlobalDisableIRQ();

    /* ...do some work... */

    EnableGlobalIRQ(primask);

}

void bar(void)

{

    uint32_t primask = GlobalDisableIRQ();

    /* ...do some work... */

    foo();

    /* ...do some work... */

    EnableGlobalIRQ(primask);

}

Would the above code be valid, such that interrupts would only be re-enabled in function bar, or would interrupts be enabled in function foo, called from function bar?

[kerryzhou · Accepted solution]

Hi Jim,

    About your code, if in the /* ...do some work... */ area, you modify the primask, I think the next

EnableGlobalIRQ(primask);

will be changed, I think this usage may have the risk.

Even if your /* ...do some work... */ didn't modify the primask, I think your code still not very good.

It's better to control the GlobalDisableIRQ and EnableGlobalIRQ in pair, don't have other pair between GlobalDisableIRQ and EnableGlobalIRQ.

I think you can use it like this:

void bar(void)

{

    uint32_t primask = GlobalDisableIRQ();

    /* ...do some work... */

EnableGlobalIRQ(primask);

    foo();

primask = GlobalDisableIRQ();

    /* ...do some work... */

    EnableGlobalIRQ(primask);

}

Have a great day,
Kerry

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