How to implement a few cycles delay macro or function

[CTabo.1]

Hello,
I need to implement delay macro, lasting just a few cycles.

As the delay is so small I would not like to use TIMs o DWT.

On Texas Instruments DSPs, I was used to implement this nanoseconds delays, using NOP() instructions.
Unfortunately, as also written in STM32 Programming Manual this is not a good pattern on Cortex processors.

On a previous post, related to another issue, I was suggested to use Data Memory Barrier (DMB), Data Synchronization Barrier (DSB), and Instruction Synchronization Barrier (ISB) instructions, instead of NOPs.

How can I use this instructions, to implement a few cycles delay macro?

Regards,
Carlo

[Andrew Neil]

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@CTabo.1 wrote:

it may be necessary to encapsulate the two consecutive readings instructions between #pragma directives to disable any optimizations.

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Possibly, although I'd have thought that the RHS should be qualified as volatile - so might not get optimised?

Maybe alternative to make sts volatile?

[TDK]

> However it may be necessary to encapsulate the two consecutive readings instructions between #pragma directives to disable any optimizations.

Registers are marked as volatile. The compiler must read them on every access in your program.

[CTabo.1]

@TDK , @Andrew Neil 

Yes, you guys are both right.
The registers are markerd as volatile, so eventual optimizations should not create problems.

Thank you very much,
Carlo