disable interrupts and enable interrupts if they where enabled

RE: disable interrupts and enable interrupts if they where enabled

Susheel Nuguru — Thu, 06 Aug 2015 13:09:54 GMT

It is actually a mask, so i

if ( was_masked )
 __enable_irq();

would mean that "enable it now, even though it was disabled before I disabled it"

RE: disable interrupts and enable interrupts if they where enabled

Torsten Robitzki — Thu, 06 Aug 2015 13:04:05 GMT

And by the way. I was not just using it wrong, but named the variable wrong too. Otherwise "if it was not enabled, enable" makes not sense ;-)

RE: disable interrupts and enable interrupts if they where enabled

Susheel Nuguru — Thu, 06 Aug 2015 12:58:51 GMT

This is actually a good discovery. I will have to point this out to some people :)

RE: disable interrupts and enable interrupts if they where enabled

Torsten Robitzki — Thu, 06 Aug 2015 12:18:59 GMT

Thank you. I was in deed concerned about a race condition. Good point with the special property of the ISR that could possibly introduce the race!

RE: disable interrupts and enable interrupts if they where enabled

Torsten Robitzki — Thu, 06 Aug 2015 12:15:53 GMT

Ups, my code was ment as pseudo code. I wasn't aware that there is a version of __disable_irq() that works like I would expect it. I was looking up the function in core_cm0.h and there it returns void.

RE: disable interrupts and enable interrupts if they where enabled

RK — Thu, 06 Aug 2015 12:04:12 GMT

There's more confusion than that. The __disable_irq() function which returns something is in the ARM toolchain (only I think). The CMSIS function which is in core_cmFunc.h declares it as returning void, and that's the one my compiler picks up at least and I'd think most others would if CMSIS is included.

RE: disable interrupts and enable interrupts if they where enabled

RK — Thu, 06 Aug 2015 12:01:30 GMT

You should be able to use __get_PRIMASK() and __set_PRIMASK() like so

uint32_t old_primask = __get_PRIMASK();
__disable_irq();
manipulation();
__set_PRIMASK( old_primask );

This looks like it might have a race condition but doesn't. If interrupts were enabled and something interrupts you between the __get_PRIMASK() and the __disable_irq() and disables IRQs itself, it will restore them before it finishes so your 'old_primask' variable will still be valid.

RE: disable interrupts and enable interrupts if they where enabled

Susheel Nuguru — Thu, 06 Aug 2015 11:47:45 GMT

I see that ARM documentation says that it returns value of PSR, that is incorrect or it does not make sense, because that is not single bit. It should be PRIMASK

RE: disable interrupts and enable interrupts if they where enabled

Susheel Nuguru — Thu, 06 Aug 2015 11:40:20 GMT

You are using it wrong. The if statement should be

if ( !was_enabled )

infocenter.arm.com/.../index.jsp

The __disable_irq gives you the value of PRIMASK prior to calling that function. If it returns 0, then it means that no interrupts were masked and this current call __disable_irq has set the mask disabling configurable interrupts.

If it returns 1, it means that it was already masked before calling this __disable_irq and enabling interrupts is not done at current context.