Kinetis Design Studio中的主题 Re: __NOP is not work?

__NOP is not work?

jakewoo — Wed, 09 Mar 2016 01:52:49 GMT

Hi,

Just like pic.

I want to delay 1us,but it is not work.

Re: __NOP is not work?

jakewoo — Wed, 09 Mar 2016 02:29:47 GMT

I found __NOP, it means no use for delay?

Re: __NOP is not work?

ZhangJennie — Thu, 10 Mar 2016 03:05:17 GMT

Hi Jake,

from your code __NOP can be used for delay. can you please test to step over the __NOP, can it work normal?

if you increase the value of delay_cnt, can you see the time cost for delay_us() increased with scope?

Have a great day,
Jennie Zhang

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

Re: __NOP is not work?

jakewoo — Thu, 10 Mar 2016 05:08:16 GMT

Hi，

I try __asm("nop"),and can work.

But __NOP is not work,and jump over the __NOP.It is maybe unbelivable:smileyconfused:.

Re: __NOP is not work?

ZhangJennie — Thu, 10 Mar 2016 10:51:25 GMT

Hi Jake,

__asm("nop") is the right inline assembly syntax.

I would like to suggest you look this article on this related topic.

Extended Inline Assembly with Kinetis Design Studio

can this help you?
Have a great day,
Jennie Zhang

Re: __NOP is not work?

bobpaddock — Wed, 16 Mar 2016 17:57:29 GMT

You did not say what specific ARM part you where using.

NOP is not necessarily a time-consuming depending on the processor. The processor might remove it from the pipeline before it reaches the execution stage. One of the barrier instructions might be more appropriate, for example:

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0552a/CHDEBIEG.html

Also as others noted a NOP must be marked volatile, some compilers such as GCC will remove instructions that have no side-effects. Marking the instruction volatile will make sure that it is not removed by the optimizer.

Re: __NOP is not work?

cbabcock — Mon, 15 Aug 2022 17:38:02 GMT

__NOP is declared as a function, with the prototype void __NOP(void). You need to call it like "__NOP()", not just "__NOP".