Re: [avr-libc-dev] [bug #37778] _MemoryBarrier() in cpufunc.h error on compile

[Georg-Johann Lay]

Dmitry Xmelkov a écrit:
> Follow-up Comment #2:
>
> What is the necessity to add memory barrier for _NOP()?
> Common usage, like:
>     PORTB |= 1;
>     _NOP();
>     PORTB &= ~1;
> is safe, as hardware registers are volatile.

Question is whether or not NOP should be allowed to be moved across
ordinary memory moves.

For SEI and CLI, for example, I think this is not wanted in general.

NOP is less intrusive than SEI / CLI, of course, but avr-gcc emits
__builtin_avr_nop() with a memory clobber:

http://gcc.gnu.org/viewcvs/trunk/gcc/config/avr/avr.md?revision=195151&view=markup#l5938