TIM_ClearFlag() function in stm32f10x library

[zaalzaalak222]

Posted on July 07, 2012 at 09:02

The content of this function is

/* Clear the flags */   TIMx->SR = (uint16_t)~TIM_FLAG; But I think it must be in this format: /* Clear the flags */   TIMx->SR &= (uint16_t)~TIM_FLAG; a & is needed for correct clear operation on flags, is this correct?

[Tesla DeLorean]

Posted on July 07, 2012 at 12:30

a & is needed for correct clear operation on flags, is this correct?

Wouldn't that introduce hazards by being non-atomic?''This flag is set by hardware only when the corresponding channel is configured in input capture mode. It is cleared by software by writing it to ‘0.'' I can't find a better cite quickly, but the inferred operation is that only a write of a zero bit will stick, and thus the operation is self masking and atomic.

[zaalzaalak222]

Posted on July 13, 2012 at 15:23

In page 394 of RM0008 we  see:

Bit 15:13     Reserved, must be kept at reset value. (for TIMx status register (TIMx_SR) ) but we write 1 to reserved bits! what is the problems of non atomic clear operation?

[Tesla DeLorean]

Posted on July 13, 2012 at 17:08

what is the problems of non atomic clear operation?

That you'd clear an interrupt that asserts in the middle of your non-atomic RMW operation, and you'd never know. Consider for a second what the AND operator does, and now spread that over at least 4-8 cycles.